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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        5 VTQTGGQVALSEEDFLTIHCNYSASGYPALFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATYNKEATSFHLQKASVQES 84
Cdd:cd04983   1 VTQSPQSLSVQEGENVTLNCNYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKGRFSATLDKSRKSSSLHISAAQLS 80

                        90       100
                ....*....|....*....|....*...
2PXY_A       85 DSAVYYCALSENYGNEKITFGAGTKLQV 112
Cdd:cd04983  81 DSAVYFCALSESGGTGKLTFGKGTRLTV 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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        5 VTQTGGQVALSEEDFLTIHCNYSASGYPALFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATYNKEATSFHLQKASVQES 84
Cdd:cd04983   1 VTQSPQSLSVQEGENVTLNCNYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKGRFSATLDKSRKSSSLHISAAQLS 80

                        90       100
                ....*....|....*....|....*...
2PXY_A       85 DSAVYYCALSENYGNEKITFGAGTKLQV 112
Cdd:cd04983  81 DSAVYFCALSESGGTGKLTFGKGTRLTV 108

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A          20 LTIHCNYSASGYPALFWYVQypgeGPQFLFRASRdkekgssrgFEATYNKeaTSFHLQKASVQESDSAVYYCALSENYGN 99
Cdd:smart00410  12 VTLSCEASGSPPPEVTWYKQ----GGKLLAESGR---------FSVSRSG--STSTLTISNVTPEDSGTYTCAATNSSGS 76

                           90
                   ....*....|...
2PXY_A         100 EKitfgAGTKLQV 112
Cdd:smart00410  77 AS----SGTTLTV 85

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        5 VTQTGGQVALSEEDFLTIHCNYSASGYPALFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATYNKEATSFHLQKASVQES 84
Cdd:cd04983   1 VTQSPQSLSVQEGENVTLNCNYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKGRFSATLDKSRKSSSLHISAAQLS 80

                        90       100
                ....*....|....*....|....*...
2PXY_A       85 DSAVYYCALSENYGNEKITFGAGTKLQV 112
Cdd:cd04983  81 DSAVYFCALSESGGTGKLTFGKGTRLTV 108

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) delta chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the delta 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 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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        5 VTQTGGQVALSEEDFLTIHCNYSAS-GYPALFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATYNKEATSFHLQKASVQE 83
Cdd:cd07706   2 VTQAQPDVSVQVGEEVTLNCRYETSwTNYYLFWYKQLPSGEMTFLIRQDSSEQNAKSGRYSVNFQKAQKSISLTISALQL 81

                        90       100       110
                ....*....|....*....|....*....|.
2PXY_A       84 SDSAVYYCALSENYGNEKITFGAGTKLQVVP 114
Cdd:cd07706  82 EDSAKYFCALSLPYDTDKLIFGKGTRLTVEP 112

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        5 VTQTGGQVALSEEDFLTIHCNYSAS-GYPALFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATYNkeATSFHLQKASVQE 83
Cdd:cd04980   3 MTQSPASLSVSPGERVTISCKASQSiSSNYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGS--GTDFTLTISSVEP 80

                        90       100
                ....*....|....*....|....*....
2PXY_A       84 SDSAVYYCalsENYGNEKITFGAGTKLQV 112
Cdd:cd04980  81 EDAAVYYC---QQGYTFPYTFGGGTKLEI 106

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
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A         20 LTIHCNYSAS---GYPALFWYVQYPGEGPQFLF-RASRDKEKGSSRG-FEATYNKEATSFHLQKASVQESDSAVYYCALs 94
Cdd:pfam07686  14 VTLPCTYSSSmseASTSVYWYRQPPGKGPTFLIaYYSNGSEEGVKKGrFSGRGDPSNGDGSLTIQNLTLSDSGTYTCAV- 92

                          90
                  ....*....|....*....
2PXY_A         95 enYGNEKITFGAGTKLQVV 113
Cdd:pfam07686  93 --IPSGEGVFGKGTRLTVL 109

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A        6 TQTGGQVALSEEdfltihcnysASGYPA---LFWY--VQYPGEGPQFLFRASRDKEKGSSRGFEATYNKE-------ATS 73
Cdd:cd07700  10 VQTNQTVKMSCE----------AKTSPKntrIYWLrqRQAPSKDSHFEFLASWDPSKGIVYGEGVDQEKLiilsdsdSSR 79

                        90       100       110       120
                ....*....|....*....|....*....|....*....|
2PXY_A       74 FHLQKASVQESDSAVYYCALsenYGNEKITFGAGTKLQVV 113
Cdd:cd07700  80 YILSLMSVKPEDSGTYFCMT---VGSPELIFGTGTKLSVV 116

Immunoglobulin (Ig) lambda light chain variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, lambda type, variable (V) domain. 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. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A       21 TIHCNYSASGYPA--LFWYVQYPGEGPQFLFRASRDKEKGSSRGFEATynKEATSFHLQKASVQESDSAVYYCALSenYG 98
Cdd:cd04984  17 TITCTGSSGNISGnyVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGS--KSGNTASLTISGAQTEDEADYYCQVW--DS 92

                        90
                ....*....|....
2PXY_A       99 NEKItFGAGTKLQV 112
Cdd:cd04984  93 NSYV-FGGGTKLTV 105

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A       34 LFWYVQYPGEGPQFLfrASRDKEKGSSRGFEATYNKEATS--FHLQKASVQESDSAVYYCALSENYGN--EKITFGAGTK 109
Cdd:cd16095  34 LSWYLWVPGHAPLWL--TSLDHISTKVSEDRITSSREDTNsqIFLQIKGLGLRDSGQYHCARRVGYGDdtDKLIFGPGTD 111

                ...
2PXY_A      110 LQV 112
Cdd:cd16095 112 VIV 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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
2PXY_A       11 QVALSEEDFLTIHCNYS-ASGYPALFWYVQYPGEGPQFLFRASRDK-EKGSSRGFEATYNKEATSFHLQKASVQESDSAV 88
Cdd:cd16088   8 LLVVTEGANATFTCSFSnTSESFVLNWYRLSPSNQTDKLAAFPEDRsQPGQDWRFRVTQLPNGRDFHMSVVRARRNDSGT 87

                ....
2PXY_A       89 YYCA 92
Cdd:cd16088  88 YLCG 91