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 24797074 116 DPPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd05767   1 VPPEVTVFPKSPVELGEPNTLICFVDNFFPPVINVTWLRNGQPVTDGVSETVFLPREDHSFRKFSYLPFTPSEGDIYDCR 80

                        90
                ....*....|....*
gi 24797074 196 VEHWGLDQPLLKHWE 210
Cdd:cd05767  81 VEHWGLEEPLLKHWE 95

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 24797074 116 DPPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd05767   1 VPPEVTVFPKSPVELGEPNTLICFVDNFFPPVINVTWLRNGQPVTDGVSETVFLPREDHSFRKFSYLPFTPSEGDIYDCR 80

                        90
                ....*....|....*
gi 24797074 196 VEHWGLDQPLLKHWE 210
Cdd:cd05767  81 VEHWGLEEPLLKHWE 95

Class II histocompatibility antigen, alpha domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074    35 DHVSTY-AAFVQTHRPTGEFMFEFDEDEMFYVDLDKKETVWHLEEFGQAFSFEAQGGLANIAILNNNLNTLIQRSNHTQA 113
Cdd:pfam00993   1 DHVGIYgCSFYQSYDPSGEYMFEFDGDELFYVDFKKKETVWRLPEFADFASFDPQGALANIAVCKNNLDILIKRSNSTPA 80

                  .
gi 24797074   114 T 114
Cdd:pfam00993  81 T 81

Immunoglobulin C-Type;

                           10        20        30        40        50        60        70
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 24797074    133 PNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTF---VPSAEDFYDCRVEHWGLDQP 204
Cdd:smart00407   1 KATLVCLVSGFYPPDITVTWLRNGQEVTEGVSTTDPLKNSDGTYFLSSYLTVpasTWESGDVYTCQVTHEGLKEP 75

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 24797074 116 DPPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd05767   1 VPPEVTVFPKSPVELGEPNTLICFVDNFFPPVINVTWLRNGQPVTDGVSETVFLPREDHSFRKFSYLPFTPSEGDIYDCR 80

                        90
                ....*....|....*
gi 24797074 196 VEHWGLDQPLLKHWE 210
Cdd:cd05767  81 VEHWGLEEPLLKHWE 95

HLA class II histocompatibility antigen DO alpha; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the nonclassical MHC class II (MHCII) protein, HLA-DO, which binds HLA-DM and influences the repertoire of peptides presented by MHCII proteins. In complex with HLA-DM, HLA-DO adopts a classical MHCII structure, with alterations near the a subunit's 310 helix. HLA-DO binds to HLA-DM at the same sites implicated in MHCII interaction, and kinetic analysis showed that HLA-DO acts as a competitive inhibitor by acting as a substrate mimic. Though more remains to be elucidated about the function of HLA-DO, its unique distribution in the mammalian body namely, the exclusive expression of HLA-DO in B cells, thymic medullary epithelial cells, and dendritic cells indicate that it may be of physiological importance and has inspired further research. 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 24797074 117 PPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRV 196
Cdd:cd21004   2 PPRVTVLPKSRVELGQPNILICIVDNIFPPVINITWLRNGQTVTEGVAQTSFYSQPDHLFRKFHYLPFVPSAEDVYDCKV 81

                        90
                ....*....|....
gi 24797074 197 EHWGLDQPLLKHWE 210
Cdd:cd21004  82 EHWGLDRPLLRHWE 95

Class II major histocompatibility complex (MHC) alpha 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 immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) I-E. 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 24797074 118 PEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRVE 197
Cdd:cd21005   3 PEVTVLSRSPVNLGEPNILICFIDKFSPPVVNVTWLRNGRPVTEGVSETVFLPRDDHLFRKFHYLTFLPSTDDFYDCEVD 82

                        90
                ....*....|...
gi 24797074 198 HWGLDQPLLKHWE 210
Cdd:cd21005  83 HWGLEEPLRKHWE 95

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074   120 VTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPS---AEDFYDCRV 196
Cdd:pfam07654   1 VYVFPPSPEELGKPNTLTCLVTGFYPPDITVTWLKNGQEVTEGVKTTPPSPNSDWTYQLSSYLTVTPSdweSGDEYTCRV 80

                  ....*
gi 24797074   197 EHWGL 201
Cdd:pfam07654  81 EHEGL 85

Class II histocompatibility antigen, alpha domain; Class II MHC glycoproteins are expressed on the surface of antigen-presenting cells (APC), including macrophages, dendritic cells and B cells. MHC II proteins present peptide antigens that originate extracellularly from foreign bodies such as bacteria. Proteins from the pathogen are degraded into peptide fragments within the APC, which sequesters these fragments into the endosome so they can bind to MHC class II proteins, before being transported to the cell surface. MHC class II receptors display antigens for recognition by helper T cells (stimulate development of B cell clones) and inflammatory T cells (cause the release of lymphokines that attract other cells to site of infection).

                           10        20        30        40        50        60        70        80
                   ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074     37 VSTYAAFV--QTHRPTGEFMFEFDEDEMFYVDLDKKETVWHLEEFGQAFSFEAQGGLANIAILNNNLNTLIQRSNHTQAT 114
Cdd:smart00920   1 VGTYGHIVycSDYDPSGEYMFEFDGDELFYVDFDKKETVWRLPEFADFASFDYQGALADIAVCKANLDILIKRSNSTPAT 80

                   .
gi 24797074    115 N 115
Cdd:smart00920  81 N 81

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 24797074 117 PPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRV 196
Cdd:cd05766   3 QPSVKVSPTKTGPLEHPNLLVCSVTGFYPAEIEVKWFRNGQEETAGVVSTELIPNGDWTFQILVMLETTPRRGDVYTCQV 82

                        90
                ....*....|....
gi 24797074 197 EHWGLDQPLLKHWE 210
Cdd:cd05766  83 EHSSLQSPLTVDWR 96

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

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 117 PPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGElVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRV 196
Cdd:cd05770   2 TPKVQVYSRFPAENGKPNVLNCYVSGFHPPDIEIRLLKNGV-KIEDVEQSDLSFSKDWTFYLLKYTEFTPTKGDEYACRV 80

                        90
                ....*....|....
gi 24797074 197 EHWGLDQPLLKHWE 210
Cdd:cd05770  81 RHNTLSEPKIYKWD 94

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 24797074 117 PPEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRV 196
Cdd:cd21003   3 QPKVNVSPSKKGPLQHHNLLVCHVTDFYPGNIQVRWFLNGQEETAGVVSTNLIHNGDWTFQILVMLEMTPQQGDVYTCQV 82

                        90
                ....*....|...
gi 24797074 197 EHWGLDQPLLKHW 209
Cdd:cd21003  83 EHPSLDSPVTVEW 95

Class II major histocompatibility complex (MHC) alpha 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 immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) DM. Human HLA-DM, also known as H2-M in mice, plays a critical role in antigen presentation to CD4 T cells by catalyzing the exchange of peptides bound to MHC class II molecules. 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 24797074 118 PEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVtEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRVE 197
Cdd:cd21009   3 PIAEVFTLKPLEFGKPNTLVCFVSNLFPPMLTVNWQLHSVPV-EGFGPTFVSAVDGLSFQAFSYLNFTPEPSDIFSCIVT 81

                .
gi 24797074 198 H 198
Cdd:cd21009  82 H 82

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 24797074 118 PEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRVE 197
Cdd:cd20998   7 PTVTVYPTKTQPLEHHNLLVCSVSDFYPGNIEVRWFRNGKEEKTGIVSTGLVRNGDWTFQTLVMLETVPQSGEVYTCQVE 86

                        90
                ....*....|...
gi 24797074 198 HWGLDQPLLKHWE 210
Cdd:cd20998  87 HPSLTDPVTVEWK 99

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 24797074 118 PEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCRVE 197
Cdd:cd21001   4 PTVTISPSRTEALNHHNLLVCSVTDFYPGQIKVRWFRNDQEETAGVVSTPLIRNGDWTFQILVMLEMTPQRGDVYTCHVE 83

                        90
                ....*....|....
gi 24797074 198 HWGLDQPLLKHWEA 211
Cdd:cd21001  84 HPSLQSPITVEWRA 97

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

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 118 PEVTVFPKEPVELGQPNTLICHIDKFFPPVLNVTWLcngeLVTEGVAES-LFLPRTDYSFHKFH---------YLTFVPS 187
Cdd:cd05771   1 PRVRLSPKNLVKPDLPQTLSCHIAGYYPLDVDVEWL----REEPGGSESqVSRDGVSLSSHRQSvdgtysissYLTLEPG 76

                        90       100
                ....*....|....*....|.
gi 24797074 188 AED---FYDCRVEHWGLDQPL 205
Cdd:cd05771  77 TENrgaTYTCRVTHVSLEEPL 97

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

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 115 NDPPE--VTVFPKEPVELgqpnTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFY 192
Cdd:cd21820   3 SDPPKahVTHHPRSEDEV----TLRCWALGFYPADITLTWQLNGEELTQDMELVETRPAGDGTFQKWAAVVVPLGKEQYY 78

                        90
                ....*....|....*...
gi 24797074 193 DCRVEHWGLDQPLLKHWE 210
Cdd:cd21820  79 TCHVYHEGLPEPLTLRWE 96

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 24797074 116 DPPEVTVfPKEPVElGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd21023   4 DPPKAHV-AHHPIS-DHEATLRCWALGFYPAEITLTWQRDGEEQTQDTELVETRPAGDGTFQKWAAVVVPPGEEQRYTCH 81

                        90
                ....*....|....*
gi 24797074 196 VEHWGLDQPLLKHWE 210
Cdd:cd21023  82 VQHEGLPQPLILRWE 96

Class Ia major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen (HLA) H2Db and H2Ld; 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) H2Db and H2Ld. H-2Ld complexed with peptide QL9 (or p2Ca) and complexed with influenza virus peptide NP366-374 (ASNEN-METM), respectively are high-affinity alloantigens for the 2C T cell receptor (TCR). The a1-a2 super domains of H-2Ld, H-2Db, and H-2Kb closely superimpose. 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 24797074 116 DPPE--VTVFPKEPVELgqpnTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYD 193
Cdd:cd21018   4 DSPKahVTHHPRSKGEV----TLRCWALGFYPADITLTWQLNGEELTQDMELVETRPAGDGTFQKWASVVVPLGKEQNYT 79

                        90
                ....*....|....*.
gi 24797074 194 CRVEHWGLDQPLLKHW 209
Cdd:cd21018  80 CRVYHEGLPEPLTLRW 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of T10, T22, and similar proteins; 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 the murine H-2T-encoded T10, T22, and similar proteins. T10 and T22 are highly related nonclassical major histocompatibility complex (MHC) class Ib proteins that bind to certain gammadelta T cell receptors (TCRs) in the absence of other components. Classical MHC class I (class Ia) molecules participate in immune responses by presenting peptide antigens to cytolytic alpha beta T cells. Many nonclassical MHC class I (class Ib) molecules have distinct antigen-binding capabilities, suggesting that they have evolved for specific tasks that are distinct from those of MHC class Ia. Members of the IgC 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, and the IgC domain is involved in oligomerization and molecular interactions.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 115 NDPPE--VTVFPKEPVELgqpnTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFY 192
Cdd:cd21016   3 SDPPKahVTRHPRPEGDV----TLRCWALGFYPADITLTWQKDGEELTQDMEFVETRPAGDGTFQKWAAVVVPLGKEQSY 78

                        90
                ....*....|....*...
gi 24797074 193 DCRVEHWGLDQPLLKHWE 210
Cdd:cd21016  79 TCHVYHEGLPEPLTLRWE 96

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
                ....*....|....*....|....*....|....*....|....*....|
gi 24797074 117 PPEVTVFPKEPVELGQPN--TLICHIDKFFPPVLNVTWLCNGELVTEGVA 164
Cdd:cd05769   2 PPTVALFPPSEAEIRNKRkaTLVCLATGFYPDHVSLSWKVNGKEVKDGVA 51

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        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 116 DPPEVTVFPKEPVElgQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd21020   4 DPPKAHVTHHRRPE--GDVTLRCWALGFYPADITLTWQLNGEELTQEMELVETRPAGDGTFQKWASVVVPLGKEQKYTCH 81

                        90
                ....*....|....
gi 24797074 196 VEHWGLDQPLLKHW 209
Cdd:cd21020  82 VEHEGLPEPLTLRW 95

Class Ib major histocompatibility complex (MHC) immunoglobulin domain of human leukocyte antigen H; 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 H (HLA-H). HLA-H (also known as hereditary hemochromatosis protein; HFE) is a major histocompatibility complex (MHC) class I-like protein that is mutated in Hereditary Hemochromatosis. HFE is a protein of 343 amino acids that includes a signal peptide, an extracellular transferrin receptor-binding region (a1 and a2), an immunoglobulin-like domain (a3), a transmembrane region, and a short cytoplasmic tail. HFE binds beta-2-microglobulin to form a heterodimer expressed at the cell surface. It binds transferrin receptor (TFRC) in its extracellular alpha1-alpha2 domain. HFE plays an important part in the regulation of hepcidin expression in response to iron overload and the liver is important in the pathophysiology of HFE-associated hemochromatosis. Nine HFE splicing variants have been reported with transcripts lacking exon 2 or exon 3, or exons 2-3, 2-4, or 2-5. Diverse mutations involving HFE introns and exons discovered in persons with hemochromatosis or their family members cause or probably cause high iron phenotypes. 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 24797074 135 TLICHIDKFFPPVLNVTWLCNGELVTEGVAESL-FLPRTDYSFHKFHYLTFVPSAEDFYDCRVEHWGLDQPLLKHW 209
Cdd:cd21021  19 TLRCRALNYYPQNITMKWLKDKQPMDAKEFEPKdVLPNGDGTYQGWITLAVPPGEEQRYTCQVEHPGLDQPLIVIW 94

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        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 24797074 116 DPPEVTVfPKEPVeLGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYDCR 195
Cdd:cd21022   3 DPPKTHV-THHPV-FDYEATLRCWALGFYPAEIILTWQRDGEDQTQDVELVETRPAGDGTFQKWAAVVVPSGEEQRYTCH 80

                        90
                ....*....|....
gi 24797074 196 VEHWGLDQPLLKHW 209
Cdd:cd21022  81 VQHEGLPEPLMLRW 94

H-2 class I histocompatibility complex TLA (thymus leukemia antigen); member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the major histocompatibility complex (MHC) H-2 class I histocompatibility complex TLA (thymus leukemia antigen). The murine MHC class I histocompatibility TLA (Thymus leukemia antigen), which is encoded in the T region by T3 and T18 genes, is expressed mainly by intestinal epithelial cells and thymocytes. The murine TLAs are class I, beta-2-microglobulin-associated glycoproteins. The TLA function is not defined by antigen presentation, but rather by its relatively high affinity binding to CD8-alpha-alpha compared with CD8-alpha-beta. The existence of a human homolog for murine TLA remains unresolved. This group is a member of the C1-set Ig domains, which 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 24797074 116 DPPE--VTVFPKEPVELgqpnTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFLPRTDYSFHKFHYLTFVPSAEDFYD 193
Cdd:cd21012   4 DPPKthVTHHPRPEGYV----TLRCWALGFYPAHITLTWQLNGEELIQDTELVETRPAGDGTFQKWAAVVVPSGEEQKYT 79

                        90
                ....*....|....*.
gi 24797074 194 CRVEHWGLDQPLLKHW 209
Cdd:cd21012  80 CHVYHEGLPEPLTLRW 95

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 24797074 117 PP--EVTvfpKEPVELGQPNTLICHIDKFFPPVLNVTWLCNGELVTEGVAESLFL-PRTDYSFHKFHYLTFVPSAEDF-Y 192
Cdd:cd16085   2 PPtlEVT---QQPTMVWNQVNVTCQVEKFYPQRLQLTWLENGNVSRTETPSTLTVnKDGTYNWTSWLLVNVSAHREDVvL 78

                        90
                ....*....|..
gi 24797074 193 DCRVEHWGldQP 204
Cdd:cd16085  79 TCQVEHDG--QP 88

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 24797074 118 PEVTVFPKEPVELGQPNT--LICHIDKFFPPVLNVTWLCNGELVTEGVAES--------LFLPRTDYSFHKFHYLtfvps 187
Cdd:cd05847   1 PTVQILHSSCASTLTSETiqLLCLISGYTPSTIEVEWLVDGQVATLSAASTapqkeeggTFSTTSKLNVTQEDWK----- 75

                        90
                ....*....|....*
gi 24797074 188 AEDFYDCRVEHWGLD 202
Cdd:cd05847  76 SGKTYTCKVTHQGTT 90