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 10799664   5 GPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNFGTQTYTCN 84
Cdd:cd21817   1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTWNSGSLTSGVKTFPAVLQSSGLYTTSSQVTVPSSSWGSQTFTCN 80

                        90
                ....*....|....
gi 10799664  85 VDHKPSNTKVDKTV 98
Cdd:cd21817  81 VEHKPSSTKVDKKI 94

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 10799664 118 SVFLFPPKPKDTLMiSRTPEVTCVVVDVShEDPEVQFNWYV-DGMEVHnAKTKPREEQFNSTFRVVSVLTVVHQDWLNGK 196
Cdd:cd07696   2 SVFLIPPSPKDLFL-TKSAKVTCLVVDLT-SIEEVNVTWSReDGNEVL-ASTTNPEKHYNATLSVVSTLTVCADDWDNGK 78

                        90       100
                ....*....|....*....|
gi 10799664 197 EYKCKVSNKGLPAPIEKTIS 216
Cdd:cd07696  79 TFKCKVTHPDLPSPIVKSIQ 98

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 10799664   5 GPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNFGTQTYTCN 84
Cdd:cd21817   1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTWNSGSLTSGVKTFPAVLQSSGLYTTSSQVTVPSSSWGSQTFTCN 80

                        90
                ....*....|....
gi 10799664  85 VDHKPSNTKVDKTV 98
Cdd:cd21817  81 VEHKPSSTKVDKKI 94

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 10799664 118 SVFLFPPKPKDTLMiSRTPEVTCVVVDVShEDPEVQFNWYV-DGMEVHnAKTKPREEQFNSTFRVVSVLTVVHQDWLNGK 196
Cdd:cd07696   2 SVFLIPPSPKDLFL-TKSAKVTCLVVDLT-SIEEVNVTWSReDGNEVL-ASTTNPEKHYNATLSVVSTLTVCADDWDNGK 78

                        90       100
                ....*....|....*....|
gi 10799664 197 EYKCKVSNKGLPAPIEKTIS 216
Cdd:cd07696  79 TFKCKVTHPDLPSPIVKSIQ 98

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 10799664    241 QVSLTCLVKGFYPSDIAVEWESNGQP-ENNYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNH 314
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEvTEGVSTTDPLKNSDGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664     8 VFPLAPCSRSTSEsTAALGCLVKDYFPEPVTVSW--NSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNF-GTQTYTCN 84
Cdd:pfam07654   1 VYVFPPSPEELGK-PNTLTCLVTGFYPPDITVTWlkNGQEVTEGVKTTPPSPNSDWTYQLSSYLTVTPSDWeSGDEYTCR 79

                  ....
gi 10799664    85 VDHK 88
Cdd:pfam07654  80 VEHE 83

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 10799664    138 VTCVVVDVSHEDPEVQfnWYVDGMEVH-NAKTKPREEQFNSTFRVVSVLTVVHQDWLNGKEYKCKVSNKGLPAP 210
Cdd:smart00407   4 LVCLVSGFYPPDITVT--WLRNGQEVTeGVSTTDPLKNSDGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

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 10799664   5 GPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNFGTQTYTCN 84
Cdd:cd21817   1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTWNSGSLTSGVKTFPAVLQSSGLYTTSSQVTVPSSSWGSQTFTCN 80

                        90
                ....*....|....
gi 10799664  85 VDHKPSNTKVDKTV 98
Cdd:cd21817  81 VEHKPSSTKVDKKI 94

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 10799664 118 SVFLFPPKPKDTLMiSRTPEVTCVVVDVShEDPEVQFNWYV-DGMEVHnAKTKPREEQFNSTFRVVSVLTVVHQDWLNGK 196
Cdd:cd07696   2 SVFLIPPSPKDLFL-TKSAKVTCLVVDLT-SIEEVNVTWSReDGNEVL-ASTTNPEKHYNATLSVVSTLTVCADDWDNGK 78

                        90       100
                ....*....|....*....|
gi 10799664 197 EYKCKVSNKGLPAPIEKTIS 216
Cdd:cd07696  79 TFKCKVTHPDLPSPIVKSIQ 98

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, delta, epsilon, gamma, and mu chains; 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, 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 10799664   5 GPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSW---NSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNFGT-QT 80
Cdd:cd04985   1 APTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWqknTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSgEV 80

                        90
                ....*....|....*...
gi 10799664  81 YTCNVDHKPSNTKVDKTV 98
Cdd:cd04985  81 YKCQVQHSASNSKQEKDV 98

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 10799664 226 QVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPEN-NYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGNVFSC 304
Cdd:cd00098   1 TVTLLPPSPEEKGGGKVTLVCLVSGFYPKDITVTWLKNGVPLTsGVSTSSPVEPNDGTYSVTSSLTVPPSDWDEGATYTC 80

                ....*..
gi 10799664 305 SVMHEAL 311
Cdd:cd00098  81 VVTHESL 87

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy mu 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 mu 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 10799664   6 PSVFPLAPCSRSTSeSTAALGCLVKDYFPEPVTVSWNSG--ALTSGVHTFPAVLqSSGLYSLSSVVTVTSSNFGTQT-YT 82
Cdd:cd21819   2 PTLFPLVSCGSSTS-DPVTVGCLATDFLPDSITFSWTDDnnSLTTGVKTYPSVL-TGGTYTASSQLQVPESEWKSKEnFY 79

                        90
                ....*....|...
gi 10799664  83 CNVDHKPSNTKVD 95
Cdd:cd21819  80 CKVEHPGGNKEVP 92

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 10799664   6 PSVFPLAPCSRSTSESTAaLGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSN-FGTQTYTCN 84
Cdd:cd21818   2 PTVFPLSLCPSLSSDPVV-IGCLVQGFFPEPVNVTWNYSGKGGTARNFPAMLASGGRYTQSSQLTLPADQcPEGEAYKCS 80

                        90
                ....*....|....
gi 10799664  85 VDHkpSNTKVDKTV 98
Cdd:cd21818  81 VQH--YSPSQDLNV 92

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 10799664 224 EPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQP-ENNYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGNVF 302
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTvSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNKHKVY 80

                ....*....
gi 10799664 303 SCSVMHEAL 311
Cdd:cd07699  81 TCEVTHEGL 89

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 10799664 225 PQVYTLPPSREEMTKNQ-VSLTCLVKGFYPSDIAVEWESNG---QPENNYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGN 300
Cdd:cd16093   2 PTVSLHAPSREEFLGNRtATFVCLATGFSPKTISFKWLRNGkevTSSTGAVVEEPKEDGKTLYSATSFLTITESEWKSQT 81

                        90       100
                ....*....|....*....|.
gi 10799664 301 VFSCSVMHEalhNHYTQKSLS 321
Cdd:cd16093  82 EFTCEFKHK---GEIVEKNAS 99

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 10799664 118 SVFLFPPKPKDTLmiSRTPEVTCVVVDVSHEDpeVQFNWYVDGMEVHNAKTKPRE-EQFNSTFRVVSVLTVVHQDWLNGK 196
Cdd:cd00098   1 TVTLLPPSPEEKG--GGKVTLVCLVSGFYPKD--ITVTWLKNGVPLTSGVSTSSPvEPNDGTYSVTSSLTVPPSDWDEGA 76

                        90
                ....*....|....*....
gi 10799664 197 EYKCKVSNKGLPAPIEKTI 215
Cdd:cd00098  77 TYTCVVTHESLKSPLSKTW 95

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 10799664   6 PSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSW--NSGALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNFGT-QTYT 82
Cdd:cd07699   2 PSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWkvDGSTVSSGVTTSKTEQQSDNTYSMSSYLTLSSSDWNKhKVYT 81

                        90
                ....*....|....*...
gi 10799664  83 CNVDHKPSNTKVDKTVER 100
Cdd:cd07699  82 CEVTHEGLSSTITKSFNR 99

CH1 domain (first constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, delta, epsilon, gamma, and mu chains; 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, 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 10799664 225 PQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEW--ESNGQPENNYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGNVF 302
Cdd:cd04985   2 PTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWqkNTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSGEVY 81

                ....*...
gi 10799664 303 SCSVMHEA 310
Cdd:cd04985  82 KCQVQHSA 89

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 10799664   6 PSVFPLAPCSRS-TSESTAALGCLVKDYFPEPVTVSWNSG---ALTSGVHTFPAVLQSSGLYSLSSVVTVTSSNF-GTQT 80
Cdd:cd05768   1 PSVYLLPPPEEElSLNETVTLTCLVKGFYPEDIFVSWLQNgepLPSADYKTTAPVPESDGSFFVYSKLNVSTADWnSGDV 80

                        90       100
                ....*....|....*....|..
gi 10799664  81 YTCNVDHKP-SNTKVDKTVERK 101
Cdd:cd05768  81 FSCVVGHEAlPLQFTQKSIDKS 102

Immunoglobulin domain of Cluster of Differentiation (CD) 1; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Cluster of Differentiation (CD) 1. CD1 family of transmembrane glycoproteins, are structurally related to the major histocompatibility complex (MHC) proteins and form heterodimers with beta-2-microglobulin. They mediate the presentation of primarily lipid and glycolipid antigens of self or microbial origin to T cells. The human genome contains five CD1 family genes (CD1a, CD1b, CD1c, CD1d, and CD1e) organized in a cluster on chromosome 1. The CD1 family members are thought to differ in their cellular localization and specificity for particular lipid ligands. CD1a localizes to the plasma membrane and to recycling vesicles of the early endocytic system. Alternative splicing results in multiple transcript variants. Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I alpha chain. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells. C1-set Ig domains 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 10799664 233 SREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPML-DSDGSFFLYSKLTVDKsrwQQGNVFSCSVMHEAL 311
Cdd:cd21029   9 SRPSPGDGHLQLSCHVTGFYPRPIEVTWLRDGQEQMDGTQSGGILpNHDGTYQLRKTLDIAP---GEGAGYSCRVDHSSL 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 10799664 225 PQVyTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEW--ESNGQPE-----NNYKTTPPMLDSDGSFFLYSKLTVDKSRWQ 297
Cdd:cd05771   1 PRV-RLSPKNLVKPDLPQTLSCHIAGYYPLDVDVEWlrEEPGGSEsqvsrDGVSLSSHRQSVDGTYSISSYLTLEPGTEN 79

                        90
                ....*....|....
gi 10799664 298 QGNVFSCSVMHEAL 311
Cdd:cd05771  80 RGATYTCRVTHVSL 93

Class I major histocompatibility complex (MHC) beta-2-microglobulin; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin-like domain in beta-2-microglobulin (beta2m). Beta2m is the non-covalently bound light chain of the human class I major histocompatibility complex (MHC-I). Beta2m is structured as a beta-sandwich domain composed of two facing beta-sheets (four stranded and three stranded), that is typical of the C-type immunoglobulin superfamily. This structure is stabilized by an intramolecular disulfide bridge connecting two Cys residues in the facing beta-sheets. In vivo, MHC-I continuously exposes beta2m on the cell surface, where it may be released to plasmatic fluids, transported to the kidneys, degraded, and finally excreted.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664 226 QVYTLPPSrEEMTKNQvsLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPMLDSDGSFFL--YSKLTVDKsrwqqGNVFS 303
Cdd:cd05770   6 QVYSRFPA-ENGKPNV--LNCYVSGFHPPDIEIRLLKNGVKIEDVEQSDLSFSKDWTFYLlkYTEFTPTK-----GDEYA 77

                ....*...
gi 10799664 304 CSVMHEAL 311
Cdd:cd05770  78 CRVRHNTL 85

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 10799664 224 EPQVyTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPEN-NYKTTPPMLDSDGSFFLYSKLTVDKsrwQQGNVF 302
Cdd:cd21001   3 EPTV-TISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETaGVVSTPLIRNGDWTFQILVMLEMTP---QRGDVY 78

                ....*....
gi 10799664 303 SCSVMHEAL 311
Cdd:cd21001  79 TCHVEHPSL 87

Class I major histocompatibility complex (MHC) alpha chain, alpha3 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 I alpha chain. Class I MHC proteins bind antigenic peptide fragments and present them to CD8+ T lymphocytes. Class I molecules consist of a transmembrane alpha chain and a small chain called the beta-2-microglobulin. The alpha chain contains three extracellular domains, two of which fold together to form the peptide-binding cleft (alpha1 and alpha2), and one which has an Ig fold (alpha3). Peptide binding to class I molecules occurs in the endoplasmic reticulum (ER) and involves both chaperones and dedicated factors to assist in peptide loading. Class I MHC molecules are expressed on most nucleated cells.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664 231 PPS----REEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPEnnyktTPPML------DSDGSFFLYSKLTVDKSRWQqgn 300
Cdd:cd07698   2 PPKvhvtHHPRSDGESTLRCWALGFYPAEITLTWQRDGEDQ-----TQDMElvetrpNGDGTFQKWAAVVVPSGEEQ--- 73

                        90
                ....*....|....*.
gi 10799664 301 VFSCSVMHEALHNHYT 316
Cdd:cd07698  74 RYTCHVQHEGLPEPLT 89

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 10799664   6 PSVFPLAPcSRS--TSESTAALGCLVKDYFPEPVTVSW--NSGALTS--GVHTFPAVLQSSGLYSLSSVVTVTSSNFGTQ 79
Cdd:cd16093   2 PTVSLHAP-SREefLGNRTATFVCLATGFSPKTISFKWlrNGKEVTSstGAVVEEPKEDGKTLYSATSFLTITESEWKSQ 80

                        90       100
                ....*....|....*....|.
gi 10799664  80 T-YTCNVDHKpsNTKVDKTVE 99
Cdd:cd16093  81 TeFTCEFKHK--GEIVEKNAS 99

T cell receptor (TCR) beta chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the T cell receptor (TCR) beta chain constant immunoglobulin domain. 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 beta chain. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The antigen binding site is formed by the variable domains of the alpha and beta chains, located at the N-terminus of each chain. Alpha/beta TCRs recognize antigens differently from gamma/delta TCRs.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664   4 KGPSVFPLAPCSRSTSEST-AALGCLVKDYFPEPVTVSW--NSGALTSGVHTFPAVLQSSG-LYSLSS--VVTVTSSNFG 77
Cdd:cd05769   1 TPPTVALFPPSEAEIRNKRkATLVCLATGFYPDHVSLSWkvNGKEVKDGVATDPQALRENTsTYSLSSrlRVSATEWFNP 80

                        90
                ....*....|....*....
gi 10799664  78 TQTYTCNVDHKPsNTKVDK 96
Cdd:cd05769  81 RNTFTCIVKFYG-GTDTDT 98

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP; 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 histocompatibility antigen (HLA) DP. HLA class II histocompatibility antigen, DP(W2) beta chain is a protein that in humans is encoded by the HLA-DPB1 gene. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DP is an alphabeta heterodimer cell-surface receptor. Each DP subunit (alpha-subunit, beta-subunit) is composed of a alpha-helical N-terminal domain, an IgG-like beta sheet, a membrane spanning domain, and a cytoplasmic domain. The alpha-helical domain forms the sides of the peptide binding groove. The beta sheet regions form the base of the binding groove and the bulk of the molecule as well as the inter-subunit (non-covalent) binding region. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. 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 10799664 224 EPQVYtLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPEN-NYKTTPPMLDSDGSFFLYSKLTVDKsrwQQGNVF 302
Cdd:cd21003   3 QPKVN-VSPSKKGPLQHHNLLVCHVTDFYPGNIQVRWFLNGQEETaGVVSTNLIHNGDWTFQILVMLEMTP---QQGDVY 78

                ....*....
gi 10799664 303 SCSVMHEAL 311
Cdd:cd21003  79 TCQVEHPSL 87

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin E (IgE); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the second constant domain of the heavy chain of immunoglobulin E (IgE). The basic structure of immunoglobulin (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). The different classes of antibodies vary in their heavy chains; the IgE class has the epsilon type. This domain (Cepsilon2) of IgE is in place of the flexible hinge region found in IgG.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664   6 PSVFPLAP-CSRSTSESTAALGCLVKDYFPEPVTVSW---NSGALTSGVHTFPAVlQSSGLYSLSSVVTVTSSNFGTQ-T 80
Cdd:cd05847   1 PTVQILHSsCASTLTSETIQLLCLISGYTPSTIEVEWlvdGQVATLSAASTAPQK-EEGGTFSTTSKLNVTQEDWKSGkT 79

                ....*..
gi 10799664  81 YTCNVDH 87
Cdd:cd05847  80 YTCKVTH 86

CH2 domain (second constant Ig domain of the heavy chain) in immunoglobulin delta chain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin constant domain (IgC) in delta heavy chains. The IgC family includes 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, and the IgC domain is involved in oligomerization and molecular interactions.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664 227 VYTLPPSREEM-TKNQVSLTCLVKGFYPSDIAVEWESNGQ-PENNYKTTPPMLDSDGSFFLYSKLTVDKSRWQQGNVFSC 304
Cdd:cd16084   2 VYLLTPAVQDLwLRDKATFTCFVVGSDLKDAHLTWEVAGKvPTGGVEEGLLERHSNGSQSQHSRLTLPRSLWNAGTSVTC 81

                ....*..
gi 10799664 305 SVMHEAL 311
Cdd:cd16084  82 TLNHPSL 88

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-1b; member of the C1-set of Ig superfamily (IgSF) domains; The non-classical mouse MHC class I (MHC-I) molecule Qa-1b is a non-polymorphic MHC molecule with an important function in innate immunity. It binds and presents signal peptides of classical MHC-I molecules at the cell surface and, as such, act as an indirect sensor for the normal expression of MHC-I molecules. This signal peptide dominantly accommodated in the groove of Qa-1b is called Qdm, for Qa-1 determinant modifier, and its amino acid sequence AMAPRTLLL is highly conserved among mammalian species. The Qdm/Qa-1b complex serves as a ligand for the germ-line encoded heterodimeric CD94/NKG2A receptors expressed on natural killer (NK) cells and activated CD8+ T cells and transduces inhibitory signals to these lymphocytes. Thus, upon binding, Qa-1b signals NK cells not to engage in cell lysis. The molecular basis of Qa-1b function is unclear.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10799664 219 KGQPREPQVYTLPPSREEMTknqvsLTCLVKGFYPSDIAVEWESNG----QPENNYKTTPPmldSDGSFFLYSKLTVDKS 294
Cdd:cd21820   2 RSDPPKAHVTHHPRSEDEVT-----LRCWALGFYPADITLTWQLNGeeltQDMELVETRPA---GDGTFQKWAAVVVPLG 73

                        90
                ....*....|....*..
gi 10799664 295 RWQqgnVFSCSVMHEAL 311
Cdd:cd21820  74 KEQ---YYTCHVYHEGL 87