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 52695903 112 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKV 191
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                        90       100
                ....*....|....*....|
gi 52695903 192 YACEVTHQGLSSPVTKSFNR 211
Cdd:cd07699  80 YTCEVTHEGLSSTITKSFNR 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 52695903 112 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKV 191
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                        90       100
                ....*....|....*....|
gi 52695903 192 YACEVTHQGLSSPVTKSFNR 211
Cdd:cd07699  80 YTCEVTHEGLSSTITKSFNR 99

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 52695903    129 TASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSP 204
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNS-DGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

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 52695903     6 QSPSSLSASVGDRVTITCRASQSYAYA---VAWYQQKPGKAPKLLIYDASYLY--SGVPSRFSGSG--SGTDFTLTISSL 78
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSSSMSEAstsVYWYRQPPGKGPTFLIAYYSNGSeeGVKKGRFSGRGdpSNGDGSLTIQNL 80

                          90       100
                  ....*....|....*....|....*...
gi 52695903    79 QPEDFATYYCQQAYSSPDTFGQGTKVEI 106
Cdd:pfam07686  81 TLSDSGTYTCAVIPSGEGVFGKGTRLTV 108

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 52695903 112 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKV 191
Cdd:cd07699   1 APSVTIFPPSSEELSSGKATLVCLINKFYPGFATVTWKVDGSTVSSGVTTSKTEQQS-DNTYSMSSYLTLSSSDWNKHKV 79

                        90       100
                ....*....|....*....|
gi 52695903 192 YACEVTHQGLSSPVTKSFNR 211
Cdd:cd07699  80 YTCEVTHEGLSSTITKSFNR 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 52695903   4 MTQSPSSLSASVGDRVTITCRASQSYA-YAVAWYQQKPGKAPKLLIYDASYLYS---GVPSRFSGSGSG-TDFTLTISSL 78
Cdd:cd00099   1 VTQSPRSLSVQEGESVTLSCEVSSSFSsTYIYWYRQKPGQGPEFLIYLSSSKGKtkgGVPGRFSGSRDGtSSFSLTISNL 80

                        90       100       110
                ....*....|....*....|....*....|.
gi 52695903  79 QPEDFATYYCQQAYSS---PDTFGQGTKVEI 106
Cdd:cd00099  81 QPEDSGTYYCAVSESGgtdKLTFGSGTRLTV 111

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 52695903   115 VFIFPPSDEQLKsGTASVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC 194
Cdd:pfam07654   1 VYVFPPSPEELG-KPNTLTCLVTGFYPPDITVTWLKNGQEVT-EGVKTTPPSPNSDWTYQLSSYLTVTPSDWESGDEYTC 78

                  ....*..
gi 52695903   195 EVTHQGL 201
Cdd:pfam07654  79 RVEHEGL 85

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 52695903 113 PSVFIFPPSDEQL-KSGTASVVCLLNNFYPREAKVQWKVDN-ALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHK 190
Cdd:cd05768   1 PSVYLLPPPEEELsLNETVTLTCLVKGFYPEDIFVSWLQNGePLPSADYKTTAPVPES-DGSFFVYSKLNVSTADWNSGD 79

                        90       100
                ....*....|....*....|..
gi 52695903 191 VYACEVTHQGLSSPVT-KSFNR 211
Cdd:cd05768  80 VFSCVVGHEALPLQFTqKSIDK 101

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 52695903   5 TQSPSSLSASVGDRVTITCRASQSYaYAVAWYQQKPGKAPKLLIYDAS---YLYSGVP-SRFSGSG-SGTDFTLTISSLQ 79
Cdd:cd05899   2 TQSPRYLIKRRGQSVTLRCSQKSGH-DNMYWYRQDPGKGLQLLFYSYGgglNEEGDLPgDRFSASRpSLTRSSLTIKSAE 80

                        90       100
                ....*....|....*....|....*....
gi 52695903  80 PEDFATYYCqqAYSSPDT-----FGQGTK 103
Cdd:cd05899  81 PEDSAVYLC--ASSLGGGadeayFGPGTR 107

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 52695903      8 PSSLSASVGDRVTITCRASQSYAYAVAWYQQKPgkapKLLIYdasylysgvPSRFSGSGSGTDFTLTISSLQPEDFATYY 87
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYKQGG----KLLAE---------SGRFSVSRSGSTSTLTISNVTPEDSGTYT 67

                           90
                   ....*....|....*....
gi 52695903     88 CQQAYSSPDTFGqGTKVEI 106
Cdd:smart00410  68 CAATNSSGSASS-GTTLTV 85

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 52695903 112 APSVFIFPPS-DEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQ-ESVTEQDSkDSTYSLSSTLTLSKADYEK- 188
Cdd:cd05769   2 PPTVALFPPSeAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVAtDPQALREN-TSTYSLSSRLRVSATEWFNp 80

                        90       100
                ....*....|....*....|....*
gi 52695903 189 HKVYACEVTHQGLSSpvTKSFNRGE 213
Cdd:cd05769  81 RNTFTCIVKFYGGTD--TDTWTQGI 103

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 52695903 113 PSVFIFPPS-DEQLKSGTASVVCLLNNFYPREAKVQW-KVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHK 190
Cdd:cd16093   2 PTVSLHAPSrEEFLGNRTATFVCLATGFSPKTISFKWlRNGKEVTSSTGAVVEEPKEDGKTLYSATSFLTITESEWKSQT 81

                        90
                ....*....|.
gi 52695903 191 VYACEVTHQGL 201
Cdd:cd16093  82 EFTCEFKHKGE 92

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 52695903 113 PSVFIFPPSDEQL-KSGTASVVCLLNNFYPREA-KVQWKVdnalQSGNSQESVTEQDSK--DSTYSLSSTLTLSKADYEK 188
Cdd:cd07696   1 VSVFLIPPSPKDLfLTKSAKVTCLVVDLTSIEEvNVTWSR----EDGNEVLASTTNPEKhyNATLSVVSTLTVCADDWDN 76

                        90       100
                ....*....|....*....|
gi 52695903 189 HKVYACEVTHQGLSSPVTKS 208
Cdd:cd07696  77 GKTFKCKVTHPDLPSPIVKS 96

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 52695903 112 APSVFIFPPSD-EQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDsKDsTYSLSSTLTLSKADYEkhK 190
Cdd:cd07697   1 SPKPTIFLPSIaETEKQKAGTYLCLLENFFPDVIKIHWREKKSDTILESQEGNTEKT-KD-TYMKFSWLTVPKKSLG--K 76

                        90
                ....*....|....*...
gi 52695903 191 VYACEVTHQGLSSPVTKS 208
Cdd:cd07697  77 EHRCIYKHENNKNGVKQE 94

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 52695903 112 APSVFIF---PPSDEQLKsgtasVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADyeK 188
Cdd:cd21029   2 KPRVRLSsrpSPGDGHLQ-----LSCHVTGFYPRPIEVTWLRDGQEQM-DGTQSGGILPNHDGTYQLRKTLDIAPGE--G 73

                        90
                ....*....|....*...
gi 52695903 189 HKvYACEVTHQGLSSPVT 206
Cdd:cd21029  74 AG-YSCRVDHSSLKQDLI 90

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 52695903 112 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKV 191
Cdd:cd04985   1 APTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWQKNTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSGEV 80

                        90
                ....*....|....*.
gi 52695903 192 YACEVTHQGLSSPVTK 207
Cdd:cd04985  81 YKCQVQHSASNSKQEK 96

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 52695903 113 PSVFIFPPSdEQLKSGTASVVCLLNNFYPREAKVQW----KVDNALQSGNSQESV-TEQDSKDSTYSLSSTLTLSKADYE 187
Cdd:cd05771   1 PRVRLSPKN-LVKPDLPQTLSCHIAGYYPLDVDVEWlreePGGSESQVSRDGVSLsSHRQSVDGTYSISSYLTLEPGTEN 79

                        90       100
                ....*....|....*....|.
gi 52695903 188 KHKVYACEVTHQGLSSPVTKS 208
Cdd:cd05771  80 RGATYTCRVTHVSLEEPLSVS 100

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 52695903 111 AAPSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnalqSGNSQESVTEQDSK------DSTYSLSSTL--TLS 182
Cdd:cd21001   2 VEPTVTISPSRTEALNHHNL-LVCSVTDFYPGQIKVRW-------FRNDQEETAGVVSTplirngDWTFQILVMLemTPQ 73

                        90       100
                ....*....|....*....|....
gi 52695903 183 KADyekhkVYACEVTHQGLSSPVT 206
Cdd:cd21001  74 RGD-----VYTCHVEHPSLQSPIT 92

Immunoglobulin (Ig) variable (V) domain of Cluster of Differentiation (CD) 8 beta chain; The members here are composed of the immunoglobulin (Ig)-like domain in Cluster of Differentiation (CD) 8 beta. The CD8 glycoprotein plays an essential role in the control of T-cell selection, maturation, and the T-cell receptor (TCR)-mediated response to peptide antigen. CD8 is comprised of alpha and beta subunits and is expressed as either an alpha/alpha or alpha/beta dimer. Both dimeric isoforms can serve as a coreceptor for T cell activation and differentiation, however they have distinct physiological roles, different cellular distributions, unique binding partners, etc. Each CD8 subunit is comprised of an extracellular domain containing a V-type Ig-like domain, a single pass transmembrane portion, and a short intracellular domain. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 52695903   6 QSPSSLSASVGDRVTITCRASQSYAYA-VAWYQQKPGKAPK-----LLIYDAS----YLYSGVPSRFS--GSGSGTDFTL 73
Cdd:cd07700   3 QTPGSLLVQTNQTVKMSCEAKTSPKNTrIYWLRQRQAPSKDshfefLASWDPSkgivYGEGVDQEKLIilSDSDSSRYIL 82

                        90       100       110
                ....*....|....*....|....*....|
gi 52695903  74 TISSLQPEDFATYYCQQAYSSPDTFGQGTK 103
Cdd:cd07700  83 SLMSVKPEDSGTYFCMTVGSPELIFGTGTK 112

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 52695903 112 APSVFIFPPSDEQLkSGTASVVCLLNNFYPREAKVQWKVD-NALQSGNSQ-ESVTeqdsKDSTYSLSSTLTLSKADYEKH 189
Cdd:cd21819   1 APTLFPLVSCGSST-SDPVTVGCLATDFLPDSITFSWTDDnNSLTTGVKTyPSVL----TGGTYTASSQLQVPESEWKSK 75

                        90
                ....*....|.
gi 52695903 190 KVYACEVTHQG 200
Cdd:cd21819  76 ENFYCKVEHPG 86

First immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 4; member of the V-set of IgSF domains; The members here are composed of the first immunoglobulin (Ig) domain of Cluster of Differentiation (CD) 4. CD4 and CD8 are the two primary co-receptor proteins found on the surface of T cells, and the presence of either CD4 or CD8 determines the function of the T cell. CD4 is found on helper T cells, where it is required for the binding of MHC (major histocompatibility complex) class II molecules, while CD8 is found on cytotoxic T cells, where it is required for the binding of MHC class I molecules. CD4 contains four immunoglobulin domains, with the first three included in this hierarchy. The fourth domain has a general Ig architecture, but has slight topological changes in the arrangement of beta strands relative to the other structures in this family and is not specifically included in the hierarchy.

                        10        20        30        40        50        60        70
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*...
gi 52695903  16 GDRVTITCRASQSYAYAVAW---YQQKP-GKAPKLLIYDASYLYSGVPSRFSGSGSGTdFTLTISSLQPEDFATYYCQ 89
Cdd:cd07690   9 GDTAELPCTASQKKSIQFHWknsNQIKIlGNQGSFLTKGPSKLNDRADSRRNLWDQGS-FPLIIKNLKIEDSDTYICE 85

Class II major histocompatibility complex (MHC) beta 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 Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DR. HLA-DR is an MHC class II cell surface receptor encoded by the human leukocyte antigen complex on chromosome 6 region 6p21.31. HLA-DR is also involved in several autoimmune conditions, disease susceptibility, and disease resistance including seronegative-rheumatoid arthritis, penicillamine-induced myasthenia, schizophrenia, Goodpasture syndrome, systemic lupus erythematosus, Alzheimers, tuberculoid leprosy, and Hashimoto's thyroiditis. HLA-DR molecules are upregulated in response to signaling. HLA-DR is an alphabeta heterodimer cell surface receptor, each subunit of which contains two extracellular domains, a membrane-spanning domain, and a cytoplasmic tail. Both alpha and beta chains are anchored in the membrane. The DR beta chain is encoded by 4 loci, however no more than 3 functional loci are present in a single individual, and no more than two on a single chromosome. Sometimes an individual may only possess 2 copies of the same locus, DRB1*. The HLA-DRB1 locus is ubiquitous and encodes a very large number of functionally variable gene products (HLA-DR1 to HLA-DR17). The HLA-DRB3 locus encodes the HLA-DR52 specificity, is moderately variable and is variably associated with certain HLA-DRB1 types. The HLA-DRB4 locus encodes the HLA-DR53 specificity, has some variation, and is associated with certain HLA-DRB1 types. The HLA-DRB5 locus encodes the HLA-DR51 specificity, which is typically invariable, and is linked to the HLA-DR2 types. 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). 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 52695903 113 PSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnaLQSGNSQE----SVTEQDSKDSTYSlssTLTLSKADYEK 188
Cdd:cd21000   4 PKVTVYPAKTQPLQHHNL-LVCSVNGFYPGSIEVRW-----FRNGQEEKagvvSTGLIQNGDWTFQ---TLVMLETVPRS 74

                        90
                ....*....|....*...
gi 52695903 189 HKVYACEVTHQGLSSPVT 206
Cdd:cd21000  75 GEVYTCQVEHPSVTSPLT 92

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 52695903   5 TQSPSSLSASVGDRVTITCR-ASQSYAYAVAWYQQKPG-KAPKLLIYDASYLYSGVPSRFSGSG--SGTDFTLTISSLQP 80
Cdd:cd16088   3 TFSPALLVVTEGANATFTCSfSNTSESFVLNWYRLSPSnQTDKLAAFPEDRSQPGQDWRFRVTQlpNGRDFHMSVVRARR 82

                        90
                ....*....|....*..
gi 52695903  81 EDFATYYCQQAYSSPDT 97
Cdd:cd16088  83 NDSGTYLCGAISLAPKA 99

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) E; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) E. HLA-E is the first human class Ib major histocompatibility complex molecule to be crystallized. Like other MHC class I molecules, HLA-E is a heterodimer consisting of an a heavy chain and light chain beta-2-microglobulin. HLA-E is highly conserved and almost nonpolymorphic, and has recently been shown to be the first specialized ligand for natural killer cell receptors. 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 52695903 119 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNalqSGNSQES--VTEQDSKDSTYSLSSTLTLSKADyekHKVYACEV 196
Cdd:cd21024  14 PISDHE-----ATLRCWALGFYPAEITLTWQQDG---EGHTQDTelVETRPAGDGTFQKWAAVVVPSGE---EQRYTCHV 82

                        90
                ....*....|
gi 52695903 197 THQGLSSPVT 206
Cdd:cd21024  83 QHEGLPEPVT 92

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 52695903 113 PSVFIFPPSDEQLKSGTaSVVCLLNNFYPREAKVQWkvdnaLQSGNSqesVTEqdskdstySLSSTLTLSKADYEKHKV- 191
Cdd:cd21008   3 PEVTVFPKSPVTLGQPN-TLICLVDNIFPPVINITW-----LSNGHS---VTE--------GVSETSFLSKSDHSFLKIs 65

                        90       100
                ....*....|....*....|....*..
gi 52695903 192 -----------YACEVTHQGLSSPVTK 207
Cdd:cd21008  66 yltflpsaddiYDCKVEHWGLDKPLLK 92

Immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin domain of Zn-alpha2-glycoprotein (ZAG). ZAG is a soluble protein that is present in serum and other body fluids. ZAG stimulates lipid degradation in adipocytes and causes the extensive fat losses associated with some advanced cancers. The 2.8 angstrom crystal structure of ZAG resembles a class I major histocompatibility complex (MHC) heavy chain, but ZAG does not bind the class I light chain beta-2-microglobulin. The ZAG structure includes a large groove analogous to class I MHC peptide binding grooves. Instead of a peptide, the ZAG groove contains a nonpeptidic compound that may be implicated in lipid catabolism under normal or pathological conditions. IgC_MHC_I_alpha3; 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
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 52695903 134 CLLNNFYPREAKVQWKvdnalQSGNSQESVTEQD---SKDSTYSLSSTLTLSKADYEKhkvYACEVTHQGLSSPVT 206
Cdd:cd21010  23 CLAYDFYPRGISLHWT-----RAGKVQESESGGDvlpSGNGTYQSWVVVEVPPQDRAP---YSCHVEHSSLAQPLT 90

Signal-regulatory protein (SIRP) immunoglobulin-like domain 2; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig)-like domain in Signal-Regulatory Protein (SIRP), domain 2 (C1 repeat 1). The SIRPs belong to the "paired receptors" class of membrane proteins that comprise several genes coding for proteins with similar extracellular regions, but very different transmembrane/cytoplasmic regions with different (activating or inhibitory) signaling potentials. They are commonly on NK cells, but are also on many myeloid cells. Their extracellular region contains three Immunoglobulin superfamily domains, a single V-set and two C1-set IgSF domains. Their cytoplasmic tails contain either ITIMs or transmembrane regions that have positively charged residues that allow an association with adaptor proteins, such as DAP12/KARAP, containing ITAMs. There are 3 distinct SIRP members: alpha, beta, and gamma. SIRP alpha (also known as CD172a or SRC homology 2 domain-containing protein tyrosine phosphatase substrate 1/Shps-1) is a membrane receptor that interacts with a ligand CD47 expressed on many cells and gives an inhibitory signal through immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic region that interact with phosphatases SHP-1 and SHP-2. SIRP beta has a short cytoplasmic region and associates with a transmembrane adapter protein DAP12 containing immunoreceptor tyrosine-based activation motifs to give an activating signal. SIRP gamma contains a very short cytoplasmic region lacking obvious signaling motifs, but also binds CD47, but with much less affinity.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 52695903 129 TASVVCLLNNFYPREAKVQWKVDNALQSGNsQESVTeqDSKDS-TYSLSST--LTLSKADYekHKVYACEVTHQGLSSPV 205
Cdd:cd05772  19 TVSFTCKSHGFSPRDITLKWFKNGNELSAL-QTTVF--PEGDSvSYSVSSTvqVVLTKDDV--HSQLTCEVAHVTLQAPL 93

                ....*
gi 52695903 206 TKSFN 210
Cdd:cd05772  94 RGTAN 98

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 52695903   8 PSSLSASVGDRVTITCRASQSY----AYAVAWYQQKPGKAPKLLI--YDASYLYSGVPSRF------SGSGSGTDFTLTI 75
Cdd:cd05715   6 PRELNVLNGSDVRLTCTFTSCYtvgdAFSVTWTYQPEGGNTTESMfhYSKGKPYILKVGRFkdrvswAGNPSKKDASIVI 85

                        90
                ....*....|....
gi 52695903  76 SSLQPEDFATYYCQ 89
Cdd:cd05715  86 SNLQFSDNGTYTCD 99

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 52695903 127 SGTASVVCLLNNFYPREAKVQWkvdnaLQSGNSQESVTEQ----DSKDSTYSLSSTLTLskaDYEKHKVYACEVTHQGLS 202
Cdd:cd07698  14 DGESTLRCWALGFYPAEITLTW-----QRDGEDQTQDMELvetrPNGDGTFQKWAAVVV---PSGEEQRYTCHVQHEGLP 85

                ....
gi 52695903 203 SPVT 206
Cdd:cd07698  86 EPLT 89