Bruton's tyrosine kinase pleckstrin homology (PH) domain; Btk is a member of the Tec family of cytoplasmic protein tyrosine kinases that includes BMX, IL2-inducible T-cell kinase (Itk) and Tec. Btk plays a role in the maturation of B cells. Tec proteins general have an N-terminal PH domain, followed by a Tek homology (TH) domain, a SH3 domain, a SH2 domain and a kinase domain. The Btk PH domain binds phosphatidylinositol 3,4,5-trisphosphate and responds to signalling via phosphatidylinositol 3-kinase. The PH domain is also involved in membrane anchoring which is confirmed by the discovery of a mutation of a critical arginine residue in the BTK PH domain. This results in severe human immunodeficiency known as X-linked agammaglobulinemia (XLA) in humans and a related disorder is mice.PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652   7 LEEQLIKKSQQKRRTSPSNFKVRFFVLTKASLAYFEDRHGKKRTLKGSIELSRIKCVEIVKSDISipCHYKYPFQVVHDN 86
Cdd:cd01238    1 LEGLLVKRSQGKKRFGPVNYKERWFVLTKSSLSYYEGDGEKRGKEKGSIDLSKVRCVEEVKDEAF--FERKYPFQVVYDD 78

                         90       100       110       120       130       140
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 530354652  87 YLLYVFAPDCESRQRWVLTLKEETRNNNSLVSKYHPNFWMDGRWRCCSQLEKPAVGCAPYDP 148
Cdd:cd01238   79 YTLYVFAPSEEDRDEWIAALRKVCRNNSNLHDKYHPGFWTGGKWSCCGQTSKSAPGCQPAFD 140

Src homology 2 (SH2) domain; In general, SH2 domains are involved in signal transduction; they bind pTyr-containing polypeptide ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites. They are present in a wide array of proteins including: adaptor proteins (Nck1, Crk, Grb2), scaffolds (Slp76, Shc, Dapp1), kinases (Src, Syk, Fps, Tec), phosphatases (Shp-1, Shp-2), transcription factors (STAT1), Ras signaling molecules (Ras-Gap), ubiquitination factors (c-Cbl), cytoskeleton regulators (Tensin), signal regulators (SAP), and phospholipid second messengers (PLCgamma), amongst others.

                         10        20
                 ....*....|....*....|....*...
gi 530354652 232 NNLETYEWYNKSISRDKAEKLLLDTVKK 259
Cdd:cd10396    1 NNLDQYEWYNKNINRSKAEKLLRDEGKE 28

Bruton's tyrosine kinase pleckstrin homology (PH) domain; Btk is a member of the Tec family of cytoplasmic protein tyrosine kinases that includes BMX, IL2-inducible T-cell kinase (Itk) and Tec. Btk plays a role in the maturation of B cells. Tec proteins general have an N-terminal PH domain, followed by a Tek homology (TH) domain, a SH3 domain, a SH2 domain and a kinase domain. The Btk PH domain binds phosphatidylinositol 3,4,5-trisphosphate and responds to signalling via phosphatidylinositol 3-kinase. The PH domain is also involved in membrane anchoring which is confirmed by the discovery of a mutation of a critical arginine residue in the BTK PH domain. This results in severe human immunodeficiency known as X-linked agammaglobulinemia (XLA) in humans and a related disorder is mice.PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652   7 LEEQLIKKSQQKRRTSPSNFKVRFFVLTKASLAYFEDRHGKKRTLKGSIELSRIKCVEIVKSDISipCHYKYPFQVVHDN 86
Cdd:cd01238    1 LEGLLVKRSQGKKRFGPVNYKERWFVLTKSSLSYYEGDGEKRGKEKGSIDLSKVRCVEEVKDEAF--FERKYPFQVVYDD 78

                         90       100       110       120       130       140
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 530354652  87 YLLYVFAPDCESRQRWVLTLKEETRNNNSLVSKYHPNFWMDGRWRCCSQLEKPAVGCAPYDP 148
Cdd:cd01238   79 YTLYVFAPSEEDRDEWIAALRKVCRNNSNLHDKYHPGFWTGGKWSCCGQTSKSAPGCQPAFD 140

Bruton's tyrosine kinase Cys-rich motif; Zinc-binding motif containing conserved cysteines and a histidine. Always found C-terminal to PH domains (but not all PH domains are followed by BTK motifs). The crystal structure shows this motif packs against the PH domain. The PH+Btk module pair has been called the Tec homology (TH) region.

                           10        20        30
                   ....*....|....*....|....*....|....*.
gi 530354652   113 NNSLVSKYHPNFWMDGRWRCCSQLEKPAVGCAPYDP 148
Cdd:smart00107   1 NNNLLQKYHPSFWVDGKWLCCQQSEKNAPGCTPYEA 36

SH3 domain; SH3 (Src homology 3) domains are often indicative of a protein involved in signal transduction related to cytoskeletal organization. First described in the Src cytoplasmic tyrosine kinase. The structure is a partly opened beta barrel.

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|....*..
gi 530354652  177 IALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPS 223
Cdd:pfam00018   1 VALYDYTAQEPDELSFKKGDIIIVLEKSEDGWWKGRNKGGKEGLIPS 47

Src homology 2 (SH2) domain found in Tec protein, IL2-inducible T-cell kinase (Itk); A member of the Tec protein tyrosine kinase Itk is expressed thymus, spleen, lymph node, T lymphocytes, NK and mast cells. It plays a role in T-cell proliferation and differentiation, analogous to Tec family kinases Txk. Itk has been shown to interact with Fyn, Wiskott-Aldrich syndrome protein, KHDRBS1, PLCG1, Lymphocyte cytosolic protein 2, Linker of activated T cells, Karyopherin alpha 2, Grb2, and Peptidylprolyl isomerase A. Most of the Tec family members have a PH domain (Txk and the short (type 1) splice variant of Drosophila Btk29A are exceptions), a Tec homology (TH) domain, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP. It is crucial for the function of Tec PH domains and it's lack of presence in Txk is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homolog also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20
                 ....*....|....*....|....*...
gi 530354652 232 NNLETYEWYNKSISRDKAEKLLLDTVKK 259
Cdd:cd10396    1 NNLDQYEWYNKNINRSKAEKLLRDEGKE 28

Bruton's tyrosine kinase pleckstrin homology (PH) domain; Btk is a member of the Tec family of cytoplasmic protein tyrosine kinases that includes BMX, IL2-inducible T-cell kinase (Itk) and Tec. Btk plays a role in the maturation of B cells. Tec proteins general have an N-terminal PH domain, followed by a Tek homology (TH) domain, a SH3 domain, a SH2 domain and a kinase domain. The Btk PH domain binds phosphatidylinositol 3,4,5-trisphosphate and responds to signalling via phosphatidylinositol 3-kinase. The PH domain is also involved in membrane anchoring which is confirmed by the discovery of a mutation of a critical arginine residue in the BTK PH domain. This results in severe human immunodeficiency known as X-linked agammaglobulinemia (XLA) in humans and a related disorder is mice.PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652   7 LEEQLIKKSQQKRRTSPSNFKVRFFVLTKASLAYFEDRHGKKRTLKGSIELSRIKCVEIVKSDISipCHYKYPFQVVHDN 86
Cdd:cd01238    1 LEGLLVKRSQGKKRFGPVNYKERWFVLTKSSLSYYEGDGEKRGKEKGSIDLSKVRCVEEVKDEAF--FERKYPFQVVYDD 78

                         90       100       110       120       130       140
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 530354652  87 YLLYVFAPDCESRQRWVLTLKEETRNNNSLVSKYHPNFWMDGRWRCCSQLEKPAVGCAPYDP 148
Cdd:cd01238   79 YTLYVFAPSEEDRDEWIAALRKVCRNNSNLHDKYHPGFWTGGKWSCCGQTSKSAPGCQPAFD 140

Src Homology 3 domain of Tec-like Protein Tyrosine Kinases; The Tec (Tyrosine kinase expressed in hepatocellular carcinoma) subfamily is composed of Tec, Btk, Bmx (Etk), Itk (Tsk, Emt), Rlk (Txk), and similar proteins. They are cytoplasmic (or nonreceptor) tyr kinases containing Src homology protein interaction domains (SH3, SH2) N-terminal to the catalytic tyr kinase domain. Most Tec subfamily members (except Rlk) also contain an N-terminal pleckstrin homology (PH) domain, which binds the products of PI3K and allows membrane recruitment and activation. In addition, some members contain the Tec homology (TH) domain, which contains proline-rich and zinc-binding regions. Tec kinases are expressed mainly by haematopoietic cells, although Tec and Bmx are also found in endothelial cells. B-cells express Btk and Tec, while T-cells express Itk, Txk, and Tec. Collectively, Tec kinases are expressed in a variety of myeloid cells such as mast cells, platelets, macrophages, and dendritic cells. Each Tec kinase shows a distinct cell-type pattern of expression. The function of Tec kinases in lymphoid cells have been studied extensively. They play important roles in the development, differentiation, maturation, regulation, survival, and function of B-cells and T-cells. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 530354652 175 LVIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSYLVE 228
Cdd:cd11768    1 IVVALYDFQPIEPGDLPLEKGEEYVVLDDSNEHWWRARDKNGNEGYIPSNYVTE 54

Src Homology 3 domain of Bruton's tyrosine kinase; BTK is a cytoplasmic (or nonreceptor) tyr kinase containing Src homology protein interaction domains (SH3, SH2) N-terminal to the catalytic tyr kinase domain. It also contains an N-terminal pleckstrin homology (PH) domain, which binds the products of PI3K and allows membrane recruitment and activation, and the Tec homology (TH) domain with proline-rich and zinc-binding regions. Btk is expressed in B-cells, and a variety of myeloid cells including mast cells, platelets, neutrophils, and dendrictic cells. It interacts with a variety of partners, from cytosolic proteins to nuclear transcription factors, suggesting a diversity of functions. Stimulation of a diverse array of cell surface receptors, including antigen engagement of the B-cell receptor (BCR), leads to PH-mediated membrane translocation of Btk and subsequent phosphorylation by Src kinase and activation. Btk plays an important role in the life cycle of B-cells including their development, differentiation, proliferation, survival, and apoptosis. Mutations in Btk cause the primary immunodeficiency disease, X-linked agammaglobulinaemia (XLA) in humans. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|...
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSYLVE 228
Cdd:cd11906    3 VVALYDYTPMNAQDLQLRKGEEYVILEESNLPWWRARDKNGREGYIPSNYVTE 55

Src homology 3 domains; Src homology 3 (SH3) domains bind to target proteins through sequences containing proline and hydrophobic amino acids. Pro-containing polypeptides may bind to SH3 domains in 2 different binding orientations.

                           10        20        30        40        50
                   ....*....|....*....|....*....|....*....|....*....|....*
gi 530354652   172 EETLVIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSYL 226
Cdd:smart00326   1 EGPQVRALYDYTAQDPDELSFKKGDIITVLEKSDDGWWKGRLGRGKEGLFPSNYV 55

PH domain; PH stands for pleckstrin homology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652    5 ILLEEQLIKKSQQKRrtspSNFKVRFFVLTKASLAYFEDRHGKK-RTLKGSIELSRIKCVEIVKSDisiPCHYKYPFQVV 83
Cdd:pfam00169   1 VVKEGWLLKKGGGKK----KSWKKRYFVLFDGSLLYYKDDKSGKsKEPKGSISLSGCEVVEVVASD---SPKRKFCFELR 73

                          90       100       110
                  ....*....|....*....|....*....|..
gi 530354652   84 HDNY----LLYVFAPDCESRQRWVLTLKEETR 111
Cdd:pfam00169  74 TGERtgkrTYLLQAESEEERKDWIKAIQSAIR 105

Pleckstrin homology domain; Domain commonly found in eukaryotic signalling proteins. The domain family possesses multiple functions including the abilities to bind inositol phosphates, and various proteins. PH domains have been found to possess inserted domains (such as in PLC gamma, syntrophins) and to be inserted within other domains. Mutations in Brutons tyrosine kinase (Btk) within its PH domain cause X-linked agammaglobulinaemia (XLA) in patients. Point mutations cluster into the positively charged end of the molecule around the predicted binding site for phosphatidylinositol lipids.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652     5 ILLEEQLIKKSQQKRRtspsNFKVRFFVLTKASLAYFEDRHGKKR-TLKGSIELSRIKCVEIVKSDisiPCHYKYPFQVV 83
Cdd:smart00233   1 VIKEGWLYKKSGGGKK----SWKKRYFVLFNSTLLYYKSKKDKKSyKPKGSIDLSGCTVREAPDPD---SSKKPHCFEIK 73

                           90       100
                   ....*....|....*....|....*....
gi 530354652    84 H-DNYLLYVFAPDCESRQRWVLTLKEETR 111
Cdd:smart00233  74 TsDRKTLLLQAESEEEREKWVEALRKAIA 102

First Src Homology 3 domain of Nck adaptor proteins; Nck adaptor proteins regulate actin cytoskeleton dynamics by linking proline-rich effector molecules to protein tyrosine kinases and phosphorylated signaling intermediates. They contain three SH3 domains and a C-terminal SH2 domain. They function downstream of the PDGFbeta receptor and are involved in Rho GTPase signaling and actin dynamics. Vertebrates contain two Nck adaptor proteins: Nck1 (also called Nckalpha) and Nck2 (also called Nckbeta or Growth factor receptor-bound protein 4, Grb4), which show partly overlapping functions but also bind distinct targets. Their SH3 domains are involved in recruiting downstream effector molecules, such as the N-WASP/Arp2/3 complex, which when activated induces actin polymerization that results in the production of pedestals, or protrusions of the plasma membrane. The first SH3 domain of Nck proteins preferentially binds the PxxDY sequence, which is present in the CD3e cytoplasmic tail. This binding inhibits phosphorylation by Src kinases, resulting in the downregulation of TCR surface expression. SH3 domains are protein interaction domains that usually bind to proline-rich ligands with moderate affinity and selectivity, preferentially a PxxP motif. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 530354652 175 LVIALYDYQTNDPQELALRCDEEYYLLDSSEiHWWRVQDKNGHEGYAPSSYL 226
Cdd:cd11765    1 YVVAKYDYTAQGDQELSIKKNEKLTLLDDSK-HWWKVQNSSNQTGYVPSNYV 51

GTPase activating protein 1 m pleckstrin homology (PH) domain; GAP1(m) (also called RASA2/RAS p21 protein activator (GTPase activating protein) 2) is a member of the GAP1 family of GTPase-activating proteins, along with RASAL1, GAP1(IP4BP), and CAPRI. With the notable exception of GAP1(m), they all possess an arginine finger-dependent GAP activity on the Ras-related protein Rap1. GAP1(m) contains two C2 domains, a PH domain, a RasGAP domain, and a BTK domain. Its C2 domains, like those of GAP1IP4BP, do not contain the C2 motif that is known to be required for calcium-dependent phospholipid binding. GAP1(m) is regulated by the binding of its PH domains to phophoinositides, PIP3 (phosphatidylinositol 3,4,5-trisphosphate). It suppresses RAS, enhancing the weak intrinsic GTPase activity of RAS proteins resulting in the inactive GDP-bound form of RAS, allowing control of cellular proliferation and differentiation. GAP1(m) binds inositol tetrakisphosphate (IP4). PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652   4 FILLEEQLIKKSQQKRRTSPSNFKVRFFVLTKASLAYFEDRhGKKRTLkgSIELSRIKCVEivKSDISiPCHYKYPFQVV 83
Cdd:cd13370   15 VHLKEGEMHKRAQGRTRIGKKNFKKRWFCLTSRELTYHKQK-GKEAIF--TIPVKNILAVE--KLEES-AFNKKNMFQVI 88

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|....*
gi 530354652  84 HDNYLLYVFAPDCESRQRWVLTLKEETRNNNSLVSKYHPNFWMDG 128
Cdd:cd13370   89 HSEKPLYVQANNCVEANEWIEVLSRVSRCNQKRLSFYHPSAYLGG 133

Src homology 3 domain of SH3 protein interacting with Nck, 90 kDa (SPIN90); SPIN90 is also called NCK interacting protein with SH3 domain (NCKIPSD), Dia-interacting protein (DIP), 54 kDa vimentin-interacting protein (VIP54), or WASP-interacting SH3-domain protein (WISH). It is an F-actin binding protein that regulates actin polymerization and endocytosis. It associates with the Arp2/3 complex near actin filaments and determines filament localization at the leading edge of lamellipodia. SPIN90 is expressed in the early stages of neuronal differentiation and plays a role in regulating growth cone dynamics and neurite outgrowth. It also interacts with IRSp53 and regulates cell motility by playing a role in the formation of membrane protrusions. SPIN90 contains an N-terminal SH3 domain, a proline-rich domain, and a C-terminal VCA (verprolin-homology and cofilin-like acidic) domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....*....
gi 530354652 178 ALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSYL 226
Cdd:cd11849    4 ALYDFKSAEPNTLSFSEGETFLLLERSNAHWWLVTNHSGETGYVPANYV 52

First Src Homology 3 domain of Nck2 adaptor protein; Nck2 (also called Nckbeta or Growth factor receptor-bound protein 4, Grb4) plays a crucial role in connecting signaling pathways of tyrosine kinase receptors and important effectors in actin dynamics and cytoskeletal remodeling. It binds neuronal signaling proteins such as ephrinB and Disabled-1 (Dab-1) exclusively. Nck adaptor proteins regulate actin cytoskeleton dynamics by linking proline-rich effector molecules to protein tyrosine kinases and phosphorylated signaling intermediates. They contain three SH3 domains and a C-terminal SH2 domain. They function downstream of the PDGFbeta receptor and are involved in Rho GTPase signaling and actin dynamics. Vertebrates contain two Nck adaptor proteins: Nck1 (also called Nckalpha) and Nck2, which show partly overlapping functions but also bind distinct targets. The first SH3 domain of Nck2 binds the PxxDY sequence in the CD3e cytoplasmic tail; this binding inhibits phosphorylation by Src kinases, resulting in the downregulation of TCR surface expression. SH3 domains are protein interaction domains that usually bind to proline-rich ligands with moderate affinity and selectivity, preferentially a PxxP motif. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*...
gi 530354652 172 EETLVIALYDYQTNDPQELALRCDEEYYLLDSSEIhWWRVQDKNGHEGYAPSSYLVEK 229
Cdd:cd11899    2 EEVIVIAKWDYTAQQDQELDIKKNERLWLLDDSKT-WWRVRNAANRTGYVPSNYVERK 58

Src homology 3 domains of the p47phox subunit of NADPH oxidase and similar domains; This family is composed of the tandem SH3 domains of p47phox subunit of NADPH oxidase and Nox Organizing protein 1 (NoxO1), the four SH3 domains of Tks4 (Tyr kinase substrate with four SH3 domains), the five SH3 domains of Tks5, the SH3 domain of obscurin, Myosin-I, and similar domains. Most members of this group also contain Phox homology (PX) domains, except for obscurin and Myosin-I. p47phox and NoxO1 are regulators of the phagocytic NADPH oxidase complex (also called Nox2 or gp91phox) and nonphagocytic NADPH oxidase Nox1, respectively. They play roles in the activation of their respective NADPH oxidase, which catalyzes the transfer of electrons from NADPH to molecular oxygen to form superoxide. Tks proteins are Src substrates and scaffolding proteins that play important roles in the formation of podosomes and invadopodia, the dynamic actin-rich structures that are related to cell migration and cancer cell invasion. Obscurin is a giant muscle protein that plays important roles in the organization and assembly of the myofibril and the sarcoplasmic reticulum. Type I myosins (Myosin-I) are actin-dependent motors in endocytic actin structures and actin patches. They play roles in membrane traffic in endocytic and secretory pathways, cell motility, and mechanosensing. Myosin-I contains an N-terminal actin-activated ATPase, a phospholipid-binding TH1 (tail homology 1) domain, and a C-terminal extension which includes an F-actin-binding TH2 domain, an SH3 domain, and an acidic peptide that participates in activating the Arp2/3complex. The SH3 domain of myosin-I is required for myosin-I-induced actin polymerization. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|
gi 530354652 177 IALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQdKNGHEGYAPSSYL 226
Cdd:cd11856    3 VAIADYEAQGDDEISLQEGEVVEVLEKNDSGWWYVR-KGDKEGWVPASYL 51

Variant SH3 domain;

                          10        20        30        40
                  ....*....|....*....|....*....|....*....|....*....
gi 530354652  178 ALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDkNGHEGYAPSSYL 226
Cdd:pfam14604   1 ALYPYEPKDDDELSLQRGDVITVIEESEDGWWEGIN-TGRTGLVPANYV 48

First Src Homology 3 domain of Nck1 adaptor protein; Nck1 (also called Nckalpha) plays a crucial role in connecting signaling pathways of tyrosine kinase receptors and important effectors in actin dynamics and cytoskeletal remodeling. It binds and activates RasGAP, resulting in the downregulation of Ras. It is also involved in the signaling of endothilin-mediated inhibition of cell migration. Nck adaptor proteins regulate actin cytoskeleton dynamics by linking proline-rich effector molecules to protein tyrosine kinases and phosphorylated signaling intermediates. They contain three SH3 domains and a C-terminal SH2 domain. They function downstream of the PDGFbeta receptor and are involved in Rho GTPase signaling and actin dynamics. Vertebrates contain two Nck adaptor proteins: Nck1 (also called Nckalpha) and Nck2, which show partly overlapping functions but also bind distinct targets. The first SH3 domain of Nck1 binds the PxxDY sequence in the CD3e cytoplasmic tail; this binding inhibits phosphorylation by Src kinases, resulting in the downregulation of TCR surface expression. SH3 domains are protein interaction domains that usually bind to proline-rich ligands with moderate affinity and selectivity, preferentially a PxxP motif. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*....
gi 530354652 172 EETLVIALYDYQTNDPQELALRCDEEYYLLDSSEiHWWRVQDKNGHEGYAPSSYLVEKS 230
Cdd:cd11900    1 EEVVVVAKFDYVAQQDQELDIKKNERLWLLDDSK-SWWRVRNAMNKTGFVPSNYVERKN 58

Src homology 2 (SH2) domain found in Tec protein, IL2-inducible T-cell kinase (Itk); A member of the Tec protein tyrosine kinase Itk is expressed thymus, spleen, lymph node, T lymphocytes, NK and mast cells. It plays a role in T-cell proliferation and differentiation, analogous to Tec family kinases Txk. Itk has been shown to interact with Fyn, Wiskott-Aldrich syndrome protein, KHDRBS1, PLCG1, Lymphocyte cytosolic protein 2, Linker of activated T cells, Karyopherin alpha 2, Grb2, and Peptidylprolyl isomerase A. Most of the Tec family members have a PH domain (Txk and the short (type 1) splice variant of Drosophila Btk29A are exceptions), a Tec homology (TH) domain, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP. It is crucial for the function of Tec PH domains and it's lack of presence in Txk is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homolog also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20
                 ....*....|....*....|....*...
gi 530354652 232 NNLETYEWYNKSISRDKAEKLLLDTVKK 259
Cdd:cd10396    1 NNLDQYEWYNKNINRSKAEKLLRDEGKE 28

Src homology 3 domain of Yes Protein Tyrosine Kinase; Yes (or c-Yes) is a member of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. c-Yes kinase is the cellular homolog of the oncogenic protein (v-Yes) encoded by the Yamaguchi 73 and Esh sarcoma viruses. It displays functional overlap with other Src subfamily members, particularly Src. It also shows some unique functions such as binding to occludins, transmembrane proteins that regulate extracellular interactions in tight junctions. Yes also associates with a number of proteins in different cell types that Src does not interact with, like JAK2 and gp130 in pre-adipocytes, and Pyk2 in treated pulmonary vein endothelial cells. Although the biological function of Yes remains unclear, it appears to have a role in regulating cell-cell interactions and vesicle trafficking in polarized cells. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 530354652 174 TLVIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKN-GHEGYAPSSYLV 227
Cdd:cd12007    1 TIFVALYDYEARTTEDLSFKKGERFQIINNTEGDWWEARSIAtGKNGYIPSNYVA 55

N-terminal Src Homology 3 domain of Ct10 Regulator of Kinase adaptor proteins; CRK adaptor proteins consists of SH2 and SH3 domains, which bind tyrosine-phosphorylated peptides and proline-rich motifs, respectively. They function downstream of protein tyrosine kinases in many signaling pathways started by various extracellular signals, including growth and differentiation factors. Cellular CRK (c-CRK) contains a single SH2 domain, followed by N-terminal and C-terminal SH3 domains. It is involved in the regulation of many cellular processes including cell growth, motility, adhesion, and apoptosis. CRK has been implicated in the malignancy of various human cancers. The N-terminal SH3 domain of CRK binds a number of target proteins including DOCK180, C3G, SOS, and cABL. The CRK family includes two alternatively spliced protein forms, CRKI and CRKII, that are expressed by the CRK gene, and the CRK-like (CRKL) protein, which is expressed by a distinct gene (CRKL). SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSYlVEK 229
Cdd:cd11758    3 VRALFDFPGNDDEDLPFKKGEILTVIRKPEEQWWNARNSEGKTGMIPVPY-VEK 55

Src homology 3 domain of Apoptosis Stimulating of p53 proteins (ASPP); The ASPP family of proteins bind to important regulators of apoptosis (p53, Bcl-2, and RelA) and cell growth (APCL, PP1). They share similarity at their C-termini, where they harbor a proline-rich region, four ankyrin (ANK) repeats, and an SH3 domain. Vertebrates contain three members of the family: ASPP1, ASPP2, and iASPP. ASPP1 and ASPP2 activate the apoptotic function of the p53 family of tumor suppressors (p53, p63, and p73), while iASPP is an oncoprotein that specifically inhibits p53-induced apoptosis. The expression of ASPP proteins is altered in tumors; ASPP1 and ASPP2 are downregulated whereas iASPP is upregulated is some cancer types. ASPP proteins also bind and regulate protein phosphatase 1 (PP1), and this binding is competitive with p53 binding. The SH3 domain and the ANK repeats of ASPP contribute to the p53 binding site; they bind to the DNA binding domain of p53. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*.
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLL---DSSEIHWW--RVQDKnghEGYAPSSYL 226
Cdd:cd11807    3 VYALFDYEAENGDELSFREGDELTVLrkgDDDETEWWwaRLNDK---EGYVPRNLL 55

Src homology 3 domain of Type I fungal Myosins; Type I myosins (myosin-I) are actin-dependent motors in endocytic actin structures and actin patches. They play roles in membrane traffic in endocytic and secretory pathways, cell motility, and mechanosensing. Saccharomyces cerevisiae has two myosins-I, Myo3 and Myo5, which are involved in endocytosis and the polarization of the actin cytoskeleton. Myosin-I contains an N-terminal actin-activated ATPase, a phospholipid-binding TH1 (tail homology 1) domain, and a C-terminal extension which includes an F-actin-binding TH2 domain, an SH3 domain, and an acidic peptide that participates in activating the Arp2/3complex. The SH3 domain of myosin-I is required for myosin-I-induced actin polymerization. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 530354652 178 ALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGH-EGYAPSSYLVE 228
Cdd:cd11858    4 ALYDFAGSVANELSLKKDDIVYIVQKEDNGWWLAKKLDESkEGWVPAAYLEE 55

SH3 domain; This entry represents an SH3 domain.

                          10        20        30        40        50        60
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....
gi 530354652  156 PLPPtpednRRS-FQEPeeTLVIALYDYQTNdpqELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPS 223
Cdd:pfam17902   1 PLKQ-----RRSpVTRP--IPVKALCDYKQG---EVTVEKGEECTLLDNSDREKWKVQTSSGVEKLVPS 59

Src homology 3 domain of ARHGEF9-like Rho guanine nucleotide exchange factors; Members of this family contain a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains. They include the Rho guanine nucleotide exchange factors ARHGEF9, ASEF (also called ARHGEF4), ASEF2, and similar proteins. GEFs activate small GTPases by exchanging bound GDP for free GTP. ARHGEF9 specifically activates Cdc42, while both ASEF and ASEF2 can activate Rac1 and Cdc42. ARHGEF9 is highly expressed in the brain and it interacts with gephyrin, a postsynaptic protein associated with GABA and glycine receptors. ASEF plays a role in angiogenesis and cell migration. ASEF2 is important in cell migration and adhesion dynamics. ASEF exists in an autoinhibited form and is activated upon binding of the tumor suppressor APC (adenomatous polyposis coli), leading to the activation of Rac1 or Cdc42. In its autoinhibited form, the SH3 domain of ASEF forms an extensive interface with the DH and PH domains, blocking the Rac binding site. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....
gi 530354652 175 LVIALYDYQTNDPQELALRCDEEYYLLDSSEIHWW--RVQDKnghEGYAPSSYL 226
Cdd:cd11828    1 LAEALWDHVTMDPEELGFKAGDVIEVLDMSDKDWWwgSIRDE---EGWFPASFV 51

Third Src Homology 3 domain of the fungal endocytic adaptor protein Sla1p; Sla1p facilitates endocytosis by playing a role as an adaptor protein in coupling components of the actin cytoskeleton to the endocytic machinery. It interacts with Abp1p, Las17p and Pan1p, which are activator proteins of actin-related protein 2/3 (Arp2/3). Sla1p contains multiple domains including three SH3 domains, a SAM (sterile alpha motif) domain, and a Sla1 homology domain 1 (SHD1), which binds to the NPFXD motif that is found in many integral membrane proteins such as the Golgi-localized Arf-binding protein Lsb5p and the P4-ATPases, Drs2p and Dnf1p. The third SH3 domain of Sla1p can bind ubiquitin while retaining the ability to bind proline-rich ligands; monoubiquitination of target proteins signals internalization and sorting through the endocytic pathway. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 530354652 177 IALYDYQTNDPQELALRCDEEYYLLDSSEIH-WWRVQD-KNGHEGYAPSSYL 226
Cdd:cd11775    4 KVLYDFDAQSDDELTVKEGDVVYILDDKKSKdWWMVENvSTGKEGVVPASYI 55

Src Homology 3 domain of fungal peroxisomal membrane protein Pex13p; Pex13p, located in the peroxisomal membrane, contains two transmembrane regions and a C-terminal SH3 domain. It binds to the peroxisomal targeting type I (PTS1) receptor Pex5p and the docking factor Pex14p through its SH3 domain. It is essential for both PTS1 and PTS2 protein import pathways into the peroxisomal matrix. Pex13p binds Pex14p, which contains a PxxP motif, in a classical fashion to the proline-rich ligand binding site of its SH3 domain. It binds the WxxxF/Y motif of Pex5p in a novel site that does not compete with Pex14p binding. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 530354652 178 ALYDYQTNDPQ-ELALRCDEEYYLLDSSEI-----HWWRVQDKNGHEGYAPSSYL 226
Cdd:cd11771    4 ALYDFTPENPEmELSLKKGDIVAVLSKTDPlgrdsEWWKGRTRDGRIGWFPSNYV 58

Src Homology 3 domain of Sorting Nexin 9 and similar proteins; Sorting nexins (SNXs) are Phox homology (PX) domain containing proteins that are involved in regulating membrane traffic and protein sorting in the endosomal system. SNXs differ from each other in their lipid-binding specificity, subcellular localization and specific function in the endocytic pathway. This subfamily consists of SH3 domain containing SNXs including SNX9, SNX18, SNX33, and similar proteins. SNX9 is localized to plasma membrane endocytic sites and acts primarily in clathrin-mediated endocytosis, while SNX18 is localized to peripheral endosomal structures, and acts in a trafficking pathway that is clathrin-independent but relies on AP-1 and PACS1. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|..
gi 530354652 178 ALYDYQTNDPQELALRCDEEYYLLDSSEIH-WWRVQDKNGHEGYAPSSYlVE 228
Cdd:cd11763    4 ALYDFDSQPSGELSLRAGEVLTITRQDVGDgWLEGRNSRGEVGLFPSSY-VE 54

GAP1(IP4BP) pleckstrin homology (PH) domain; GAP1 (also called IP4BP, RASA3/Ras GTPase-activating protein 3, and RAS p21 protein activator (GTPase activating protein) 3/GAPIII/MGC46517/MGC47588)) is a member of the GAP1 family of GTPase-activating proteins, along with RASAL1, GAP1(m), and CAPRI. With the notable exception of GAP1(m), they all possess an arginine finger-dependent GAP activity on the Ras-related protein Rap1. GAP1(IP4BP) contains two C2 domains, a PH domain, a RasGAP domain, and a BTK domain. Its C2 domains, like those of GAP1M, do not contain the C2 motif that is known to be required for calcium-dependent phospholipid binding. GAP1(IP4BP) is regulated by the binding of its PH domains to phophoinositides, PIP3 (phosphatidylinositol 3,4,5-trisphosphate) and PIP2 (phosphatidylinositol 4,5-bisphosphate). It suppresses RAS, enhancing the weak intrinsic GTPase activity of RAS proteins resulting in the inactive GDP-bound form of RAS, allowing control of cellular proliferation and differentiation. GAP1(IP4BP) binds tyrosine-protein kinase, HCK. Members here include humans, chickens, frogs, and fish. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 530354652   5 ILLEEQ-LIKKSQQKRRTSPSNFKVRFFVLTKASLAYFEDRHGKKRTlkgSIELSRIKCVEIVKSDisiPCHYKYPFQVV 83
Cdd:cd13371   15 ILLKEGfMIKRAQGRKRFGMKNFKKRWFRLTNHEFTYHKSKGDHPLC---SIPIENILAVERLEEE---SFKMKNMFQVI 88

                         90       100       110
                 ....*....|....*....|....*....|....*..
gi 530354652  84 HDNYLLYVFAPDCESRQRWVLTLKEETRNNNSLVSKY 120
Cdd:cd13371   89 QPERALYIQANNCVEAKDWIDILTKVSQCNKKRLTVY 125

Fifth Src homology 3 domain (or SH3E) of Intersectin-2; Intersectin-2 (ITSN2) is an adaptor protein that functions in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction. It plays a role in clathrin-coated pit (CCP) formation. It binds to many proteins through its multidomain structure and facilitate the assembly of multimeric complexes. ITSN2 also functions as a specific GEF for Cdc42 activation in epithelial morphogenesis, and is required in mitotic spindle orientation. It exists in alternatively spliced short and long isoforms. The short isoform contains two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoform, in addition, contains RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. The fifth SH3 domain (or SH3E) of ITSN2 is expected to bind protein partners, similar to ITSN1 which has been shown to bind many protein partners including SGIP1, Sos1, dynamin1/2, CIN85, c-Cbl, SHIP2, N-WASP, and synaptojanin-1, among others. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRvQDKNGHEGYAPSSYL 226
Cdd:cd11996    3 VIAMYDYTANNEDELSFSKGQLINVLNKDDPDWWQ-GEINGVTGLFPSNYV 52

Fifth Src homology 3 domain (or SH3E) of Intersectin; Intersectins (ITSNs) are adaptor proteins that function in exo- and endocytosis, actin cytoskeletal reorganization, and signal transduction. They are essential for initiating clathrin-coated pit formation. They bind to many proteins through their multidomain structure and facilitate the assembly of multimeric complexes. Vertebrates contain two ITSN proteins, ITSN1 and ITSN2, which exist in alternatively spliced short and long isoforms. The short isoforms contain two Eps15 homology domains (EH1 and EH2), a coiled-coil region and five SH3 domains (SH3A-E), while the long isoforms, in addition, contain RhoGEF (also called Dbl-homologous or DH), Pleckstrin homology (PH) and C2 domains. ITSN1 and ITSN2 are both widely expressed, with variations depending on tissue type and stage of development. The fifth SH3 domain (or SH3E) of ITSN1 has been shown to bind many protein partners including SGIP1, Sos1, dynamin1/2, CIN85, c-Cbl, SHIP2, N-WASP, and synaptojanin-1, among others. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRvQDKNGHEGYAPSSY 225
Cdd:cd11840    2 VIALFPYTAQNEDELSFQKGDIINVLSKDDPDWWR-GELNGQTGLFPSNY 50

Src homology 2 (SH2) domain found in Tec protein, Txk; A member of the Tec protein tyrosine kinase Txk is expressed in thymus, spleen, lymph node, T lymphocytes, NK cells, mast cell lines, and myeloid cell line. Txk plays a role in TCR signal transduction, T cell development, and selection which is analogous to the function of Itk. Txk has been shown to interact with IFN-gamma. Unlike most of the Tec family members Txk lacks a PH domain. Instead Txk has a unique region containing a palmitoylated cysteine string which has a similar membrane tethering function as the PH domain. Txk also has a zinc-binding motif, a SH3 domain, a SH2 domain, and a protein kinase catalytic domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP and crucial to the function of the PH domain. It is not present in Txk which is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homolog also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state. In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.

                         10        20
                 ....*....|....*....|.
gi 530354652 233 NLETYEWYNKSISRDKAEKLL 253
Cdd:cd10398    2 NLEIYEWYHKNITRNQAERLL 22

Src homology 3 domain of Cortactin and related proteins; This subfamily includes cortactin, Abp1 (actin-binding protein 1), hematopoietic lineage cell-specific protein 1 (HS1), and similar proteins. These proteins are involved in regulating actin dynamics through direct or indirect interaction with the Arp2/3 complex, which is required to initiate actin polymerization. They all contain at least one C-terminal SH3 domain. Cortactin and HS1 bind Arp2/3 and actin through an N-terminal region that contains an acidic domain and several copies of a repeat domain found in cortactin and HS1. Abp1 binds actin via an N-terminal actin-depolymerizing factor (ADF) homology domain. Yeast Abp1 binds Arp2/3 directly through two acidic domains. Mammalian Abp1 does not directly interact with Arp2/3; instead, it regulates actin dynamics indirectly by interacting with dynamin and WASP family proteins. The C-terminal region of these proteins acts as an adaptor or scaffold that can connect membrane trafficking and signaling proteins that bind the SH3 domain within the actin network. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....*....
gi 530354652 177 IALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGHEGYAPSSY 225
Cdd:cd11819    3 KALYDYQAAEDNEISFVEGDIITQIEQIDEGWWLGVNAKGQKGLFPANY 51

Src homology 3 domain of Signal Transducing Adaptor Molecule 1; STAM1 is part of the endosomal sorting complex required for transport (ESCRT-0) and is involved in sorting ubiquitinated cargo proteins from the endosome. It may also be involved in the regulation of IL2 and GM-CSF mediated signaling, and has been implicated in neural cell survival. STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGhEGYAPSSYL 226
Cdd:cd11964    3 VRAIYDFEAAEDNELTFKAGDIITILDDSDPNWWKGETPQG-TGLFPSNFV 52

Src homology 3 domain of Signal Transducing Adaptor Molecules; STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. There are two vertebrate STAMs, STAM1 and STAM2, which may be functionally redundant; vertebrate STAMs contain ITAM motifs. They are part of the endosomal sorting complex required for transport (ESCRT-0). STAM2 deficiency in mice did not cause any obvious abnormality, while STAM1 deficiency resulted in growth retardation. Loss of both STAM1 and STAM2 in mice proved lethal, indicating that STAMs are important for embryonic development. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQDKNGhEGYAPSSY 225
Cdd:cd11820    3 VRALYDFEAAEDNELTFKAGEIITVLDDSDPNWWKGSNHRG-EGLFPANF 51

Src homology 3 domain of Protein arginine N-methyltransferase 2; PRMT2, also called HRMT1L1, belongs to the arginine methyltransferase protein family. It functions as a coactivator to both estrogen receptor alpha (ER-alpha) and androgen receptor (AR), presumably through arginine methylation. The ER-alpha transcription factor is involved in cell proliferation, differentiation, morphogenesis, and apoptosis, and is also implicated in the development and progression of breast cancer. PRMT2 and its variants are upregulated in breast cancer cells and may be involved in modulating the ER-alpha signaling pathway during formation of breast cancer. PRMT2 also plays a role in regulating the function of E2F transcription factors, which are critical cell cycle regulators, by binding to the retinoblastoma gene product (RB). It contains an N-terminal SH3 domain and an AdoMet binding domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQdKNGHEGYAPSSYL 226
Cdd:cd11806    2 YVAIADFVATDDSQLSFESGDKLLVLRKPSVDWWWAE-HNGCCGYIPASHL 51

Src homology 3 domain of Src Protein Tyrosine Kinase; Src (or c-Src) is a cytoplasmic (or non-receptor) PTK and is the vertebrate homolog of the oncogenic protein (v-Src) from Rous sarcoma virus. Together with other Src subfamily proteins, it is involved in signaling pathways that regulate cytokine and growth factor responses, cytoskeleton dynamics, cell proliferation, survival, and differentiation. Src also play a role in regulating cell adhesion, invasion, and motility in cancer cells, and tumor vasculature, contributing to cancer progression and metastasis. Elevated levels of Src kinase activity have been reported in a variety of human cancers. Several inhibitors of Src have been developed as anti-cancer drugs. Src is also implicated in acute inflammatory responses and osteoclast function. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|.
gi 530354652 177 IALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRVQD-KNGHEGYAPSSYL 226
Cdd:cd12008    3 VALYDYESRTETDLSFKKGERLQIVNNTEGDWWLAHSlTTGQTGYIPSNYV 53

Src homology 3 domain of Src-Like Adaptor Protein 2; SLAP2 plays a role in c-Cbl-dependent regulation of CSF1R, a tyrosine kinase important for myeloid cell growth and differentiation. It has been shown to interact with CSF1R, c-Cbl, LAT, CD247, and Zap70. SLAPs are adaptor proteins with limited similarity to Src family tyrosine kinases. They contain an N-terminal SH3 domain followed by an SH2 domain, and a unique C-terminal sequence. They function in regulating the signaling, ubiquitination, and trafficking of T-cell receptor (TCR) and B-cell receptor (BCR) components. The SH3 domain of SLAP forms a complex with v-Abl. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 177 IALYDYQTNDPQELALRCDEEYYLLdSSEIHWWRVQDK-NGHEGYAPSSY 225
Cdd:cd12011    3 VALCNFPSGGPTELSIRMGEQLTIL-SEDGDWWKVSSAvTGRECYIPSNY 51

Src homology 3 domain of Lck Protein Tyrosine Kinase; Lck is a member of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. Lck is expressed in T-cells and natural killer cells. It plays a critical role in T-cell maturation, activation, and T-cell receptor (TCR) signaling. Lck phosphorylates ITAM (immunoreceptor tyr activation motif) sequences on several subunits of TCRs, leading to the activation of different second messenger cascades. Phosphorylated ITAMs serve as binding sites for other signaling factor such as Syk and ZAP-70, leading to their activation and propagation of downstream events. In addition, Lck regulates drug-induced apoptosis by interfering with the mitochondrial death pathway. The apototic role of Lck is independent of its primary function in T-cell signaling. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 175 LVIALYDYQTNDPQELALRCDEEYYLLDSSEiHWWRVQD-KNGHEGYAPSSYL 226
Cdd:cd12005    1 LVVALYSYEPSHDGDLGFEKGEKLRILEQSG-EWWKAQSlTTGQEGFIPFNFV 52

Second C-terminal Src homology 3 domain of Dynamin Binding Protein, also called Tuba, and similar domains; DNMBP or Tuba is a cdc42-specific guanine nucleotide exchange factor (GEF) that contains four N-terminal SH3 domains, a central RhoGEF [or Dbl homology (DH)] domain followed by a Bin/Amphiphysin/Rvs (BAR) domain, and two C-terminal SH3 domains. It provides a functional link between dynamin, Rho GTPase signaling, and actin dynamics. It plays an important role in regulating cell junction configuration. The C-terminal SH3 domains of DNMBP bind to N-WASP and Ena/VASP proteins, which are key regulatory proteins of the actin cytoskeleton. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 178 ALYDYQTNDPQELALRCDEEYYLLDSSEI----HWWrVQDKNGHEGYAPSSYL 226
Cdd:cd12141    4 AVYTFKARSPNELSVSANQRVRILEFSDLtgnkEWW-LAEANGQKGYVPSNYI 55

C-terminal Src homology 3 domain of Growth factor receptor-bound protein 2; GRB2 is a critical signaling molecule that regulates the Ras pathway by linking tyrosine kinases to the Ras guanine nucleotide releasing protein Sos (son of sevenless), which converts Ras to the active GTP-bound state. It is ubiquitously expressed in all tissues throughout development and is important in cell cycle progression, motility, morphogenesis, and angiogenesis. In lymphocytes, GRB2 is associated with antigen receptor signaling components. GRB2 contains an N-terminal SH3 domain, a central SH2 domain, and a C-terminal SH3 domain. The C-terminal SH3 domain of GRB2 binds to Gab2 (Grb2-associated binder 2) through epitopes containing RxxK motifs, as well as to the proline-rich C-terminus of FGRF2. SH3 domains are protein interaction domains that typically bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRvQDKNGHEGYAPSSY 225
Cdd:cd11949    2 VQALFDFDPQEDGELGFRRGDFIEVMDNSDPNWWK-GACHGQTGMFPRNY 50

Src homology 3 domain of an unknown subfamily of proteins with similarity to Protein kinase C and Casein kinase Substrate in Neurons (PACSIN) proteins; PACSINs, also called Synaptic dynamin-associated proteins (Syndapins), act as regulators of cytoskeletal and membrane dynamics. They bind both dynamin and Wiskott-Aldrich syndrome protein (WASP), and may provide direct links between the actin cytoskeletal machinery through WASP and dynamin-dependent endocytosis. Vetebrates harbor three isoforms with distinct expression patterns and specific functions. PACSINs contain an N-terminal F-BAR domain and a C-terminal SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 176 VIALYDYQTNDPQELALRCDEEYYLL-DSSEIHW-WRVQDKnGHEGYAPSSYL 226
Cdd:cd11999    4 VRAVYDYTGQEPDELSFKAGEELLKVeDEDEQGWcKGVTDG-GAVGLYPANYV 55

Src Homology 3 domain of Rho GTPase-activating protein 27; Rho GTPase-activating proteins (RhoGAPs or ARHGAPs) bind to Rho proteins and enhance the hydrolysis rates of bound GTP. ARHGAP27, also called CAMGAP1, shows GAP activity towards Rac1 and Cdc42. It binds the adaptor protein CIN85 and may play a role in clathrin-mediated endocytosis. It contains SH3, WW, Pleckstin homology (PH), and RhoGAP domains. SH3 domains bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs; they play a role in the regulation of enzymes by intramolecular interactions, changing the subcellular localization of signal pathway components and mediate multiprotein complex assemblies.

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gi 530354652 175 LVIALYDYQTNDPQELALRCDEEYYLLDSSEIHWWRV-QDKNGHEGYAPSSYLVE 228
Cdd:cd12069    3 LVEHAFEYTGKDGRLVSIKPNERYILLRRTNEHWWHVrRDKGTRPFYIPAKYVKE 57

Src Homology 3 domain of Sorting Nexin 33; SNX33 interacts with Wiskott-Aldrich syndrome protein (WASP) and plays a role in the maintenance of cell shape and cell cycle progression. It modulates the shedding and endocytosis of cellular prion protein (PrP(c)) and amyloid precursor protein (APP). SNXs are Phox homology (PX) domain containing proteins that are involved in regulating membrane traffic and protein sorting in the endosomal system. SNX33 also contains BAR and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

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gi 530354652 178 ALYDYQTNDPQELALRCDEEYYLLDSSEIH-WWRVQDKNGHEGYAPSSYL 226
Cdd:cd11896    4 ALYSFQSENKEEINIQENEELVIFSENSLDgWLQGQNSRGETGLFPASYV 53