Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 49118589 131 APSVSIFPPSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHETY 210
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNKHKVY 80

                        90
                ....*....|....*....
gi 49118589 211 SCKVSHQG--KEIIQTLKR 227
Cdd:cd07699  81 TCEVTHEGlsSTITKSFNR 99

Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 49118589 131 APSVSIFPPSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHETY 210
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNKHKVY 80

                        90
                ....*....|....*....
gi 49118589 211 SCKVSHQG--KEIIQTLKR 227
Cdd:cd07699  81 TCEVTHEGlsSTITKSFNR 99

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|.
gi 49118589    148 KATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHETYSCKVSHQG 218
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNSDGTYFLSSYLTVPASTWESGDVYTCQVTHEG 71

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589     26 PASVSVSVGGTVTLTCQGNNIGGKYVHWYQQilpsAPRLIIYensqrpagiPERFSGTNSGNTASLTISGAQAEDEADYY 105
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYKQ----GGKLLAE---------SGRFSVSRSGSTSTLTISNVTPEDSGTYT 67

                           90
                   ....*....|....*....
gi 49118589    106 CQVWDSGAYIFgGGTQLTV 124
Cdd:smart00410  68 CAATNSSGSAS-SGTTLTV 85

Immunoglobulin light chain Constant domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) light chain constant (C) domain. 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 determine the type of immunoglobulin: 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 49118589 131 APSVSIFPPSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHETY 210
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNKHKVY 80

                        90
                ....*....|....*....
gi 49118589 211 SCKVSHQG--KEIIQTLKR 227
Cdd:cd07699  81 TCEVTHEGlsSTITKSFNR 99

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 49118589  23 LTQ-PASVSVSVGGTVTLTCQGNN-IGGKYVHWYQQILPSAPRLIIYENSQRPA---GIPERFSGT-NSGNTASLTISGA 96
Cdd:cd00099   1 VTQsPRSLSVQEGESVTLSCEVSSsFSSTYIYWYRQKPGQGPEFLIYLSSSKGKtkgGVPGRFSGSrDGTSSFSLTISNL 80

                        90       100       110
                ....*....|....*....|....*....|.
gi 49118589  97 QAEDEADYYCQVWDSGAY---IFGGGTQLTV 124
Cdd:cd00099  81 QPEDSGTYYCAVSESGGTdklTFGSGTRLTV 111

Immunoglobulin Constant-1 (C1)-set domain; The members here are composed of C1-set domains, classical Ig-like domains resembling the antibody constant domain. Members of the IgC1 family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, while the IgC domain is involved in oligomerization and molecular interactions. 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 strands by G, F, C, and C'.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 133 SVSIFPPSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHETYSC 212
Cdd:cd00098   1 TVTLLPPSPEEKGGGKVTLVCLVSGFYPKDITVTWLKNGVPLTSGVSTSSPVEPNDGTYSVTSSLTVPPSDWDEGATYTC 80

                        90
                ....*....|...
gi 49118589 213 KVSHQGKEIIQTL 225
Cdd:cd00098  81 VVTHESLKSPLSK 93

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 49118589    24 TQPASVSVSVGGTVTLTCQ---GNNIGGKYVHWYQQILPSAPR--LIIYENSQRPAGIPERFS--GTNSGNTASLTISGA 96
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTyssSMSEASTSVYWYRQPPGKGPTflIAYYSNGSEEGVKKGRFSgrGDPSNGDGSLTIQNL 80

                          90       100
                  ....*....|....*....|....*....
gi 49118589    97 QAEDEADYYCQVWDSGAYIFGGGTQLTVL 125
Cdd:pfam07686  81 TLSDSGTYTCAVIPSGEGVFGKGTRLTVL 109

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 49118589  24 TQ-PASVSVSVGGTVTLTCQGNNIGGKYVHWYQQILPSAPRLIIYENSQRPAGIPERFSGT-NSGNTAS-LTISGAQAED 100
Cdd:cd04983   2 TQsPQSLSVQEGENVTLNCNYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKGRFSATlDKSRKSSsLHISAAQLSD 81

                        90       100
                ....*....|....*....|....*..
gi 49118589 101 EADYYCQVWDSGAY---IFGGGTQLTV 124
Cdd:cd04983  82 SAVYFCALSESGGTgklTFGKGTRLTV 108

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin mu chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin constant domain (IgC) of mu heavy chains. This domain is found on the Fc fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEIA-TKKATVVCSLSDFTPRGATVKWLVDGKDQTDS--VQSSGLSKQSDNLYMESSYLSLTADQWLRHE 208
Cdd:cd16093   2 PTVSLHAPSREEFLgNRTATFVCLATGFSPKTISFKWLRNGKEVTSStgAVVEEPKEDGKTLYSATSFLTITESEWKSQT 81

                        90
                ....*....|
gi 49118589 209 TYSCKVSHQG 218
Cdd:cd16093  82 EFTCEFKHKG 91

CH3 domain (third constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, gamma, and delta chains, and CH4 domain (fourth constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, epsilon, and mu chains; member of the C1-set of I; The members here are composed of the third and fourth immunoglobulin constant domain (IgC) of alpha, delta, gamma and alpha, epsilon, and mu heavy chains, respectively. This domain is found on the Fc fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEIA-TKKATVVCSLSDFTPRGATVKWLVDGKD-QTDSVQSSGLSKQSDNLYMESSYLSLTADQWLRHET 209
Cdd:cd05768   1 PSVYLLPPPEEELSlNETVTLTCLVKGFYPEDIFVSWLQNGEPlPSADYKTTAPVPESDGSFFVYSKLNVSTADWNSGDV 80

                        90       100
                ....*....|....*....|..
gi 49118589 210 YSCKVSHQG--KEIIQ-TLKRS 228
Cdd:cd05768  81 FSCVVGHEAlpLQFTQkSIDKS 102

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 49118589  23 LTQ-PASVSVSVGGTVTLTCQgNNIGGKYVHWYQQILPSAPRLIIYENSQRPA---GIP-ERFSGT-NSGNTASLTISGA 96
Cdd:cd05899   1 VTQsPRYLIKRRGQSVTLRCS-QKSGHDNMYWYRQDPGKGLQLLFYSYGGGLNeegDLPgDRFSASrPSLTRSSLTIKSA 79

                        90       100       110
                ....*....|....*....|....*....|.
gi 49118589  97 QAEDEADYYCQV---WDSGAYIFGGGTQLTV 124
Cdd:cd05899  80 EPEDSAVYLCASslgGGADEAYFGPGTRLTV 110

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 49118589  25 QPASVSVSVGGTVTLTC--QGNNIGGKYVHWYQQILPSAPRLIIYENSQRPAGIPERFSGT--NSGNTASLTISGAQAED 100
Cdd:cd20988   4 EHQTVTVSVGKPVTLKCsmKGEAISNYYINWYRKTQGNTMTFIYREGGIYGPGFKDNFRGDidSSNNLAVLKILEASERD 83

                        90       100       110
                ....*....|....*....|....*....|
gi 49118589 101 EADYYCQVWDSGA------YIFGGGTQLTV 124
Cdd:cd20988  84 EGSYYCASDTPGGgreydpLIFGKGTYLTV 113

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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589  28 SVSVSVGGTVTLTCQGNNIGGKY-VHWYQQiLPSAP-RLIIYENSQRPAGIPERFSgTN---SGNTASLTISGAQAEDEA 102
Cdd:cd07706   8 DVSVQVGEEVTLNCRYETSWTNYyLFWYKQ-LPSGEmTFLIRQDSSEQNAKSGRYS-VNfqkAQKSISLTISALQLEDSA 85

                        90       100
                ....*....|....*....|....*
gi 49118589 103 DYYCQV---WDSGAYIFGGGTQLTV 124
Cdd:cd07706  86 KYFCALslpYDTDKLIFGKGTRLTV 110

CH3 domain (third constant Ig domain of heavy chains) in immunoglobulin heavy alpha, epsilon, and mu chains, and CH2 domain (second constant Ig domain of the gheavy chain) in immunoglobulin heavy gamma chain; member of the C1-set of Ig superfamily (IgSF) ; The members here are composed of the third immunoglobulin constant domain (IgC) of the gamma heavy chains and the second immunoglobulin constant domain (IgC) of alpha, epsilon, and mu heavy chains. This domain is found on the Fc fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEI-ATKKATVVCSLSDFTP-RGATVKWLVdgKDQTDSVQSSGLSKQSDN-LYMESSYLSLTADQWLRHE 208
Cdd:cd07696   1 VSVFLIPPSPKDLfLTKSAKVTCLVVDLTSiEEVNVTWSR--EDGNEVLASTTNPEKHYNaTLSVVSTLTVCADDWDNGK 78

                        90       100
                ....*....|....*....|
gi 49118589 209 TYSCKVSHQG--KEIIQTLK 226
Cdd:cd07696  79 TFKCKVTHPDlpSPIVKSIQ 98

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II beta chain. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes and they are also expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain has two globular domains (N- and C-terminal) and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEIAtKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADqwlRHETYS 211
Cdd:cd05766   4 PSVKVSPTKTGPLE-HPNLLVCSVTGFYPAEIEVKWFRNGQEETAGVVSTELIPNGDWTFQILVMLETTPR---RGDVYT 79

                ....*
gi 49118589 212 CKVSH 216
Cdd:cd05766  80 CQVEH 84

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and I-A; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of human histocompatibility antigen (HLA) DQ and mouse I-A. Three genetically distinct isotypes of class II MHC molecules are found in humans (HLA-DR, HLA-DQ, and HLA-DP), and two in mice (I-E and I-A). I-A and I-E have the same basic features insofar as peptide loading and presentation, they differ in that each interacts with distinctly different sets of peptides, and in the incidence of deletion of their genes. A structural understanding of the similarities and differences between I-A and I-E may help with understanding their roles in peptide presentation and T cell activation. Mouse I-Ag7 has a genetic susceptibility to autoimmune diabetes due to its small, uncharged amino acid residue at position 57 of their beta chain which results in the absence of a salt bridge between beta 57 and Arg alpha 76, which is adjacent to the P9 pocket of the peptide-binding groove. Human HLA-DR, -DQ, and -DP are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. HLA-DQ is involved in the autoimmune diseases celiac disease and diabetes mellitus type. DQ is one of several antigens involved in rejection of organ transplants. DQ2 is encoded by the HLA-DQB1*02 allele group. DQ6 is encoded by the HLA-DQB1*06 allele group. DQ2 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively. DQ6 beta-chains combine with alpha-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 alpha-chains. There are many haplotypes of DQ6. Susceptibility to Leptospirosis infection was found associated with undifferentiated DQ6. DQ8 is determined by the antibody recognition of beta8 and this generally detects the gene product of DQB1*0302. DQ8 is commonly linked to autoimmune disease in the human population. DQ8 is the second most predominant isoform linked to celiac disease and the DQ most linked to Type 1 diabetes. DQ8 increases the risk for rheumatoid arthritis and is linked to the primary risk locus for RA, HLA-DR4. DR4 also plays an important role in Type 1 diabetes. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune response. They are expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice, and induced in nonprofessional APCs, such as keratinocyctes; they are expressed on the surface of activated human T cells and on T cells from other species. MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes; these peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC, and bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 131 APSVSIFPpSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADqwlRHETY 210
Cdd:cd21001   3 EPTVTISP-SRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQ---RGDVY 78

                ....*.
gi 49118589 211 SCKVSH 216
Cdd:cd21001  79 TCHVEH 84

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and related proteins; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) DQ. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. Two autoimmune diseases in which HLA-DQ is involved are celiac disease and diabetes mellitus type 1. DQ is one of several antigens involved in rejection of organ transplants. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 130 KAPSVSIFPPSvEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSL--TADqwlrh 207
Cdd:cd21008   1 EVPEVTVFPKS-PVTLGQPNTLICLVDNIFPPVINITWLSNGHSVTEGVSETSFLSKSDHSFLKISYLTFlpSAD----- 74

                        90
                ....*....|.
gi 49118589 208 ETYSCKVSHQG 218
Cdd:cd21008  75 DIYDCKVEHWG 85

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 49118589  23 LTQPASVSVSVGGTVTLTCQ--GNNIGGKYVHWYQQilpsAP-------RLIIYENSQRPAGIP--ERFSGT--NSGNTA 89
Cdd:cd04981   2 LQESGPGLVKPGQSLKLSCKasGFTFTSYGMGWVRQ----APgkglewiGLIYPGGGDTYYADSfkGRFTITrdTSKSTA 77

                        90       100       110       120
                ....*....|....*....|....*....|....*....|
gi 49118589  90 SLTISGAQAEDEADYYC--QVWDSGAYIF---GGGTQLTV 124
Cdd:cd04981  78 YLQLNSLTSEDTAVYYCarGLGGYGYSYFdywGQGTTVTV 117

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin heavy alpha chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second immunoglobulin constant-1 set domain (IgC) of alpha heavy chains. This domain is found on the Fc fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEIAT-KKATVVCSLSDF-TPRGATVKWL-VDGKDqtdSVQSSGlSKQSDNLYMESSYLSLTADQWLRHE 208
Cdd:cd04986   2 PRLSLQRPALEDLLLgSNASLTCTLSGLkDPEGATFTWEpSGGKE---AIQGPP-ERDSCGCYSVSSVLPGCAEPWNSGD 77

                        90
                ....*....|....*.
gi 49118589 209 TYSCKVSHQGKEIIQT 224
Cdd:cd04986  78 TFSCTVTHPESKGTLT 93

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the first immunoglobulin constant-1 set domain of alpha chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, epsilon, gamma, and mu heavy chains. This domain is found on the Fab antigen-binding fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 133 SVSIFPPSVEEIATKKATVV-CSLSDFTPRGATVKWLVDGKDQTdsVQSSGLSKQSDNLYMESSYLSLTADQWLRHETYS 211
Cdd:cd21818   1 SPTVFPLSLCPSLSSDPVVIgCLVQGFFPEPVNVTWNYSGKGGT--ARNFPAMLASGGRYTQSSQLTLPADQCPEGEAYK 78

                ....*..
gi 49118589 212 CKVSHQG 218
Cdd:cd21818  79 CSVQHYS 85

T cell receptor (TCR) gamma chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) constant (C) 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 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.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 131 APSVSIFPPSVEEIATKKA-TVVCSLSDFTPRGATVKWLVDGKDqTDSVQSSGLSKQSDNLYMESSYLSLTADQwlRHET 209
Cdd:cd07697   1 SPKPTIFLPSIAETEKQKAgTYLCLLENFFPDVIKIHWREKKSD-TILESQEGNTEKTKDTYMKFSWLTVPKKS--LGKE 77

                ....*....
gi 49118589 210 YSCKVSHQG 218
Cdd:cd07697  78 HRCIYKHEN 86

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) DR; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) DR. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DR is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DRA1 and HLA-DRB1, that are adjacent to each other on chromosome band 6p21.31. Susceptibility to multiple sclerosis and rheumatoid arthritis are associated with the human histocompatibility leukocyte antigen HLA-DR2 and HLA-DR4, respectively. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPPSVEEIaTKKATVVCSLSDFTPRGATVKWLVDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQwlrHETYS 211
Cdd:cd21007   3 PEVTVLTNSPVEL-REPNVLICFIDKFTPPVVNVTWLRNGKPVTTGVSETVFLPREDHLFRKFHYLPFLPST---EDVYD 78

                ....*..
gi 49118589 212 CKVSHQG 218
Cdd:cd21007  79 CRVEHWG 85

Tapasin-R immunoglobulin-like domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin-like domain on Tapasin-R. Tapasin is a V-C1 (variable-constant) immunoglobulin superfamily molecule present in the endoplasmic reticulum (ER), where it links MHC class I molecules to the transporter associated with antigen processing (TAP). Tapasin-R is a tapasin-related protein that contains similar structural motifs to Tapasin, with some marked differences, especially in the V domain, transmembrane and cytoplasmic regions. The majority of Tapasin-R is located within the ER; however, there may be some expression of Tapasin-R at the cell surface. Tapasin-R lacks an obvious ER retention signal.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 132 PSVSIFPpSVEEIATKKATVVCSLSDFTPRGATVKWLVDGKDQT------DSVQSSGLSKQSDNLYMESSYLSLTADQWL 205
Cdd:cd05771   1 PRVRLSP-KNLVKPDLPQTLSCHIAGYYPLDVDVEWLREEPGGSesqvsrDGVSLSSHRQSVDGTYSISSYLTLEPGTEN 79

                        90
                ....*....|.
gi 49118589 206 RHETYSCKVSH 216
Cdd:cd05771  80 RGATYTCRVTH 90

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy epsilon and gamma chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the first immunoglobulin constant-1 set domain of epsilon and gamma chains. It belongs to a family composed of the first immunoglobulin constant-1 set domain of alpha, delta, epsilon, gamma, and mu heavy chains. This domain is found on the Fab antigen-binding fragment. 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 is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns. This group belongs to the C1-set of IgSF domains, which are classical Ig-like domains resembling the antibody constant domain. C1-set domains are found almost exclusively in molecules involved in the immune system, such as in immunoglobulin light and heavy chains, in the major histocompatibility complex (MHC) class I and II complex molecules, and in various T-cell receptors.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589 131 APSVSIFPPSVEEIATKKATVVCSLSDFTPRGATVKWlvDGKDQTDSVQSSGLSKQSDNLYMESSYLSLTADQWlRHETY 210
Cdd:cd21817   1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTW--NSGSLTSGVKTFPAVLQSSGLYTTSSQVTVPSSSW-GSQTF 77

                ....*.
gi 49118589 211 SCKVSH 216
Cdd:cd21817  78 TCNVEH 83

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 49118589  26 PASVSVSVGGTVTLTCQGNNI-GGKYVHWYQQIL-PSAPRLIIYENSQRPAG--------IPERFS--GTNSGNTASLTI 93
Cdd:cd07700   5 PGSLLVQTNQTVKMSCEAKTSpKNTRIYWLRQRQaPSKDSHFEFLASWDPSKgivygegvDQEKLIilSDSDSSRYILSL 84

                        90       100       110
                ....*....|....*....|....*....|.
gi 49118589  94 SGAQAEDEADYYCQVWDSGAYIFGGGTQLTV 124
Cdd:cd07700  85 MSVKPEDSGTYFCMTVGSPELIFGTGTKLSV 115

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 49118589  26 PASVSVSVGGTVTLTCQGNNIGGKYV-HWYqQILPS--APRLIIYENSQRPAGIPERFSGTNSGNTAS--LTISGAQAED 100
Cdd:cd16088   6 PALLVVTEGANATFTCSFSNTSESFVlNWY-RLSPSnqTDKLAAFPEDRSQPGQDWRFRVTQLPNGRDfhMSVVRARRND 84

                ....*.
gi 49118589 101 EADYYC 106
Cdd:cd16088  85 SGTYLC 90

Immunoglobulin (Ig)-like domain of protein zero (P0) and similar proteins; The members here are composed of the immunoglobulin (Ig) domain of protein zero (P0), a myelin membrane adhesion molecule. P0 accounts for over 50% of the total protein in peripheral nervous system (PNS) myelin. P0 is a single-pass transmembrane glycoprotein with a highly basic intracellular domain and an extracellular Ig domain. The extracellular domain of P0 (P0-ED) is similar to the Ig variable domain, carrying one acceptor sequence for N-linked glycosylation. P0 plays a role in membrane adhesion in the spiral wraps of the myelin sheath. The intracellular domain is thought to mediate membrane apposition of the cytoplasmic faces and may, through electrostatic interactions, interact directly with lipid headgroups. It is thought that homophilic interactions of the P0 extracellular domain mediate membrane juxtaposition in the extracellular space of PNS myelin. This group also contains the Ig domain of sodium channel subunit beta-2 (SCN2B), and of epithelial V-like antigen 1 (EVA). EVA, also known as myelin protein zero-like 2, is an adhesion molecule, which may play a role in structural organization of the thymus and early lymphocyte development. SCN2B subunits play a role in determining sodium channel density and function in neurons,and in control of electrical excitability in the brain.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589  21 IVLTQPASVSVSVGGTVTLTCQGNN---IGGKY-VHWYQQILPSAPRLII--YENSQRPAGIPERF------SGTNSGNT 88
Cdd:cd05715   1 MEVYTPRELNVLNGSDVRLTCTFTScytVGDAFsVTWTYQPEGGNTTESMfhYSKGKPYILKVGRFkdrvswAGNPSKKD 80

                        90       100
                ....*....|....*....|
gi 49118589  89 ASLTISGAQAEDEADYYCQV 108
Cdd:cd05715  81 ASIVISNLQFSDNGTYTCDV 100

Immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins. pIgR delivers dimeric IgA and pentameric IgM to mucosal secretions. Polymeric immunoglobulin (pIgs) are the first defense against pathogens and toxins. IgA and IgM can form polymers via an 18-residue extension at their C-termini referred to as the tailpiece. pIgR transports pIgs across mucosal epithelia into mucosal secretions. Human pIgR is a glycosylated type I transmembrane protein, comprised of a 620-residue extracellular region, a 23-residue transmembrane region, and a 103-residue cytoplasmic tail. The extracellular region contains five domains that share sequence similarity with Ig variable (v) regions. This group also contains the Ig-like extracellular domains of other receptors such as NK cell receptor Nkp44 and myeloid receptors, among others.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 49118589  23 LTQPASVSVSVGGTVTLTCQGNNIGGKYVHWYQQILPSAPRLIIyenSQRPAGIPERFSGTNSGN--TASLTISGAQAED 100
Cdd:cd05716   1 SVGPEVVTGVEGGSVTIQCPYPPKYASSRKYWCKWGSEGCQTLV---SSEGVVPGGRISLTDDPDngVFTVTLNQLRKED 77

                        90       100
                ....*....|....*....|....
gi 49118589 101 EADYYCQVWDSGAYifGGGTQLTV 124
Cdd:cd05716  78 AGWYWCGVGDDGDR--GLTVQVKL 99