Immunoglobulin domain; The members here are composed of the immunoglobulin (Ig) domain found in the Ig superfamily. The Ig superfamily is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. Members of this group are components of immunoglobulin, neuroglia, cell surface glycoproteins, including T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, including butyrophilin and chondroitin sulfate proteoglycan core protein. A predominant feature of most Ig domains is a disulfide bridge connecting the two beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E, and D strands in one sheet and A', G, F, C, C' and C" in the other. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other by strands G, F, C, and C'. Moreover, a C1-set Ig domain contains a short C' strand (three residues) and lacks A' and C" strand. Unlike other Ig domain sets, C2-set structures do not have a D strand. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  146 QPSLQVTN-TTVKELDSVTLTCLSKDRQAHIHWIFNNDTLLITEKMTTSQAGLILKIDPIKREDAGEYQCEISNPVSVKR 224
Cdd:cd05740   1 KPFISSNNsNPVEDKDAVTLTCEPETQNTSYLWWFNGQSLPVTPRLTLSNGNRTLTLLNVTREDAGAYQCEISNPVSANR 80

                ....*....
gi 6671734  225 SNSIKLEVI 233
Cdd:cd05740  81 SDPVTLDVI 89

Immunoglobulin (Ig)-like domain of human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) domains 2, 4, and 6, and similar domains; The members here are composed of the second, fourth, and sixth immunoglobulin (Ig)-like domains in human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) protein subfamily. The CEA family is a group of anchored or secreted glycoproteins expressed by epithelial cells, leukocytes, endothelial cells, and placenta. The CEA family is divided into the CEACAM and pregnancy-specific glycoprotein (PSG) subfamilies. This group represents the CEACAM subfamily. CEACAM1 has many important cellular functions; it is a cell adhesion molecule and a signaling molecule that regulates the growth of tumor cells, an angiogenic factor, and a receptor for bacterial and viral pathogens, including mouse hepatitis virus (MHV). In mice, four isoforms of CEACAM1 generated by alternative splicing have either two [D1, D4] or four [D1-D4] Ig-like domains on the cell surface.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  146 QPSLQVTN-TTVKELDSVTLTCLSKDRQAHIHWIFNNDTLLITEKMTTSQAGLILKIDPIKREDAGEYQCEISNPVSVKR 224
Cdd:cd05740   1 KPFISSNNsNPVEDKDAVTLTCEPETQNTSYLWWFNGQSLPVTPRLTLSNGNRTLTLLNVTREDAGAYQCEISNPVSANR 80

                ....*....
gi 6671734  225 SNSIKLEVI 233
Cdd:cd05740  81 SDPVTLDVI 89

Immunoglobulin like; IG domains that cannot be classified into one of IGv1, IGc1, IGc2, IG.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734     153 NTTVKELDSVTLTC-LSKDRQAHIHWIFNNDTLLITE---KMTTSQAGLILKIDPIKREDAGEYQCEISNPvSVKRSNSI 228
Cdd:smart00410   3 SVTVKEGESVTLSCeASGSPPPEVTWYKQGGKLLAESgrfSVSRSGSTSTLTISNVTPEDSGTYTCAATNS-SGSASSGT 81

                   ....
gi 6671734     229 KLEV 232
Cdd:smart00410  82 TLTV 85

Immunoglobulin (Ig)-like domain of human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) domains 2, 4, and 6, and similar domains; The members here are composed of the second, fourth, and sixth immunoglobulin (Ig)-like domains in human carcinoembryonic antigen (CEA) related cell adhesion molecule (CEACAM) protein subfamily. The CEA family is a group of anchored or secreted glycoproteins expressed by epithelial cells, leukocytes, endothelial cells, and placenta. The CEA family is divided into the CEACAM and pregnancy-specific glycoprotein (PSG) subfamilies. This group represents the CEACAM subfamily. CEACAM1 has many important cellular functions; it is a cell adhesion molecule and a signaling molecule that regulates the growth of tumor cells, an angiogenic factor, and a receptor for bacterial and viral pathogens, including mouse hepatitis virus (MHV). In mice, four isoforms of CEACAM1 generated by alternative splicing have either two [D1, D4] or four [D1-D4] Ig-like domains on the cell surface.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  146 QPSLQVTN-TTVKELDSVTLTCLSKDRQAHIHWIFNNDTLLITEKMTTSQAGLILKIDPIKREDAGEYQCEISNPVSVKR 224
Cdd:cd05740   1 KPFISSNNsNPVEDKDAVTLTCEPETQNTSYLWWFNGQSLPVTPRLTLSNGNRTLTLLNVTREDAGAYQCEISNPVSANR 80

                ....*....
gi 6671734  225 SNSIKLEVI 233
Cdd:cd05740  81 SDPVTLDVI 89

Immunoglobulin V-set domain; This domain is found in antibodies as well as neural protein P0 and CTL4 amongst others.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734     42 PLHAAEGNNVILVV---YNMMKGVSAFSWHKGST-TSTNAEIVRFVTGTNKTIKGPVHSGRETL-YSNGSLLIQRVTMKD 116
Cdd:pfam07686   5 EVTVALGGSVTLPCtysSSMSEASTSVYWYRQPPgKGPTFLIAYYSNGSEEGVKKGRFSGRGDPsNGDGSLTIQNLTLSD 84

                          90       100
                  ....*....|....*....|....*
gi 6671734    117 TGVYTIEMTDQNYRRRVLTGQFHVH 141
Cdd:pfam07686  85 SGTYTCAVIPSGEGVFGKGTRLTVL 109

Immunoglobulin domain; Members of the immunoglobulin superfamily are found in hundreds of proteins of different functions. Examples include antibodies, the giant muscle kinase titin and receptor tyrosine kinases. Immunoglobulin-like domains may be involved in protein-protein and protein-ligand interactions.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734    152 TNTTVKELDSVTLTCLSKDR--QAHIHWIFNNDTLLITEKMTTSQAGLI---LKIDPIKREDAGEYQCEISNPVSVKRSN 226
Cdd:pfam00047   4 PTVTVLEGDSATLTCSASTGspGPDVTWSKEGGTLIESLKVKHDNGRTTqssLLISNVTKEDAGTYTCVVNNPGGSATLS 83

                  ..
gi 6671734    227 SI 228
Cdd:pfam00047  84 TS 85

Immunoglobulin domain; The members here are composed of the immunoglobulin (Ig) domain found in the Ig superfamily. The Ig superfamily is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. Members of this group are components of immunoglobulin, neuroglia, cell surface glycoproteins, including T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, including butyrophilin and chondroitin sulfate proteoglycan core protein. A predominant feature of most Ig domains is a disulfide bridge connecting the two beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E, and D strands in one sheet and A', G, F, C, C' and C" in the other. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other by strands G, F, C, and C'. Moreover, a C1-set Ig domain contains a short C' strand (three residues) and lacks A' and C" strand. Unlike other Ig domain sets, C2-set structures do not have a D strand. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  162 VTLTCLSK-DRQAHIHWIFNNDTLL--ITEKMTTSQAGLILKIDPIKREDAGEYQCEISNPVSVKRSNSI 228
Cdd:cd00096   1 VTLTCSASgNPPPTITWYKNGKPLPpsSRDSRRSELGNGTLTISNVTLEDSGTYTCVASNSAGGSASASV 70

agrin-responsive first immunoglobulin-like domains (Ig1) of the MuSK ectodomain; a member of the I-set of IgSF domains; The members here are composed of the first immunoglobulin-like domains (Ig1) of the Muscle-specific kinase (MuSK). MuSK is a receptor tyrosine kinase specifically expressed in skeletal muscle, where it plays a central role in the formation and maintenance of the neuromuscular junction (NMJ). MuSK is activated by agrin, a neuron-derived heparan sulfate proteoglycan. The activation of MUSK in myotubes regulates the formation of NMJs through the regulation of different processes including the specific expression of genes in subsynaptic nuclei, the reorganization of the actin cytoskeleton and the clustering of the acetylcholine receptors (AChR) in the postsynaptic membrane. The Ig superfamily (IgSF) is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Unlike the V-set, one of the distinctive features of I-set domains is the lack of a C" strand. The structure of the MuSK lacks this strand and thus it belongs to the I-set of the IgSF. I-set domains are found in several cell adhesion molecules (such as VCAM, ICAM, and MADCAM), and are also present in numerous other diverse protein families, including several tyrosine-protein kinase receptors, the hemolymph protein hemolin, the muscle proteins titin, telokin, and twitchin, the neuronal adhesion molecule axonin-1, and the signaling molecule semaphorin 4D that is involved in axonal guidance, immune function and angiogenesis.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  143 PVTQPSLQVTNTTVKELDSVTLTCL-SKDRQAHIHWiFNNDTLLIT--EKMTTSQAGLILKIDPIKREDAGEYQCEISNP 219
Cdd:cd20970   1 PVISTPQPSFTVTAREGENATFMCRaEGSPEPEISW-TRNGNLIIEfnTRYIVRENGTTLTIRNIRRSDMGIYLCIASNG 79

                        90
                ....*....|...
gi 6671734  220 VSVKRSNSIKLEV 232
Cdd:cd20970  80 VPGSVEKRITLQV 92

N-terminal immunoglobulin (Ig)-like domain of T-cell surface antigen CD2, and similar domains; The members here are composed of the N-terminal immunoglobulin (Ig)-like domain (or domain 1) of T-cell surface antigen Clusters of Differentiation (CD) 2 and similar proteins. CD2 is a T-cell specific surface glycoprotein and is critically important for mediating adhesion between T cells and antigen-presenting cells or between cytolytic T cells and target cells. CD2 is located on chromosome 1 at 1p13 in humans and on chromosome 3 in mice. CD2 contains an extracellular domain with two or Ig-like domains, a single transmembrane segment, and a cytoplasmic region rich in proline and basic residues.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734   45 AAEGNNVILVVYNMMKGVSAFSWHKGSTtstnaEIVRFVTGTNKTIKGPVhSGRETL-YSNGSLLIQRVTMKDTGVYTIE 123
Cdd:cd05775   7 GALGGNVTLTISSLQDDIDEIKWKKTKD-----KIVEWENNIGPTYFGSF-KDRVLLdKESGSLTIKNLTKEDSGTYELE 80

                ....*
gi 6671734  124 MTDQN 128
Cdd:cd05775  81 ITSTN 85

Third immunoglobulin (Ig)-like domain of hemolin, and similar domains; a member of the I-set of IgSF domains; The members here are composed of the third immunoglobulin (Ig)-like domain of hemolin and similar proteins. Hemolin, an insect immunoglobulin superfamily (IgSF) member containing four Ig-like domains, is a lipopolysaccharide-binding immune protein induced during bacterial infection. Hemolin shares significant sequence similarity with the first four Ig-like domains of the transmembrane cell adhesion molecules (CAMs) of the L1 family. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. The third Ig-like domain of hemolin is a member of the I-set Ig domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand but lack a C" strand. I-set domains are found in several cell adhesion molecules, including vascular (VCAM), intercellular (ICAM), neural (NCAM) and mucosal addressin (MADCAM) cell adhesion molecules, as well as junction adhesion molecules (JAM).

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  143 PVTQPSLQvtNTTVKELDSVTLTCLSKDR-QAHIHWIFN------NDTLLITEKMTTSQAGLILKidPIKREDAGEYQCE 215
Cdd:cd20977   1 PVPQYVSK--DMMAKAGDVTMIYCMYGSNpTAHPNYFKNgkdvngNPEDRITRHNRTSGKRLLFK--TTLPEDEGVYTCE 76

                        90
                ....*....|....*..
gi 6671734  216 ISNPVSVKRSNSIKLEV 232
Cdd:cd20977  77 VDNGVGKPQKHSLKLTV 93

Third immunoglobulin domain in Cluster of Differentiation (CD) 22; member of the Constant 2 (C2)-set of IgSF domains; The members here are composed of the third immunoglobulin domain in Cluster of Differentiation (CD) 22 (also known as Siglec-2). CD22, a sialic-acid binding immunoglobulin type-lectin (Siglec) family member, is an inhibitory co-receptor of the B-cell receptor (BCR). The inhibitory function of CD22 and its restricted expression on B cells makes CD22 an attractive target against dysregulated B cells that cause autoimmune diseases and B-cell-derived cancers. CD22 plays a vital role in establishing a baseline level of B-cell inhibition, and thus is an important determinant of homeostasis in humoral immunity. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are organized as an extracellular module composed of Ig-like domains (an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains), followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. IgSF domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. This group belongs to the C2-set of IgSF domains, having A, B, and E strands in one beta-sheet and A', G, F, C' in the other. Unlike other Ig domain sets, the C2-set lacks the D strand.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  147 PSLQV----TNTTVKELDSVTLTC---LSKDRQAHIHWIFNNDTLlitekmtTSQAGLILKIDPIKREDAGEYQCEISNP 219
Cdd:cd20937   1 PKLEIkvtpSDAIVREGDSVTMTCevsSSNPEYTTVSWLKDGTSL-------KKQNTFTLNLREVTKDQSGKYCCQVSND 73

                        90
                ....*....|....*
gi 6671734  220 VSVKRSNSIKLEVIF 234
Cdd:cd20937  74 VGPGRSEEVFLQVQY 88

First immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the first immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 6671734  154 TTVKELDSVTLTC--LSKDRQAHIHWiFNNDTLLitEKMTTSqagliLKIDPIKREDAGEYQCEISNpvsVKRSNSIKLE 231
Cdd:cd05752  10 TTVFQGEKVTLTCqgFYSPEQNSTQW-YHNGTLI--SSTSSS-----YRIVAATVNDSGEYRCQTQG---SSLSDPVHLE 78

                .
gi 6671734  232 V 232
Cdd:cd05752  79 V 79

Second immunoglobulin (Ig)-like domain in Robo (roundabout) receptors; member of the I-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin (Ig)-like domain in Robo (roundabout) receptors. Robo receptors play a role in the development of the central nervous system (CNS), and are receptors of the Slit protein. Slit is a repellant secreted by the neural cells in the midline. Slit acts through Robo to prevent most neurons from crossing the midline from either side. Three mammalian Robo homologs (Robo1, Robo2, and Robo3), and three mammalian Slit homologs (Slit-1,Slit-2, Slit-3), have been identified. Commissural axons, which cross the midline, express low levels of Robo; longitudinal axons, which avoid the midline, express high levels of Robo. Robo1, Robo2, and Robo3 are expressed by commissural neurons in the vertebrate spinal cord and Slit-1, Slit-2, Slit-3 are expressed at the ventral midline. Robo-3 is a divergent member of the Robo family which instead of being a positive regulator of Slit responsiveness, antagonizes Slit responsiveness in precrossing axons. The Slit-Robo interaction is mediated by the second leucine-rich repeat (LRR) domain of Slit and the two N-terminal Ig domains of Robo, Ig1 and Ig2. The primary Robo binding site for Slit-2 has been shown by surface plasmon resonance experiments and mutational analysis to be the Ig1 domain, while the Ig2 domain has been proposed to harbor a weak secondary binding site. This group belongs to the I-set of IgSF domains, having A-B-E-D strands in one beta-sheet and A'-G-F-C-C' in the other. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                        10        20        30        40        50
                ....*....|....*....|....*....|....*....|....*....|....*...
gi 6671734  175 IHWIFNNDTLLITEKMTTSQAGLILKIDPIKREDAGEYQCEISNPVSVKRSNSIKLEV 232
Cdd:cd05724  30 VSWRKDGQPLNLDNERVRIVDDGNLLIAEARKSDEGTYKCVATNMVGERESRAARLSV 87

Immunoglobulin (Ig)-like domain of class III semaphorin Sema3; The members here are composed of the immunoglobulin (Ig)-like domain of Sema3 and similar proteins. Semaphorins are classified based on structural features additional to the Sema domain. Sema3 is a Class III semaphorin that is secreted. It is a vertebrate class having a Sema domain, an Ig domain, a short basic domain. They have been shown to be axonal guidance cues and have a part in the regulation of the cardiovascular, immune, and respiratory systems. Sema3A, the prototype member of this class III subfamily, induces growth cone collapse and is an inhibitor of axonal sprouting. In perinatal rat cortex, it acts as a chemoattractant and functions to direct the orientated extension of apical dendrites. It may play a role, prior to the development of apical dendrites, in signaling the radial migration of newborn cortical neurons towards the upper layers. Sema3A selectively inhibits vascular endothelial growth factor receptor (VEGF)-induced angiogenesis and induces microvascular permeability. This group also includes Sema3B, -C, -D, -E, -G.

                        10        20        30        40        50        60
                ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 6671734   74 STNAEIVRFVTGTNKTIKGPVHSGRETLYSNGSLLIQRVTMKDTGVYTIEMTDQNYRRRVLTGQFHV 140
Cdd:cd05871  23 SPQATVKWLFQRGGDQRKEEVKSEERLIVTDRGLLLRSLQRSDAGVYTCQAVEHGFSQTLVKIRLHV 89