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 48425197   3 QLQESGPGLVAPSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWLGVIW-GDGITDYNSALKSRLSVTKDNSKSQVFLK 81
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90       100       110
                ....*....|....*....|....*....|....*...
gi 48425197  82 MNSLQSGDSARYYCVTGL-------FDYWGQGTTLTVS 112
Cdd:cd04981  81 LNSLTSEDTAVYYCARGLggygysyFDYWGQGTTVTVS 118

Immunoglobulin (Ig) heavy chain (H), variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. 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. There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which can associate with any of the heavy chains. This family includes alpha, gamma, delta, epsilon, and mu heavy chains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197   3 QLQESGPGLVAPSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWLGVIW-GDGITDYNSALKSRLSVTKDNSKSQVFLK 81
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90       100       110
                ....*....|....*....|....*....|....*...
gi 48425197  82 MNSLQSGDSARYYCVTGL-------FDYWGQGTTLTVS 112
Cdd:cd04981  81 LNSLTSEDTAVYYCARGLggygysyFDYWGQGTTVTVS 118

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 48425197     5 QESGPGLVAPSQSLSITCTVSGFSLTD-YGVNWVRQSPGKGLEWLGVIWGDGITdyNSALKSRLSVTKDNSKSQVFLKMN 83
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSSSMSEAsTSVYWYRQPPGKGPTFLIAYYSNGSE--EGVKKGRFSGRGDPSNGDGSLTIQ 78

                          90       100       110
                  ....*....|....*....|....*....|
gi 48425197    84 SLQSGDSARYYCVTGLFD--YWGQGTTLTV 111
Cdd:pfam07686  79 NLTLSDSGTYTCAVIPSGegVFGKGTRLTV 108

Immunoglobulin (Ig) heavy chain (H), variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. 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. There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which can associate with any of the heavy chains. This family includes alpha, gamma, delta, epsilon, and mu heavy chains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197   3 QLQESGPGLVAPSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWLGVIW-GDGITDYNSALKSRLSVTKDNSKSQVFLK 81
Cdd:cd04981   1 QLQESGPGLVKPGQSLKLSCKASGFTFTSYGMGWVRQAPGKGLEWIGLIYpGGGDTYYADSFKGRFTITRDTSKSTAYLQ 80

                        90       100       110
                ....*....|....*....|....*....|....*...
gi 48425197  82 MNSLQSGDSARYYCVTGL-------FDYWGQGTTLTVS 112
Cdd:cd04981  81 LNSLTSEDTAVYYCARGLggygysyFDYWGQGTTVTVS 118

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 48425197   5 QESGPGLVAPSQSLSITCTVSGFSLTDYgVNWVRQSPGKGLEWLgVIWGDGITDYNSALKSRLSVTKDnSKSQVFLKMNS 84
Cdd:cd00099   3 QSPRSLSVQEGESVTLSCEVSSSFSSTY-IYWYRQKPGQGPEFL-IYLSSSKGKTKGGVPGRFSGSRD-GTSSFSLTISN 79

                        90       100       110
                ....*....|....*....|....*....|..
gi 48425197  85 LQSGDSARYYCVTGLFD-----YWGQGTTLTV 111
Cdd:cd00099  80 LQPEDSGTYYCAVSESGgtdklTFGSGTRLTV 111

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) gamma chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the gamma chain of gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigens as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain the standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197  13 APSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWLGVIWGDGITDYNSAL-KSRLSVTKDNSKSQVFLKMNSLQSGDSA 91
Cdd:cd04982  11 EESKSVTISCKVSGIDFSTTYIHWYRQKPGQALERLLYVSSTSAVRKDSGKtKNKFEARKDVGKSTSTLTITNLEKEDSA 90

                        90       100
                ....*....|....*....|....*..
gi 48425197  92 RYYCVTGLFD--YW----GQGTTLTVS 112
Cdd:cd04982  91 TYYCAYWESGsgYYikvfGSGTKLIVT 117

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 48425197   5 QESGPGLVAPSQSLSITCTVSgfSLTDYGVNWVRQSPGKGLEWLGVIwgdgITDYNSALKSRLSVTKDNSKSQVFLKMNS 84
Cdd:cd04983   3 QSPQSLSVQEGENVTLNCNYS--TSTFYYLFWYRQYPGQGPQFLIYI----SSDSGNKKKGRFSATLDKSRKSSSLHISA 76

                        90       100       110
                ....*....|....*....|....*....|..
gi 48425197  85 LQSGDSARYYC-VTGLFDYW----GQGTTLTV 111
Cdd:cd04983  77 AQLSDSAVYFCaLSESGGTGkltfGKGTRLTV 108

T-cell receptor Mu, Heavy chain, variable (V) domain; The members here are composed of the immunoglobulin (Ig) heavy chain (H), variable (V) domain of the T-cell receptor Mu. 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. There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which can associate with any of the heavy chains. This family includes alpha, gamma, delta, epsilon, and mu heavy chains. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197   3 QLQESGPGLVAPSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWLGVIwgdgitDYNSALKS--RLSVTKDNSKSQVFL 80
Cdd:cd16095   3 QLEESGGGSHPAGKTLSLKCQTSGFQFNTSQLSWYLWVPGHAPLWLTSL------DHISTKVSedRITSSREDTNSQIFL 76

                        90
                ....*....|....*.
gi 48425197  81 KMNSLQSGDSARYYCV 96
Cdd:cd16095  77 QIKGLGLRDSGQYHCA 92

Immunoglobulin (Ig) variable (V) domain of Cluster of Differentiation (CD) 8 beta chain; The members here are composed of the immunoglobulin (Ig)-like domain in Cluster of Differentiation (CD) 8 beta. 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. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197   4 LQESGPGLVAPSQSLSITCTVSGFsLTDYGVNWVRQ----SPGKGLEWL-------GVIWGDGITdynsalKSRLSVTKD 72
Cdd:cd07700   2 LQTPGSLLVQTNQTVKMSCEAKTS-PKNTRIYWLRQrqapSKDSHFEFLaswdpskGIVYGEGVD------QEKLIILSD 74

                        90       100       110       120
                ....*....|....*....|....*....|....*....|....
gi 48425197  73 NSKSQVFLKMNSLQSGDSARYYCVTG-----LFdywGQGTTLTV 111
Cdd:cd07700  75 SDSSRYILSLMSVKPEDSGTYFCMTVgspelIF---GTGTKLSV 115

Gammadelta T-cell antigen receptor, variable (V) domain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing, and MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 48425197  12 VAPSQSLSITCTVSGFSLTDYGVNWVRQSPGKGLEWlgvIWGDGITdYNSALKSRLSVTKDNSKSQVFLKMNSLQSGDSA 91
Cdd:cd20988  10 VSVGKPVTLKCSMKGEAISNYYINWYRKTQGNTMTF---IYREGGI-YGPGFKDNFRGDIDSSNNLAVLKILEASERDEG 85

                        90       100
                ....*....|....*....|....*...
gi 48425197  92 RYYCV---TGLFDY-----WGQGTTLTV 111
Cdd:cd20988  86 SYYCAsdtPGGGREydpliFGKGTYLTV 113