Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, 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. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). 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 seem to be functionally identical, and can associate with any of the heavy chains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794     2 VVMTQTPLSLPVSLGDQASISCRSSQSLvhsnGNTYLNWYLQKAGQSPKLLIYKVSNRFSGVPDRFSGSGSGTDFTLKIS 81
Cdd:cd04980   1 IVMTQSPASLSVSPGERVTISCKASQSI----SSNYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTIS 76

                        90       100       110
                ....*....|....*....|....*....|
gi 125794    82 RVEAEDLGIYFCSQTTHVPPTFGGGTKLEI 111
Cdd:cd04980  77 SVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, 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. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). 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 seem to be functionally identical, and can associate with any of the heavy chains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794     2 VVMTQTPLSLPVSLGDQASISCRSSQSLvhsnGNTYLNWYLQKAGQSPKLLIYKVSNRFSGVPDRFSGSGSGTDFTLKIS 81
Cdd:cd04980   1 IVMTQSPASLSVSPGERVTISCKASQSI----SSNYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTIS 76

                        90       100       110
                ....*....|....*....|....*....|
gi 125794    82 RVEAEDLGIYFCSQTTHVPPTFGGGTKLEI 111
Cdd:cd04980  77 SVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794       19 ASISCRSSQSlvhSNGNTYLNWYLQKAGQSPKLLIYKVSNR----FSGVPDRFSGSG--SGTDFTLKISRVEAEDLGIYF 92
Cdd:smart00406   2 VTLSCKFSGS---TFSSYYVSWVRQPPGKGLEWLGYIGSNGssyyQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTYY 78

                   ...
gi 125794       93 CSQ 95
Cdd:smart00406  79 CAV 81

Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, 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. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). 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 seem to be functionally identical, and can associate with any of the heavy chains.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794     2 VVMTQTPLSLPVSLGDQASISCRSSQSLvhsnGNTYLNWYLQKAGQSPKLLIYKVSNRFSGVPDRFSGSGSGTDFTLKIS 81
Cdd:cd04980   1 IVMTQSPASLSVSPGERVTISCKASQSI----SSNYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTIS 76

                        90       100       110
                ....*....|....*....|....*....|
gi 125794    82 RVEAEDLGIYFCSQTTHVPPTFGGGTKLEI 111
Cdd:cd04980  77 SVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

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 125794     4 MTQTPLSLPVSLGDQASISCRSSQSlvhsNGNTYLNWYLQKAGQSPKLLIYKVSNRFS---GVPDRFSGSGSG-TDFTLK 79
Cdd:cd00099   1 VTQSPRSLSVQEGESVTLSCEVSSS----FSSTYIYWYRQKPGQGPEFLIYLSSSKGKtkgGVPGRFSGSRDGtSSFSLT 76

                        90       100       110
                ....*....|....*....|....*....|....*
gi 125794    80 ISRVEAEDLGIYFCSQT---THVPPTFGGGTKLEI 111
Cdd:cd00099  77 ISNLQPEDSGTYYCAVSesgGTDKLTFGSGTRLTV 111

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 125794     5 TQTPLSLPVSLGDQASISCRssqslvHSNGNTYLNWYLQKAGQSPKLLIY---KVSNRFSGVP-DRFSGSG-SGTDFTLK 79
Cdd:cd05899   2 TQSPRYLIKRRGQSVTLRCS------QKSGHDNMYWYRQDPGKGLQLLFYsygGGLNEEGDLPgDRFSASRpSLTRSSLT 75

                        90       100       110
                ....*....|....*....|....*....|...
gi 125794    80 ISRVEAEDLGIYFC---SQTTHVPPTFGGGTKL 109
Cdd:cd05899  76 IKSAEPEDSAVYLCassLGGGADEAYFGPGTRL 108

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 125794     5 TQTPLSLPVSLGDQASISCRSSQSlvhsnGNTYLNWYLQKAGQSPKLLIYKVSN-------RFSGVPDRFSGSgsgtdFT 77
Cdd:cd04983   2 TQSPQSLSVQEGENVTLNCNYSTS-----TFYYLFWYRQYPGQGPQFLIYISSDsgnkkkgRFSATLDKSRKS-----SS 71

                        90       100       110
                ....*....|....*....|....*....|....*...
gi 125794    78 LKISRVEAEDLGIYFCSQTTHVP---PTFGGGTKLEIK 112
Cdd:cd04983  72 LHISAAQLSDSAVYFCALSESGGtgkLTFGKGTRLTVE 109

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 125794     4 MTQTPLSLPVSLGDQASISCRSSqslVHSNGNTYLNWYLQKAGQSPKLLIY------------KVSNRFSgvPDRFSGSG 71
Cdd:cd04982   1 LEQPQLSITREESKSVTISCKVS---GIDFSTTYIHWYRQKPGQALERLLYvsstsavrkdsgKTKNKFE--ARKDVGKS 75

                        90       100       110       120
                ....*....|....*....|....*....|....*....|..
gi 125794    72 SgtdFTLKISRVEAEDLGIYFC----SQTTHVPPTFGGGTKL 109
Cdd:cd04982  76 T---STLTITNLEKEDSATYYCayweSGSGYYIKVFGSGTKL 114

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 125794    10 SLPVSLGDQASISCRSSQSLVhsnGNTYLNWYlQKAGQSPKLLIYKVSNRFS-GVPDRFSGS--GSGTDFTLKISRVEAE 86
Cdd:cd20988   7 TVTVSVGKPVTLKCSMKGEAI---SNYYINWY-RKTQGNTMTFIYREGGIYGpGFKDNFRGDidSSNNLAVLKILEASER 82

                        90       100       110
                ....*....|....*....|....*....|..
gi 125794    87 DLGIYFCSQTT------HVPPTFGGGTKLEIK 112
Cdd:cd20988  83 DEGSYYCASDTpgggreYDPLIFGKGTYLTVE 114

Immunoglobulin (Ig)-like domain of Programmed Cell Death 1 (PD1); The members here are composed of the immunoglobulin (Ig)-like domain of Programmed Cell Death 1 (PD1; also known as CD279/cluster of differentiation 279). PD1 is a cell surface receptor that is expressed on T cells and pro-B cells. The protein's structure includes an extracellular IgV domain followed by a transmembrane region and an intracellular tail. Activation of CD4+ T cells, CD8+ T cells, NKT cells, B cells, and monocytes induces PD-1 expression, immediately after which it binds two distinct ligands, PD-L1 (also known as B7-H1 or CD274/cluster of differentiation 274) and PD-L2, also known as B7-DC. PD-1 plays an important role in down regulating the immune system by preventing the activation of T-cells, reducing autoimmunity and promoting self-tolerance. The inhibitory effect of PD-1 is accomplished by promoting apoptosis in antigen specific T-cells in lymph nodes while simultaneously reducing apoptosis in regulatory T cells. A class of drugs that target PD-1, known as the PD-1 inhibitors, activate the immune system to attack tumors and treat cancer. Comparisons between the mouse PD-1 (mPD-1) and human PD-1 (hPD-1) reveals that unlike the mPD-1 which has a conventional IgSF V-set domain, hPD-1 lacks a C" strand, and instead the C' and D strands are connected by a long and flexible loop. In addition, the BC loop is not stabilized by disulfide bonding to the F strand of the ligand binding beta sheet. These differences result in different binding affinities of human and mouse PD-1 for their ligands.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794     5 TQTPLSLPVSLGDQASISCrssqSLVHSNGNTYLNWY-LQKAGQSPKLLIYKVSNRFSGVPDRFSGSG--SGTDFTLKIS 81
Cdd:cd16088   3 TFSPALLVVTEGANATFTC----SFSNTSESFVLNWYrLSPSNQTDKLAAFPEDRSQPGQDWRFRVTQlpNGRDFHMSVV 78

                        90
                ....*....|..
gi 125794    82 RVEAEDLGIYFC 93
Cdd:cd16088  79 RARRNDSGTYLC 90

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
                ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 125794    40 WYLQKAGQSPK---LLIYKVSNRFSGVPD----RFSGSGSGTDFTLKISRVEAEDLGIYFCS 94
Cdd:cd05720  32 WLFQPRGSAPQptfLLYLSSSNKTKWAEGldskRFSGSRSGSSYVLTLKDFRKEDEGYYFCS 93

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 125794       3 VMTQTPLSLPVSLGDQASISCRSSqslvhsngntylnwylqkAGQSPKLLIYKVSNRFSGVPDRFSGSGSGTdFTLKISR 82
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCEAT------------------GSPPPTITWYKNGEPISSGSTRSRSLSGSN-STLTISN 63

                          90
                  ....*....|.
gi 125794      83 VEAEDLGIYFC 93
Cdd:pfam13927  64 VTRSDAGTYTC 74

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 125794       6 QTPLSLPVSLGDQASISCRSSqslvHSNGNTYLNWylQKAGQSPKLLIYKVSNRfsgvpdrfsgsGSGTDFTLKISRVEA 85
Cdd:pfam00047   1 SAPPTVTVLEGDSATLTCSAS----TGSPGPDVTW--SKEGGTLIESLKVKHDN-----------GRTTQSSLLISNVTK 63

                          90
                  ....*....|....*..
gi 125794      86 EDLGIYFCSQTTHVPPT 102
Cdd:pfam00047  64 EDAGTYTCVVNNPGGSA 80