Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   2 IQMTQSPSSLSASVGDRVTITCKSSQSLLYtssqkNYLAWYQQKPGKAPKLLIYWASTRESGVPSRFSGSGSGTDFTLTI 81
Cdd:cd04980    1 IVMTQSPASLSVSPGERVTISCKASQSISS-----NYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTI 75

                         90       100       110
                 ....*....|....*....|....*....|.
gi 534286604  82 SSLQPEDFATYYCQQYYAYPWTFGQGTKVEI 112
Cdd:cd04980   76 SSVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   2 IQMTQSPSSLSASVGDRVTITCKSSQSLLYtssqkNYLAWYQQKPGKAPKLLIYWASTRESGVPSRFSGSGSGTDFTLTI 81
Cdd:cd04980    1 IVMTQSPASLSVSPGERVTISCKASQSISS-----NYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTI 75

                         90       100       110
                 ....*....|....*....|....*....|.
gi 534286604  82 SSLQPEDFATYYCQQYYAYPWTFGQGTKVEI 112
Cdd:cd04980   76 SSVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604  121 VFIFPPSDEQLKsGTASVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC 200
Cdd:pfam07654   1 VYVFPPSPEELG-KPNTLTCLVTGFYPPDITVTWLKNGQEVT-EGVKTTPPSPNSDWTYQLSSYLTVTPSDWESGDEYTC 78

                  ....*..
gi 534286604  201 EVTHQGL 207
Cdd:pfam07654  79 RVEHEGL 85

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604    19 VTITCKSSQSllytSSQKNYLAWYQQKPGKAPKLLIYWASTR----ESGVPSRFSGSG--SGTDFTLTISSLQPEDFATY 92
Cdd:smart00406   2 VTLSCKFSGS----TFSSYYVSWVRQPPGKGLEWLGYIGSNGssyyQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTY 77

                   ....
gi 534286604    93 YCQQ 96
Cdd:smart00406  78 YCAV 81

Immunoglobulin (Ig) light chain, kappa type, variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, kappa type, variable (V) domain. This group contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   2 IQMTQSPSSLSASVGDRVTITCKSSQSLLYtssqkNYLAWYQQKPGKAPKLLIYWASTRESGVPSRFSGSGSGTDFTLTI 81
Cdd:cd04980    1 IVMTQSPASLSVSPGERVTISCKASQSISS-----NYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTI 75

                         90       100       110
                 ....*....|....*....|....*....|.
gi 534286604  82 SSLQPEDFATYYCQQYYAYPWTFGQGTKVEI 112
Cdd:cd04980   76 SSVEPEDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin (Ig) lambda light chain variable (V) domain; The members here are composed of the immunoglobulin (Ig) light chain, lambda type, variable (V) domain. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda, each composed of a constant domain (CL) and a variable domain (VL). There are five types of heavy chains (alpha, gamma, delta, epsilon, and mu), which determines the type of immunoglobulin formed: IgA, IgG, IgD, IgE, and IgM, respectively. In higher vertebrates, there are two types of light chain, designated kappa and lambda, which seem to be functionally identical, and can associate with any of the heavy chains. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   4 MTQsPSSLSASVGDRVTITCKSSQSllytSSQKNYLAWYQQKPGKAPKLLIYWASTRESGVPSRFSGSGSGTDFTLTISS 83
Cdd:cd04984    2 LTQ-PSSLSVSPGETVTITCTGSSG----NISGNYVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISG 76

                         90       100
                 ....*....|....*....|....*..
gi 534286604  84 LQPEDFATYYCQQYYAYPWTFGQGTKV 110
Cdd:cd04984   77 AQTEDEADYYCQVWDSNSYVFGGGTKL 103

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 534286604 120 SVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESvTEQDSKDSTYSLSSTLTLSKADYEKHKVYA 199
Cdd:cd00098    1 TVTLLPPSPEEKGGGKVTLVCLVSGFYPKDITVTWLKNGVPLTSGVSTS-SPVEPNDGTYSVTSSLTVPPSDWDEGATYT 79

                         90
                 ....*....|....*.
gi 534286604 200 CEVTHQGLSSPVTKSF 215
Cdd:cd00098   80 CVVTHESLKSPLSKTW 95

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 534286604   135 TASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSP 210
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNS-DGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

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 534286604 119 PSVFIFPPSDEQL-KSGTASVVCLLNNFYPREAKVQWKVDN-ALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHK 196
Cdd:cd05768    1 PSVYLLPPPEEELsLNETVTLTCLVKGFYPEDIFVSWLQNGePLPSADYKTTAPVPES-DGSFFVYSKLNVSTADWNSGD 79

                         90       100
                 ....*....|....*....|..
gi 534286604 197 VYACEVTHQGLSSPVT-KSFNR 217
Cdd:cd05768   80 VFSCVVGHEALPLQFTqKSIDK 101

Immunoglobulin V-Type;

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604    19 VTITCKSSQSllytSSQKNYLAWYQQKPGKAPKLLIYWASTR----ESGVPSRFSGSG--SGTDFTLTISSLQPEDFATY 92
Cdd:smart00406   2 VTLSCKFSGS----TFSSYYVSWVRQPPGKGLEWLGYIGSNGssyyQESYKGRFTISKdtSKNDVSLTISNLRVEDTGTY 77

                   ....
gi 534286604    93 YCQQ 96
Cdd:smart00406  78 YCAV 81

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 534286604 118 APSVFIFPPS-DEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQ-ESVTEQDSkDSTYSLSSTLTLSKADYEK- 194
Cdd:cd05769    2 PPTVALFPPSeAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVAtDPQALREN-TSTYSLSSRLRVSATEWFNp 80

                         90       100
                 ....*....|....*....|....*
gi 534286604 195 HKVYACEVTHQGLSSpvTKSFNRGE 219
Cdd:cd05769   81 RNTFTCIVKFYGGTD--TDTWTQGI 103

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) gamma chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the gamma chain of gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigens as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain the standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   4 MTQSPSSLSASVGDRVTITCKSSQSLLYTSsqknYLAWYQQKPGKAPKLLIYWAST----RESGVPS-RFSGS--GSGTD 76
Cdd:cd04982    1 LEQPQLSITREESKSVTISCKVSGIDFSTT----YIHWYRQKPGQALERLLYVSSTsavrKDSGKTKnKFEARkdVGKST 76

                         90       100       110
                 ....*....|....*....|....*....|....*..
gi 534286604  77 FTLTISSLQPEDFATYYCQQYYAYPWT----FGQGTK 109
Cdd:cd04982   77 STLTITNLEKEDSATYYCAYWESGSGYyikvFGSGTK 113

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 534286604 119 PSVFIFPPS-DEQLKSGTASVVCLLNNFYPREAKVQWKVDN--ALQSGNSQESVTEQDSkdsTYSLSSTLTLSKADYEKH 195
Cdd:cd05847    1 PTVQILHSScASTLTSETIQLLCLISGYTPSTIEVEWLVDGqvATLSAASTAPQKEEGG---TFSTTSKLNVTQEDWKSG 77

                         90
                 ....*....|..
gi 534286604 196 KVYACEVTHQGL 207
Cdd:cd05847   78 KTYTCKVTHQGT 89

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) delta chain; The members here are composed of the immunoglobulin (Ig) variable (V) domain of the delta chain of gamma/delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha/beta TCRs, but a small subset contain gamma/delta TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma/delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing, and MHC independently of the bound peptide. Gamma/delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds. The variable domain of gamma/delta TCRs is responsible for antigen recognition and is located at the N-terminus of the receptor. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   3 QMTQSPSSLSASVGDRVTITCKSSqsllyTSSQKNYLAWYQQKPGKAPKLLIYWASTRESGVPSRFSGSGSGTD--FTLT 80
Cdd:cd07706    1 KVTQAQPDVSVQVGEEVTLNCRYE-----TSWTNYYLFWYKQLPSGEMTFLIRQDSSEQNAKSGRYSVNFQKAQksISLT 75

                         90       100       110
                 ....*....|....*....|....*....|....*
gi 534286604  81 ISSLQPEDFATYYCQQYYAYP---WTFGQGTKVEI 112
Cdd:cd07706   76 ISALQLEDSAKYFCALSLPYDtdkLIFGKGTRLTV 110

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 534286604 118 APSVFIF---PPSDEQLKsgtasVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADyeK 194
Cdd:cd21029    2 KPRVRLSsrpSPGDGHLQ-----LSCHVTGFYPRPIEVTWLRDGQEQM-DGTQSGGILPNHDGTYQLRKTLDIAPGE--G 73

                         90
                 ....*....|....*...
gi 534286604 195 HKvYACEVTHQGLSSPVT 212
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 534286604 118 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKV 197
Cdd:cd04985    1 APTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWQKNTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSGEV 80

                         90
                 ....*....|....*.
gi 534286604 198 YACEVTHQGLSSPVTK 213
Cdd:cd04985   81 YKCQVQHSASNSKQEK 96

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

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604   7 SPSSLSASVGDRVTITCkssqslLYTSSQKNYLAWYQQKPGKAPKL--LIYWASTRESGVP-----SRFSGSGSGTDFTL 79
Cdd:cd05720    4 SPRKRDAQLGQKVELVC------EVLNSVPQGCSWLFQPRGSAPQPtfLLYLSSSNKTKWAegldsKRFSGSRSGSSYVL 77

                         90
                 ....*....|....*
gi 534286604  80 TISSLQPEDFATYYC 94
Cdd:cd05720   78 TLKDFRKEDEGYYFC 92

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 534286604 117 AAPSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnalqSGNSQESVTEQDSK------DSTYSLSSTL--TLS 188
Cdd:cd21001    2 VEPTVTISPSRTEALNHHNL-LVCSVTDFYPGQIKVRW-------FRNDQEETAGVVSTplirngDWTFQILVMLemTPQ 73

                         90       100
                 ....*....|....*....|....
gi 534286604 189 KADyekhkVYACEVTHQGLSSPVT 212
Cdd:cd21001   74 RGD-----VYTCHVEHPSLQSPIT 92

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

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604 119 PSVFIFPPSDEQLKSgTASVVCLLNNFYPREAKVQWKVDNALQsGNSQESVTEQDSKDSTYSLSSTL--TLSKADyekhk 196
Cdd:cd05766    4 PSVKVSPTKTGPLEH-PNLLVCSVTGFYPAEIEVKWFRNGQEE-TAGVVSTELIPNGDWTFQILVMLetTPRRGD----- 76

                         90
                 ....*....|....*.
gi 534286604 197 VYACEVTHQGLSSPVT 212
Cdd:cd05766   77 VYTCQVEHSSLQSPLT 92

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 534286604 118 APSVFIFPPSDEQLkSGTASVVCLLNNFYPREAKVQWKVD-NALQSGNSQ-ESVTeqdsKDSTYSLSSTLTLSKADYEKH 195
Cdd:cd21819    1 APTLFPLVSCGSST-SDPVTVGCLATDFLPDSITFSWTDDnNSLTTGVKTyPSVL----TGGTYTASSQLQVPESEWKSK 75

                         90
                 ....*....|.
gi 534286604 196 KVYACEVTHQG 206
Cdd:cd21819   76 ENFYCKVEHPG 86

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 534286604 118 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDnALQSGNSQESVTEQDSkdSTYSLSSTLTLSKADYEKhKV 197
Cdd:cd21817    1 APSVFPLAPCCKSTNGSSVTLGCLVTGYFPEPVTVTWNSG-SLTSGVKTFPAVLQSS--GLYTTSSQVTVPSSSWGS-QT 76

                         90
                 ....*....|....*.
gi 534286604 198 YACEVTHQGLSSPVTK 213
Cdd:cd21817   77 FTCNVEHKPSSTKVDK 92

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) I-E; 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) I-E. 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 molecules have the same basic features insofar as peptide loading and presentation, although each interacts with distinctly different sets of peptides. They also differ in that there is a relatively high incidence of deletion of the I-E gene in both inbred strains of mice as well as wild mice and the lack of the reverse situation i.e. the deletion of I-A genes. A detailed structural understanding of the similarities and differences between I-A and the paralogous I-E could help illuminate the respective roles these molecules play 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. 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 534286604 119 PSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnaLQSGNSQES--VTEQDSKDSTYSLSsTLTLSKADYEKHK 196
Cdd:cd20998    7 PTVTVYPTKTQPLEHHNL-LVCSVSDFYPGNIEVRW-----FRNGKEEKTgiVSTGLVRNGDWTFQ-TLVMLETVPQSGE 79

                         90
                 ....*....|....*.
gi 534286604 197 VYACEVTHQGLSSPVT 212
Cdd:cd20998   80 VYTCQVEHPSLTDPVT 95

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 534286604 119 PSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnaLQSGNSQE----SVTEQDSKDSTYSlssTLTLSKADYEK 194
Cdd:cd21000    4 PKVTVYPAKTQPLQHHNL-LVCSVNGFYPGSIEVRW-----FRNGQEEKagvvSTGLIQNGDWTFQ---TLVMLETVPRS 74

                         90
                 ....*....|....*...
gi 534286604 195 HKVYACEVTHQGLSSPVT 212
Cdd:cd21000   75 GEVYTCQVEHPSVTSPLT 92

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 534286604 125 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNalqSGNSQES--VTEQDSKDSTYSLSSTLTLSKADyekHKVYACEV 202
Cdd:cd21024   14 PISDHE-----ATLRCWALGFYPAEITLTWQQDG---EGHTQDTelVETRPAGDGTFQKWAAVVVPSGE---EQRYTCHV 82

                         90
                 ....*....|
gi 534286604 203 THQGLSSPVT 212
Cdd:cd21024   83 QHEGLPEPVT 92

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 534286604    3 QMTQSPSSLSASVGDRVTITCKSsqsllyTSSQKNYLAWYqqKPGKApklliywasTRESGVPSRFSGSGSGTdftLTIS 82
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCEA------TGSPPPTITWY--KNGEP---------ISSGSTRSRSLSGSNST---LTIS 62

                          90
                  ....*....|...
gi 534286604   83 SLQPEDFATYYCQ 95
Cdd:pfam13927  63 NVTRSDAGTYTCV 75

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 534286604 119 PSVFIFPPSDEQLKSGTaSVVCLLNNFYPREAKVQWkvdnaLQSGNSqesVTEqdskdstySLSSTLTLSKADYEKHKV- 197
Cdd:cd21008    3 PEVTVFPKSPVTLGQPN-TLICLVDNIFPPVINITW-----LSNGHS---VTE--------GVSETSFLSKSDHSFLKIs 65

                         90       100
                 ....*....|....*....|....*..
gi 534286604 198 -----------YACEVTHQGLSSPVTK 213
Cdd:cd21008   66 yltflpsaddiYDCKVEHWGLDKPLLK 92

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) F; 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 alpha chain F (HLA-F). HLA-F, encoded by the HLA-F gene in humans, belongs to the non-classical HLA class I heavy chain paralogs. This class I molecule mainly exists as a heterodimer associated with the invariant light chain beta-2-microglobulin. HLA-F molecules can interact with both activating and inhibitory receptors on immune cells, such as NK cells, and can present a diverse panel of peptides. 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 534286604 125 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNALQSGNSqESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTH 204
Cdd:cd21023   14 PISDHE-----ATLRCWALGFYPAEITLTWQRDGEEQTQDT-ELVETRPAGDGTFQKWAAVVVPPGEEQR---YTCHVQH 84

                 ....*..
gi 534286604 205 QGLSSPV 211
Cdd:cd21023   85 EGLPQPL 91

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of H2-Dd; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class Ia major histocompatibility complex (MHC) immunoglobulin domain of H2-Dd. Mouse MHC is composed of 11 subclasses. It includes the classical MHC class I (MHC-Ia) that comprises H-2D, H-2K and H-2L subclasses, the non-classical MHC class I (MHCIb) that comprises H-2Q, H-2M and H-2T subclasses, the classical MHC class II (MHC-IIa) that includes H-2A(I-A) and H-2E(I-E) subclasses, and the non-classical MHC class II (MHC-IIb) comprises H-2M and H-2O. H-2K, H-2D, and H-2L are 80 to 90% homologous at the amino acid level yet appear to be involved in different recognition reactions and are differentially expressed on lymphoid cells. 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 534286604 134 GTASVVCLLNNFYPREAKVQWKVdNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTHQGLSSPVT 212
Cdd:cd21020   18 GDVTLRCWALGFYPADITLTWQL-NGEELTQEMELVETRPAGDGTFQKWASVVVPLGKEQK---YTCHVEHEGLPEPLT 92

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) I-A; 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) 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 molecules have the same basic features insofar as peptide loading and presentation, although each interacts with distinctly different sets of peptides. They also differ in that there is a relatively high incidence of deletion of the I-E a gene in both inbred strains of mice as well as wild mice and the lack of the reverse situation i.e. the deletion of I-A genes. A detailed structural understanding of the similarities and differences between I-A and the paralogous I-E could help illuminate the respective roles these molecules play 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. 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 534286604 118 APSVFIFPPSDEQLKSGTaSVVCLLNNFYPREAKVQWkVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEkhkV 197
Cdd:cd21006    2 APQATVFPKSPVLLGQPN-TLICFVDNIFPPVINITW-LRNSKSVTDGVYETSFLVNRDHSFHKLSYLTFIPSDDD---I 76

                         90
                 ....*....|....*....
gi 534286604 198 YACEVTHQGLSSPVTKSFN 216
Cdd:cd21006   77 YDCKVEHWGLEEPVLKHWE 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) G; 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) G. HLA-G histocompatibility antigen (also known as human leukocyte antigen G ; HLA-G) is a protein that in humans is encoded by the HLA-G gene. HLA-G belongs to the HLA nonclassical class I heavy chain paralogs. This class I molecule is a heterodimer consisting of a heavy chain and light chain, beta-2-microglobulin. The heavy chain is anchored in the membrane. HLA-G may play a role in immune tolerance in pregnancy, being expressed in the placenta by extravillous trophoblast cells (EVT), while the classical MHC class I genes (HLA-A and HLA-B) are not. Immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class I and class II. 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. MHC class II molecules play a key role in the initiation of the antigen-specific immune repose. 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
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 534286604 136 ASVVCLLNNFYPREAKVQWKVDNALQSGNSqESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTHQGLSSPV 211
Cdd:cd21022   19 ATLRCWALGFYPAEIILTWQRDGEDQTQDV-ELVETRPAGDGTFQKWAAVVVPSGEEQR---YTCHVQHEGLPEPL 90