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 1938929140   2 IQMTQSPSSLSASLGERVSLTCRASQEING-YLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGSRSGSDYSLTISSLES 80
Cdd:cd04980     1 IVMTQSPASLSVSPGERVTISCKASQSISSnYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTISSVEP 80

                          90       100
                  ....*....|....*....|....*.
gi 1938929140  81 EDFADYYCLQYASYPRTFGGGTKVEI 106
Cdd:cd04980    81 EDAAVYYCQQGYTFPYTFGGGTKLEI 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 1938929140   2 IQMTQSPSSLSASLGERVSLTCRASQEING-YLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGSRSGSDYSLTISSLES 80
Cdd:cd04980     1 IVMTQSPASLSVSPGERVTISCKASQSISSnYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTISSVEP 80

                          90       100
                  ....*....|....*....|....*.
gi 1938929140  81 EDFADYYCLQYASYPRTFGGGTKVEI 106
Cdd:cd04980    81 EDAAVYYCQQGYTFPYTFGGGTKLEI 106

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140 115 VFIFPPSDEQLKsGTASVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC 194
Cdd:pfam07654   1 VYVFPPSPEELG-KPNTLTCLVTGFYPPDITVTWLKNGQEVT-EGVKTTPPSPNSDWTYQLSSYLTVTPSDWESGDEYTC 78

                  ....*..
gi 1938929140 195 EVTHQGL 201
Cdd:pfam07654  79 RVEHEGL 85

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

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140    8 PSSLSASLGERVSLTCRASQEINGYLGWLQQKPdgtiKRLIYaastlhsgvPKRFSGSRSGSDYSLTISSLESEDFADYY 87
Cdd:smart00410   1 PPSVTVKEGESVTLSCEASGSPPPEVTWYKQGG----KLLAE---------SGRFSVSRSGSTSTLTISNVTPEDSGTYT 67

                           90
                   ....*....|....*....
gi 1938929140   88 CLQYASYPRTFgGGTKVEI 106
Cdd:smart00410  68 CAATNSSGSAS-SGTTLTV 85

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 1938929140   2 IQMTQSPSSLSASLGERVSLTCRASQEING-YLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGSRSGSDYSLTISSLES 80
Cdd:cd04980     1 IVMTQSPASLSVSPGERVTISCKASQSISSnYLAWYQQKPGQAPKLLIYYASTLHSGVPSRFSGSGSGTDFTLTISSVEP 80

                          90       100
                  ....*....|....*....|....*.
gi 1938929140  81 EDFADYYCLQYASYPRTFGGGTKVEI 106
Cdd:cd04980    81 EDAAVYYCQQGYTFPYTFGGGTKLEI 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 1938929140   4 MTQsPSSLSASLGERVSLTCRASQEING--YLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGSRSGSDYSLTISSLESE 81
Cdd:cd04984     2 LTQ-PSSLSVSPGETVTITCTGSSGNISgnYVNWYQQKPGSAPRYLIYEDKHRPSGIPDRFSGSKSGNTASLTISGAQTE 80

                          90       100
                  ....*....|....*....|...
gi 1938929140  82 DFADYYCLQYASYPRTFGGGTKV 104
Cdd:cd04984    81 DEADYYCQVWDSNSYVFGGGTKL 103

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140 115 VFIFPPSDEQLKsGTASVVCLLNNFYPREAKVQWKVDNALQSgNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC 194
Cdd:pfam07654   1 VYVFPPSPEELG-KPNTLTCLVTGFYPPDITVTWLKNGQEVT-EGVKTTPPSPNSDWTYQLSSYLTVTPSDWESGDEYTC 78

                  ....*..
gi 1938929140 195 EVTHQGL 201
Cdd:pfam07654  79 RVEHEGL 85

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*.
gi 1938929140  129 TASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSkDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSP 204
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNS-DGTYFLSSYLTVPASTWESGDVYTCQVTHEGLKEP 75

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 1938929140 112 APSVFIFPPS-DEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQ-ESVTEQDSkDSTYSLSSTLTLSKADYEK- 188
Cdd:cd05769     2 PPTVALFPPSeAEIRNKRKATLVCLATGFYPDHVSLSWKVNGKEVKDGVAtDPQALREN-TSTYSLSSRLRVSATEWFNp 80

                          90       100
                  ....*....|....*....|....*
gi 1938929140 189 HKVYACEVTHQGLSSpvTKSFNRGE 213
Cdd:cd05769    81 RNTFTCIVKFYGGTD--TDTWTQGI 103

Immunoglobulin (Ig) variable (V) domain of T-cell receptor (TCR) alpha chain and similar proteins; The members here are composed of the immunoglobulin (Ig) variable domain of the alpha chain of alpha/beta T-cell antigen receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes, and are composed of alpha and beta, or gamma and delta polypeptide chains with variable (V) and constant (C) regions. This group represents the variable domain of the alpha chain of TCRs and also includes the variable domain of delta chains of TCRs. Alpha/beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. The variable domain of TCRs is responsible for antigen recognition, and is located at the N-terminus of the receptor. Gamma/delta TCRs recognize intact protein antigens directly without antigen processing and recognize MHC independently of the bound peptide. Members of this group contain standard Ig superfamily V-set AGFCC'C"/DEB domain topology.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140   5 TQSPSSLSASLGERVSLTCRASQEINGYLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGS--RSGSDYSLTISSLESED 82
Cdd:cd04983     2 TQSPQSLSVQEGENVTLNCNYSTSTFYYLFWYRQYPGQGPQFLIYISSDSGNKKKGRFSATldKSRKSSSLHISAAQLSD 81

                          90       100
                  ....*....|....*....|....*...
gi 1938929140  83 FADYYC---LQYASYPRTFGGGTKVEIK 107
Cdd:cd04983    82 SAVYFCalsESGGTGKLTFGKGTRLTVE 109

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 1938929140 113 PSVFIFPPSDEQL-KSGTASVVCLLNNF--YPrEAKVQWKVdnalQSGNSQESVTEQDSK--DSTYSLSSTLTLSKADYE 187
Cdd:cd07696     1 VSVFLIPPSPKDLfLTKSAKVTCLVVDLtsIE-EVNVTWSR----EDGNEVLASTTNPEKhyNATLSVVSTLTVCADDWD 75

                          90       100
                  ....*....|....*....|.
gi 1938929140 188 KHKVYACEVTHQGLSSPVTKS 208
Cdd:cd07696    76 NGKTFKCKVTHPDLPSPIVKS 96

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 1938929140   6 QSPSSLSASLGERVSLTCRAS---QEINGYLGWLQQKPDGTIKRLIYAASTL--HSGVPKRFS--GSRSGSDYSLTISSL 78
Cdd:pfam07686   1 QTPREVTVALGGSVTLPCTYSssmSEASTSVYWYRQPPGKGPTFLIAYYSNGseEGVKKGRFSgrGDPSNGDGSLTIQNL 80

                          90       100
                  ....*....|....*....|....*...
gi 1938929140  79 ESEDFADYYCLQYASYPRTFGGGTKVEI 106
Cdd:pfam07686  81 TLSDSGTYTCAVIPSGEGVFGKGTRLTV 108

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140   3 QMTQSPSSLSASLGERVSLTCR-ASQEINGYLGWLQQKPDGTIKRLIYAASTLHSGVPKRFSGS--RSGSDYSLTISSLE 79
Cdd:cd07706     1 KVTQAQPDVSVQVGEEVTLNCRyETSWTNYYLFWYKQLPSGEMTFLIRQDSSEQNAKSGRYSVNfqKAQKSISLTISALQ 80

                          90       100       110
                  ....*....|....*....|....*....|
gi 1938929140  80 SEDFADYYCLQYASYPR---TFGGGTKVEI 106
Cdd:cd07706    81 LEDSAKYFCALSLPYDTdklIFGKGTRLTV 110

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 1938929140   4 MTQSPSSLSASLGERVSLTCRASQEI--NGYLGWLQQKPDGTIKRLIYAAST-----LHSGVPKRFSGSRSG--SDYSLT 74
Cdd:cd04982     1 LEQPQLSITREESKSVTISCKVSGIDfsTTYIHWYRQKPGQALERLLYVSSTsavrkDSGKTKNKFEARKDVgkSTSTLT 80

                          90       100       110
                  ....*....|....*....|....*....|...
gi 1938929140  75 ISSLESEDFADYYC----LQYASYPRTFGGGTK 103
Cdd:cd04982    81 ITNLEKEDSATYYCayweSGSGYYIKVFGSGTK 113

Signal-regulatory protein (SIRP) immunoglobulin-like domain 3; 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 3 (C1 repeat 2). 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 that 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 1938929140 132 VVCLLNNFYPREAKVQWkvdnaLQSGNsqESVTEQDS-----KDSTYSLSSTLTLSKADYEKHKVYACEVTHQGlSSPVT 206
Cdd:cd16085    20 VTCQVEKFYPQRLQLTW-----LENGN--VSRTETPStltvnKDGTYNWTSWLLVNVSAHREDVVLTCQVEHDG-QPAVT 91

                  ..
gi 1938929140 207 KS 208
Cdd:cd16085    92 KN 93

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 1938929140 112 APSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKV 191
Cdd:cd04985     1 APTVFPLQSATKSQSNGPVALGCLISDYFPESITVSWQKNTNSITSGFTRTFPVVLRSGGDYSCSSQLTVPLQEWNSGEV 80

                          90
                  ....*....|....*.
gi 1938929140 192 YACEVTHQGLSSPVTK 207
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 1938929140   7 SPSSLSASLGERVSLTCRASQEINGYLGWLQQKPDGTIKR--LIYAASTLHSGVP-----KRFSGSRSGSDYSLTISSLE 79
Cdd:cd05720     4 SPRKRDAQLGQKVELVCEVLNSVPQGCSWLFQPRGSAPQPtfLLYLSSSNKTKWAegldsKRFSGSRSGSSYVLTLKDFR 83

                  ....*....
gi 1938929140  80 SEDFADYYC 88
Cdd:cd05720    84 KEDEGYYFC 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 1938929140 111 AAPSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnalqSGNSQESVTEQDSK------DSTYSLSSTL--TLS 182
Cdd:cd21001     2 VEPTVTISPSRTEALNHHNL-LVCSVTDFYPGQIKVRW-------FRNDQEETAGVVSTplirngDWTFQILVMLemTPQ 73

                          90       100
                  ....*....|....*....|....
gi 1938929140 183 KADyekhkVYACEVTHQGLSSPVT 206
Cdd:cd21001    74 RGD-----VYTCHVEHPSLQSPIT 92

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of the major histocompatibility complex (MHC) class II alpha 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 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 1938929140 112 APSVFIFPPSDEQL-KSGTasVVCLLNNFYPREAKVQWkvdnaLQSGnsqESVTEQDSkDSTYSLSSTLTLSKADY---- 186
Cdd:cd05767     2 PPEVTVFPKSPVELgEPNT--LICFVDNFFPPVINVTW-----LRNG---QPVTDGVS-ETVFLPREDHSFRKFSYlpft 70

                          90       100
                  ....*....|....*....|..
gi 1938929140 187 -EKHKVYACEVTHQGLSSPVTK 207
Cdd:cd05767    71 pSEGDIYDCRVEHWGLEEPLLK 92

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) B and similar proteins; 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 human leukocyte antigen (HLA) B and similar proteins. The classical class I molecules (HLA-A, -B, and -C) are responsible for the presentation of endogenous antigen to CD8+ T cells. The receptor is a heterodimer, and is composed of a heavy alpha chain and smaller beta chain. The alpha chain is encoded by a variant HLA-B gene, and the beta chain (beta-2-microglobulin) is an invariant beta-2-microglobulin molecule. The beta-2-microglobulin protein is coded for by a separate region of the human genome. Human leukocyte antigen (HLA) B*3501 (B35) is a common human allele involved in mediating protective immunity against HIV. 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 1938929140 119 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNALQSGNSqESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTH 198
Cdd:cd21026    14 PISDHE-----ATLRCWALGFYPAEITLTWQRDGEDQTQDT-ELVETRPAGDRTFQKWAAVVVPSGEEQR---YTCHVQH 84

                  ....*...
gi 1938929140 199 QGLSSPVT 206
Cdd:cd21026    85 EGLPKPLT 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 1938929140 119 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNalqSGNSQES--VTEQDSKDSTYSLSSTLTLSKADyekHKVYACEV 196
Cdd:cd21024    14 PISDHE-----ATLRCWALGFYPAEITLTWQQDG---EGHTQDTelVETRPAGDGTFQKWAAVVVPSGE---EQRYTCHV 82

                          90
                  ....*....|
gi 1938929140 197 THQGLSSPVT 206
Cdd:cd21024    83 QHEGLPEPVT 92

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) A; 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 human leukocyte antigen (HLA) A. The classical class I molecules (HLA-A, -B, and -C) are responsible for the presentation of endogenous antigen to CD8+ T cells. The receptor is a heterodimer, and is composed of a heavy alpha chain and smaller beta chain. The alpha chain is encoded by a variant HLA-A gene, and the beta chain (beta-2-microglobulin) is an invariant beta-2-microglobulin molecule. The beta-2-microglobulin protein is coded for by a separate region of the human genome. HLA-A2 is associated with spontaneous abortions, HIV, and Hodgkin lymphoma. 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 1938929140 130 ASVVCLLNNFYPREAKVQWKVDNALQSGNSqESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTHQGLSSPVT 206
Cdd:cd21027    20 ATLRCWALSFYPAEITLTWQRDGEDQTQDT-ELVETRPAGDGTFQKWAAVVVPSGQEQR---YTCHVQHEGLPKPLT 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 1938929140 113 PSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWkvdnaLQSGNSQES--VTEQDSKDSTYSLSsTLTLSKADYEKHK 190
Cdd:cd20998     7 PTVTVYPTKTQPLEHHNL-LVCSVSDFYPGNIEVRW-----FRNGKEEKTgiVSTGLVRNGDWTFQ-TLVMLETVPQSGE 79

                          90
                  ....*....|....*.
gi 1938929140 191 VYACEVTHQGLSSPVT 206
Cdd:cd20998    80 VYTCQVEHPSLTDPVT 95

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 1938929140 119 PPSDEQlksgtASVVCLLNNFYPREAKVQWKVDNALQSGNSqESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTH 198
Cdd:cd21023    14 PISDHE-----ATLRCWALGFYPAEITLTWQRDGEEQTQDT-ELVETRPAGDGTFQKWAAVVVPPGEEQR---YTCHVQH 84

                  ....*..
gi 1938929140 199 QGLSSPV 205
Cdd:cd21023    85 EGLPQPL 91

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DM; 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) DM. Human HLA-DM plays a critical role in antigen presentation to CD4 T cells by catalyzing the exchange of peptides bound to MHC class II molecules. Type 1 diabetes is correlated with DM activation and it is also implicated in viral infections such as herpes simplex virus, celiac disease, multiple sclerosis, other autoimmune diseases, and leukemia. 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 1938929140 113 PSVFIFPPsdeQLKSGTASVV--CLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTL--SKADyek 188
Cdd:cd21002     4 PSVRVAPT---TPFNTREPVMlaCHVWGFYPADVTITWLKNGDPVAPHSSAPKTAQPNGDWTYQTQVTLAVtpSPGD--- 77

                          90
                  ....*....|....*....
gi 1938929140 189 hkVYACEVTHQGLSSPVTK 207
Cdd:cd21002    78 --TYTCSVQHASLPEPLLE 94

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 1938929140 128 GTASVVCLLNNFYPREAKVQWKVdNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKhkvYACEVTHQGLSSPVT 206
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 1938929140 112 APSVFIFPPSDEQLKSGTaSVVCLLNNFYPREAKVQWkVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEkhkV 191
Cdd:cd21006     2 APQATVFPKSPVLLGQPN-TLICFVDNIFPPVINITW-LRNSKSVTDGVYETSFLVNRDHSFHKLSYLTFIPSDDD---I 76

                          90
                  ....*....|....*....
gi 1938929140 192 YACEVTHQGLSSPVTKSFN 210
Cdd:cd21006    77 YDCKVEHWGLEEPVLKHWE 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of Qa-2; 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 QA-2. Qa-2 is a nonclassical MHC Ib antigen, which has been implicated in both innate and adaptive immune responses, as well as embryonic development. Qa-2 has an unusual peptide binding specificity in that it requires two dominant C-terminal anchor residues and is capable of associating with a substantially more diverse array of peptide sequences than other nonclassical MHC. 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 1938929140 128 GTASVVCLLNNFYPREAKVQWKVdNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKAdyeKHKVYACEVTHQGLSSPVT 206
Cdd:cd21014    17 GAVTLRCWALGFYPADITLTWQL-NGEELTQDMELVETRPAGDGTFQKWASVVVPLG---KEQNYTCHVNHEGLPEPLT 91

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140   3 QMTQSPSSLSASLGERVSLTCRASqeinGYlgwlqqkPDGTIKRLIYAASTLHSGVPKRFSGSRSGsdySLTISSLESED 82
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCEAT----GS-------PPPTITWYKNGEPISSGSTRSRSLSGSNS---TLTISNVTRSD 68

                  ....*.
gi 1938929140  83 FADYYC 88
Cdd:pfam13927  69 AGTYTC 74

Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the Class II major histocompatibility complex (MHC) beta chain immunoglobulin domain of histocompatibility antigen (HLA) DP. HLA class II histocompatibility antigen, DP(W2) beta chain is a protein that in humans is encoded by the HLA-DPB1 gene. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DP is an alphabeta heterodimer cell-surface receptor. Each DP subunit (alpha-subunit, beta-subunit) is composed of a alpha-helical N-terminal domain, an IgG-like beta sheet, a membrane spanning domain, and a cytoplasmic domain. The alpha-helical domain forms the sides of the peptide binding groove. The beta sheet regions form the base of the binding groove and the bulk of the molecule as well as the inter-subunit (non-covalent) binding region. Individuals carrying the MHCII allele, HLA-DP2, are at risk for chronic beryllium disease (CBD), a debilitating inflammatory lung condition caused by the reaction of CD4 T cells to inhaled beryllium. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1938929140 113 PSVFIFPPSDEQLKSGTAsVVCLLNNFYPREAKVQWKVdnalqsgNSQE------SVTEQDSKDSTYSLSSTLTLSKady 186
Cdd:cd21003     4 PKVNVSPSKKGPLQHHNL-LVCHVTDFYPGNIQVRWFL-------NGQEetagvvSTNLIHNGDWTFQILVMLEMTP--- 72

                          90       100
                  ....*....|....*....|
gi 1938929140 187 EKHKVYACEVTHQGLSSPVT 206
Cdd:cd21003    73 QQGDVYTCQVEHPSLDSPVT 92