Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  152 PQTLHKVEQDPLELSCEVateTVQHTHLSVSWLRQKGGENPVevislsrdFILHSSSEYAQRQSLGEVRL--DKLGRSTF 229
Cdd:cd00099      5 PRSLSVQEGESVTLSCEV---SSSFSSTYIYWYRQKPGQGPE--------FLIYLSSSKGKTKGGVPGRFsgSRDGTSSF 73

                           90       100
                   ....*....|....*....|..
gi 1720405622  230 RLTIFHLQPSDQGEFYCEAAEW 251
Cdd:cd00099     74 SLTISNLQPEDSGTYYCAVSES 95

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 1720405622   16 VVSAQRQVTVQEGplyrtESSHITiwCNVSG---------YQGPSEQNFQWSIYLPSAPEREVQIVStvdssfpyaiytq 86
Cdd:cd00099      1 VTQSPRSLSVQEG-----ESVTLS--CEVSSsfsstyiywYRQKPGQGPEFLIYLSSSKGKTKGGVP------------- 60

                           90       100       110       120
                   ....*....|....*....|....*....|....*....|....*....
gi 1720405622   87 rvrgGKIYVERIQGNSALLHITDLQARDAGEYEC---HTPNTDERYFGS 132
Cdd:cd00099     61 ----GRFSGSRDGTSSFSLTISNLQPEDSGTYYCavsESGGTDKLTFGS 105

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  152 PQTLHKVEQDPLELSCEVateTVQHTHLSVSWLRQKGGENPVevislsrdFILHSSSEYAQRQSLGEVRL--DKLGRSTF 229
Cdd:cd00099      5 PRSLSVQEGESVTLSCEV---SSSFSSTYIYWYRQKPGQGPE--------FLIYLSSSKGKTKGGVPGRFsgSRDGTSSF 73

                           90       100
                   ....*....|....*....|..
gi 1720405622  230 RLTIFHLQPSDQGEFYCEAAEW 251
Cdd:cd00099     74 SLTISNLQPEDSGTYYCAVSES 95

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 1720405622  821 QVQGSLSVLETRQIQLECVVLNRTSVASQLlVEWFVWKPNHPEREVVAHlsrdATFHYGEQAAKNNLKGRlhaESPSSGV 900
Cdd:pfam07686    1 QTPREVTVALGGSVTLPCTYSSSMSEASTS-VYWYRQPPGKGPTFLIAY----YSNGSEEGVKKGRFSGR---GDPSNGD 72

                           90       100
                   ....*....|....*....|
gi 1720405622  901 YRLFIQNVAVQDSGTYSCRV 920
Cdd:pfam07686   73 GSLTIQNLTLSDSGTYTCAV 92

Immunoglobulin V-Type;

                            10        20        30        40        50        60        70        80
                    ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622   699 LNCSVKsqTSPNSHFAVLWYVHKPSDAdgkliLKTTHSSAFEYGTYAEEeGLRGRLQFERHVSGGLFSLTVQRAEVSDSG 778
Cdd:smart00406    4 LSCKFS--GSTFSSYYVSWVRQPPGKG-----LEWLGYIGSNGSSYYQE-SYKGRFTISKDTSKNDVSLTISNLRVEDTG 75

                    ....
gi 1720405622   779 SYYC 782
Cdd:smart00406   76 TYYC 79

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622   16 VVSAQRQVTVQEGplyrtESSHITiwCNVSG---------YQGPSEQNFQWSIYLPSAPEREVQIVStvdssfpyaiytq 86
Cdd:cd00099      1 VTQSPRSLSVQEG-----ESVTLS--CEVSSsfsstyiywYRQKPGQGPEFLIYLSSSKGKTKGGVP------------- 60

                           90       100       110       120
                   ....*....|....*....|....*....|....*....|....*....
gi 1720405622   87 rvrgGKIYVERIQGNSALLHITDLQARDAGEYEC---HTPNTDERYFGS 132
Cdd:cd00099     61 ----GRFSGSRDGTSSFSLTISNLQPEDSGTYYCavsESGGTDKLTFGS 105

Immunoglobulin Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins; The members here are composed of the Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins. CAR, which is encoded by human CXADR gene, is a cell adhesion molecule of the Immunoglobulin (Ig) superfamily. The CAR acts as a type I membrane receptor for group B1-B6 coxsackie viruses and subgroup C adenoviruses. For instance, adenovirus interacts with the coxsackievirus and adenovirus receptor to enter epithelial airway cells. The CAR is also shown to be involved in physiological processes such as neuronal and heart development, epithelial tight junction integrity, and tumor suppression. The CAR is a component of the epithelial apical junction complex that may function as a homophilic cell adhesion molecule and is essential for tight junction integrity. The CAR is also involved in transepithelial migration of leukocytes through adhesive interactions with JAML a transmembrane protein of the plasma membrane of leukocytes. The interaction between both receptors also mediates the activation of gamma-delta T-cells, a subpopulation of T-cells residing in epithelia and involved in tissue homeostasis and repair. The CAR is composed of one V-set and one C2-set Ig module, a single transmembrane helix, and an intracellular domain. This group belongs to the V-set of IgSF domains, having A, B, E and D strands in one beta-sheet and A', G, F, C, C' and C" in the other

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 1720405622  850 LLVEWFVWKPNHPEREVVAHLSRDATFHYGEqaaknNLKGRLHAESP-SSGVYRLFIQNVAVQDSGTYSCRV 920
Cdd:cd20960     34 LDIEWLLLPSDKVEKVVITYSGDRVYNHYYP-----ALKGRVAFTSNdLSGDASLNISNLKLSDTGTYQCKV 100

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 1720405622  294 VGEPVEFRcileAQNIPDRYFAVSWAFNSSLIATMGPNAVPvlnsdfahrEAKGQLKVAKESD-GVFVLKIYHLRQEDSG 372
Cdd:cd05775      9 LGGNVTLT----ISSLQDDIDEIKWKKTKDKIVEWENNIGP---------TYFGSFKDRVLLDkESGSLTIKNLTKEDSG 75

                           90
                   ....*....|....
gi 1720405622  373 KYNCRVTEREKTVT 386
Cdd:cd05775     76 TYELEITSTNGKVL 89

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  152 PQTLHKVEQDPLELSCEVateTVQHTHLSVSWLRQKGGENPVevislsrdFILHSSSEYAQRQSLGEVRL--DKLGRSTF 229
Cdd:cd00099      5 PRSLSVQEGESVTLSCEV---SSSFSSTYIYWYRQKPGQGPE--------FLIYLSSSKGKTKGGVPGRFsgSRDGTSSF 73

                           90       100
                   ....*....|....*....|..
gi 1720405622  230 RLTIFHLQPSDQGEFYCEAAEW 251
Cdd:cd00099     74 SLTISNLQPEDSGTYYCAVSES 95

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  685 SKRTLTLVENRAIQLNCSVksqTSPNSHFAVLWYVHKPSDADgKLILKTTHSSAFEygtyaeEEGLRGRLQFERHvSGGL 764
Cdd:cd00099      4 SPRSLSVQEGESVTLSCEV---SSSFSSTYIYWYRQKPGQGP-EFLIYLSSSKGKT------KGGVPGRFSGSRD-GTSS 72

                           90       100       110       120
                   ....*....|....*....|....*....|....*....|....*..
gi 1720405622  765 FSLTVQRAEVSDSGSYYChveewLLSPNYAWYKLaeeVSGR-TEVTV 810
Cdd:cd00099     73 FSLTISNLQPEDSGTYYC-----AVSESGGTDKL---TFGSgTRLTV 111

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 1720405622  151 VPQTLHKVEQDPLELSCEVATETVQHtHLSVSWLRQKGGENPVEVISLSrdfilHSSSEYAQRQSLGEVRLDKlGRSTFR 230
Cdd:pfam07686    2 TPREVTVALGGSVTLPCTYSSSMSEA-STSVYWYRQPPGKGPTFLIAYY-----SNGSEEGVKKGRFSGRGDP-SNGDGS 74

                           90
                   ....*....|....*.
gi 1720405622  231 LTIFHLQPSDQGEFYC 246
Cdd:pfam07686   75 LTIQNLTLSDSGTYTC 90

Immunoglobulin V-Type;

                            10        20        30        40        50        60        70        80
                    ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622   163 LELSCEVATETVQHTHlsVSWLRQKGGeNPVEVISlsrdFILHSSSEYAQRQSLGEVRLDK-LGRSTFRLTIFHLQPSDQ 241
Cdd:smart00406    2 VTLSCKFSGSTFSSYY--VSWVRQPPG-KGLEWLG----YIGSNGSSYYQESYKGRFTISKdTSKNDVSLTISNLRVEDT 74

                    ....*.
gi 1720405622   242 GEFYCE 247
Cdd:smart00406   75 GTYYCA 80

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 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" strands in the other.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622   16 VVSAQRQVTVQEGplyrtESSHITiwCNVSG---------YQGPSEQNFQWSIYLPSAPEREVQIVStvdssfpyaiytq 86
Cdd:cd00099      1 VTQSPRSLSVQEG-----ESVTLS--CEVSSsfsstyiywYRQKPGQGPEFLIYLSSSKGKTKGGVP------------- 60

                           90       100       110       120
                   ....*....|....*....|....*....|....*....|....*....
gi 1720405622   87 rvrgGKIYVERIQGNSALLHITDLQARDAGEYEC---HTPNTDERYFGS 132
Cdd:cd00099     61 ----GRFSGSRDGTSSFSLTISNLQPEDSGTYYCavsESGGTDKLTFGS 105

Immunoglobulin Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins; The members here are composed of the Variable (V) domain of the Coxsackievirus and Adenovirus Receptor (CAR), and similar proteins. CAR, which is encoded by human CXADR gene, is a cell adhesion molecule of the Immunoglobulin (Ig) superfamily. The CAR acts as a type I membrane receptor for group B1-B6 coxsackie viruses and subgroup C adenoviruses. For instance, adenovirus interacts with the coxsackievirus and adenovirus receptor to enter epithelial airway cells. The CAR is also shown to be involved in physiological processes such as neuronal and heart development, epithelial tight junction integrity, and tumor suppression. The CAR is a component of the epithelial apical junction complex that may function as a homophilic cell adhesion molecule and is essential for tight junction integrity. The CAR is also involved in transepithelial migration of leukocytes through adhesive interactions with JAML a transmembrane protein of the plasma membrane of leukocytes. The interaction between both receptors also mediates the activation of gamma-delta T-cells, a subpopulation of T-cells residing in epithelia and involved in tissue homeostasis and repair. The CAR is composed of one V-set and one C2-set Ig module, a single transmembrane helix, and an intracellular domain. This group belongs to the V-set of IgSF domains, having A, B, E and D strands in one beta-sheet and A', G, F, C, C' and C" in the other

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|..
gi 1720405622  850 LLVEWFVWKPNHPEREVVAHLSRDATFHYGEqaaknNLKGRLHAESP-SSGVYRLFIQNVAVQDSGTYSCRV 920
Cdd:cd20960     34 LDIEWLLLPSDKVEKVVITYSGDRVYNHYYP-----ALKGRVAFTSNdLSGDASLNISNLKLSDTGTYQCKV 100

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) beta chain; The members here are composed of the immunoglobulin (Ig) variable domain of the beta chain of alpha/beta T-cell antigen receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta, polypeptide chains with variable (V) and constant (C) regions. This group includes the variable domain of the alpha chain of alpha/beta TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  682 VSKSKRTLTLVENRAIQLNCSVKSQtspnsHFAVLWYVHKPSDADgKLILKTTHSSAFEYGTYAEEeglrgRLQFERHvS 761
Cdd:cd05899      1 VTQSPRYLIKRRGQSVTLRCSQKSG-----HDNMYWYRQDPGKGL-QLLFYSYGGGLNEEGDLPGD-----RFSASRP-S 68

                           90       100
                   ....*....|....*....|.
gi 1720405622  762 GGLFSLTVQRAEVSDSGSYYC 782
Cdd:cd05899     69 LTRSSLTIKSAEPEDSAVYLC 89

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  679 KLQVSKSKRTLTLVENRAIQLNCSVKSQTSPNshfaVLWYVhkpsdaDGKLILKTTHSSAFEYGTYAeeeglrgrlqfer 758
Cdd:pfam13927    1 KPVITVSPSSVTVREGETVTLTCEATGSPPPT----ITWYK------NGEPISSGSTRSRSLSGSNS------------- 57

                           90       100
                   ....*....|....*....|....*..
gi 1720405622  759 hvsgglfSLTVQRAEVSDSGSYYCHVE 785
Cdd:pfam13927   58 -------TLTISNVTRSDAGTYTCVAS 77

Immunoglobulin variable (IgV)-like domain in complement receptor of the immunoglobulin superfamily (CRIg); The members here are composed of the immunoglobulin variable (IgV) region of the complement receptor of the immunoglobulin superfamily (CRIg). The N-terminal domain of CRIg (also known as Z39Ig and V-set and Ig domain-containing 4 (VSIG4) belongs to the IgV family of immunoglobulin-like domains while the C-terminal domain of CRIg belongs to the IgC family of immunoglobulin-like domains. Like all members of this family, the CRIg domain contains two beta-sheets: one composed of strands A', G, F, C, C' and C", and the other of strands B, E and D. The complement system is an important part of the innate immune system and is required for removal of pathogens from the bloodstream. After exposure to pathogens, the third component of the complement system, C3, is cleaved to C3b which, after recruitment of factor B, initiates formation of the alternative pathway convertases. CRIg, a complement receptor expressed on macrophages, binds to C3b and iC3b mediating phagocytosis of the particles. It is also a potent inhibitor of the alternative pathway convertases and a negative regulator of T cell activation. 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, such as, T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, such as, 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.

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|...
gi 1720405622  848 SQLLVEWFVWKPNHPerevVAHLSRDATfhyGEQAAKNNLKGRLHAESPSSGVYRLFIQNVAVQDSGTYSCRV 920
Cdd:cd16089     30 TQVLVKWLVQRDSDP----VTIFLRDSS---GDHIQQAKYRGRLEVSKDTPGDVSLQLDTLEMDDRGHYTCQV 95

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) alpha chain and similar proteins; The members here are composed of the immunoglobulin (Ig) variable domain of the alpha chain of alpha/beta T-cell antigen receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta polypeptide chains with variable (V) and constant (C) regions. This group represents the variable domain of the alpha chain of TCRs and also includes the variable domain of delta chains of TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  821 QVQGSLSVLETRQIQLECvvlNRTSVASQLLvEWFVWKPN-HPErevvaHLSRdATFHYGEQAaknnlKGRLHAE-SPSS 898
Cdd:cd04983      3 QSPQSLSVQEGENVTLNC---NYSTSTFYYL-FWYRQYPGqGPQ-----FLIY-ISSDSGNKK-----KGRFSATlDKSR 67

                           90       100       110
                   ....*....|....*....|....*....|....*
gi 1720405622  899 GVYRLFIQNVAVQDSGTYSCRVeewlpSPSGVWYK 933
Cdd:cd04983     68 KSSSLHISAAQLSDSAVYFCAL-----SESGGTGK 97

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

                            10        20        30        40        50        60        70        80
                    ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622   293 TVGEPVEFRCILEAQNIPDryfaVSWAFNssliatmgpNAVPVLNSDFAHreakgqlkvAKESDGVFVLKIYHLRQEDSG 372
Cdd:smart00410    7 KEGESVTLSCEASGSPPPE----VTWYKQ---------GGKLLAESGRFS---------VSRSGSTSTLTISNVTPEDSG 64

                            90
                    ....*....|....*..
gi 1720405622   373 KYNCRVTEREKTVTGEF 389
Cdd:smart00410   65 TYTCAATNSSGSASSGT 81

Immunoglobulin (Ig)-like variable (V) domain of Cluster of Differentiation (CD) 8 alpha chain; The members here are composed of the immunoglobulin (Ig)-like variable domain of the Cluster of Differentiation (CD) 8 alpha. The CD8 glycoprotein plays an essential role in the control of T-cell selection, maturation, and the T-cell receptor (TCR)-mediated response to peptide antigen. CD8 is comprised of alpha and beta subunits and is expressed as either an alpha/alpha or alpha/beta dimer. Both dimeric isoforms can serve as a coreceptor for T cell activation and differentiation, however they have distinct physiological roles, different cellular distributions, unique binding partners, etc. Each CD8 subunit is comprised of an extracellular domain containing a V-type Ig-like domain, a single pass transmembrane portion, and a short intracellular domain. The Ig domain of CD8 alpha binds to antibodies. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1720405622  152 PQTLHKVEQDPLELSCEVATETVQhthlSVSWLRQKGGENPVEVislsrdFILHSSSeyAQRQSLGEvRLD-------KL 224
Cdd:cd05720      5 PRKRDAQLGQKVELVCEVLNSVPQ----GCSWLFQPRGSAPQPT------FLLYLSS--SNKTKWAE-GLDskrfsgsRS 71

                           90       100
                   ....*....|....*....|....*
gi 1720405622  225 GrSTFRLTIFHLQPSDQGEFYCEAA 249
Cdd:cd05720     72 G-SSYVLTLKDFRKEDEGYYFCSVI 95