Immunoglobulin domain; The members here are composed of the immunoglobulin (Ig) domain found in the Ig superfamily. The Ig superfamily is a heterogenous group of proteins, built on a common fold comprised of a sandwich of two beta sheets. Members of this group are components of immunoglobulin, neuroglia, cell surface glycoproteins, including T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, including butyrophilin and chondroitin sulfate proteoglycan core protein. A predominant feature of most Ig domains is a disulfide bridge connecting the two beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E, and D strands in one sheet and A', G, F, C, C' and C" in the other. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other by strands G, F, C, and C'. Moreover, a C1-set Ig domain contains a short C' strand (three residues) and lacks A' and C" strand. Unlike other Ig domain sets, C2-set structures do not have a D strand. Like the V-set Ig domains, members of the I-set have a discontinuous A strand, but lack a C" strand.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   8 SPKPTVFLPSIAKIKLHNAGTYLCLLENFFPNVIKVYWKEKNGNKVLESQQGNTMRTTNTYMKFSWLTVSKTAMDKEHKC 87
Cdd:cd07697     1 SPKPTIFLPSIAETEKQKAGTYLCLLENFFPDVIKIHWREKKSDTILESQEGNTEKTKDTYMKFSWLTVPKKSLGKEHRC 80

                          90
                  ....*....|....*...
gi 1952965047  88 VVKHEKNRGGVDQEIIFP 105
Cdd:cd07697    81 IYKHENNKNGVKQEIIFP 98

T cell receptor (TCR) gamma chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) constant (C) domain of the gamma chain of gamma-delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha-beta TCRs, but a small subset contain gamma-delta TCRs. Alpha-beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma-delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing and MHC independently of the bound peptide. Gamma-delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   8 SPKPTVFLPSIAKIKLHNAGTYLCLLENFFPNVIKVYWKEKNGNKVLESQQGNTMRTTNTYMKFSWLTVSKTAMDKEHKC 87
Cdd:cd07697     1 SPKPTIFLPSIAETEKQKAGTYLCLLENFFPDVIKIHWREKKSDTILESQEGNTEKTKDTYMKFSWLTVPKKSLGKEHRC 80

                          90
                  ....*....|....*...
gi 1952965047  88 VVKHEKNRGGVDQEIIFP 105
Cdd:cd07697    81 IYKHENNKNGVKQEIIFP 98

Immunoglobulin C1-set domain;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047  12 TVFLPSIAKIKLHNagTYLCLLENFFPNVIKVYWKeKNGNKV-------LESQQGNtmrttNTYMKFSWLTVSKTAMD-- 82
Cdd:pfam07654   2 YVFPPSPEELGKPN--TLTCLVTGFYPPDITVTWL-KNGQEVtegvkttPPSPNSD-----WTYQLSSYLTVTPSDWEsg 73

                          90
                  ....*....|
gi 1952965047  83 KEHKCVVKHE 92
Cdd:pfam07654  74 DEYTCRVEHE 83

T cell receptor (TCR) gamma chain constant immunoglobulin domain; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) constant (C) domain of the gamma chain of gamma-delta T-cell receptors (TCRs). TCRs mediate antigen recognition by T lymphocytes and are heterodimers consisting of alpha and beta chains or gamma and delta chains. Each chain contains a variable (V) and a constant (C) region. The majority of T cells contain alpha-beta TCRs, but a small subset contain gamma-delta TCRs. Alpha-beta TCRs recognize antigen as peptide fragments presented by major histocompatibility complex (MHC) molecules. Gamma-delta TCRs recognize intact protein antigens; they recognize protein antigens directly and without antigen processing and MHC independently of the bound peptide. Gamma-delta T cells can also be stimulated by non-peptide antigens such as small phosphate- or amine-containing compounds.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   8 SPKPTVFLPSIAKIKLHNAGTYLCLLENFFPNVIKVYWKEKNGNKVLESQQGNTMRTTNTYMKFSWLTVSKTAMDKEHKC 87
Cdd:cd07697     1 SPKPTIFLPSIAETEKQKAGTYLCLLENFFPDVIKIHWREKKSDTILESQEGNTEKTKDTYMKFSWLTVPKKSLGKEHRC 80

                          90
                  ....*....|....*...
gi 1952965047  88 VVKHEKNRGGVDQEIIFP 105
Cdd:cd07697    81 IYKHENNKNGVKQEIIFP 98

Immunoglobulin Constant-1 (C1)-set domain; The members here are composed of C1-set domains, classical Ig-like domains resembling the antibody constant domain. Members of the IgC1 family are components of immunoglobulin, T-cell receptors, CD1 cell surface glycoproteins, secretory glycoproteins A/C, and major histocompatibility complex (MHC) class I/II molecules. In immunoglobulins, each chain is composed of one variable domain (IgV) and one or more IgC domains. These names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. The IgV domain is responsible for antigen binding, while the IgC domain is involved in oligomerization and molecular interactions. The structures in C1-set are smaller than those in the V-set; they have one beta sheet that is formed by strands A, B, E, and D and the other strands by G, F, C, and C'.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047  10 KPTVFLPSIAKIKLHNAgTYLCLLENFFPNVIKVYWKeKNGNKVLESQQGNT--MRTTNTYMKFSWLTVSKTAMDKEHK- 86
Cdd:cd00098     1 TVTLLPPSPEEKGGGKV-TLVCLVSGFYPKDITVTWL-KNGVPLTSGVSTSSpvEPNDGTYSVTSSLTVPPSDWDEGATy 78

                  ....*..
gi 1952965047  87 -CVVKHE 92
Cdd:cd00098    79 tCVVTHE 85

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

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   9 PKPTVFLPSIAKIKLHNAGTYLCLLENFFPNVIKVYWKeKNGNKVLESQQGN---TMRTTNTYMKFSWLTVSKTAMDKEH 85
Cdd:cd05769     3 PTVALFPPSEAEIRNKRKATLVCLATGFYPDHVSLSWK-VNGKEVKDGVATDpqaLRENTSTYSLSSRLRVSATEWFNPR 81

                          90
                  ....*....|..
gi 1952965047  86 K---CVVKHEKN 94
Cdd:cd05769    82 NtftCIVKFYGG 93

Class II major histocompatibility complex (MHC) alpha chain immunoglobulin domain of histocompatibility antigen (HLA) DQ and related proteins; member of the C1-set of Ig superfamily (IgSF) domains; The members here are composed of the immunoglobulin (Ig) domain of major histocompatibility complex (MHC) class II alpha chain of histocompatibility antigen (HLA) DQ. MHC class II molecules are encoded by three different loci, HLA-DR, -DQ, and -DP, which are about 70% similar to each other. HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an alphabeta heterodimer of type MHC class II. The alpha and beta chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. A person often produces two alpha-chain and two beta chain variants and thus 4 isoforms of DQ. Two autoimmune diseases in which HLA-DQ is involved are celiac disease and diabetes mellitus type 1. DQ is one of several antigens involved in rejection of organ transplants. DQ8 is a split antigen of the DQ3 broad antigen. MHC class II molecules play a key role in the initiation of the antigen-specific immune reponse. These molecules have been shown to be expressed constitutively on the cell surface of professional antigen-presenting cells (APCs), including B-lymphocytes, monocytes, and macrophages in both humans and mice. The expression of these molecules has been shown to be induced in nonprofessional APCs such as keratinocyctes, and they are expressed on the surface of activated human T cells and on T cells from other species. The MHC II molecules present antigenic peptides to CD4(+) T-lymphocytes. These peptides derive mostly from proteolytic processing via the endocytic pathway, of antigens internalized by the APC. These peptides bind to the MHC class II molecules in the endosome before they are transported to the cell surface. MHC class II molecules are heterodimers, comprised of two similarly-sized membrane-spanning chains, alpha and beta. Each chain had two globular domains (N- and C-terminal), and a membrane-anchoring transmembrane segment. The two chains form a compact four-domain structure. The peptide-binding site is a cleft in the structure.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   9 PKPTVFlpSIAKIKLHNAGTYLCLLENFFPNVIKVYWKeKNGNKVLE--SQQGNTMRTTNTYMKFSWLTVSKTAmDKEHK 86
Cdd:cd21008     3 PEVTVF--PKSPVTLGQPNTLICLVDNIFPPVINITWL-SNGHSVTEgvSETSFLSKSDHSFLKISYLTFLPSA-DDIYD 78

                  ....*
gi 1952965047  87 CVVKH 91
Cdd:cd21008    79 CKVEH 83

CH3 domain (third constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, gamma, and delta chains, and CH4 domain (fourth constant Ig domain of the heavy chain) in immunoglobulin heavy alpha, epsilon, and mu chains; member of the C1-set of I; The members here are composed of the third and fourth immunoglobulin constant domain (IgC) of alpha, delta, gamma and alpha, epsilon, and mu heavy chains, respectively. This domain is found on the Fc fragment. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. There are two types of light chains: kappa and lambda; each is composed of a constant domain and a variable domain. There are five types of heavy chains: alpha, delta, epsilon, gamma, and mu, all consisting of a variable domain (VH) with three (alpha, delta and gamma) or four (epsilon and mu) constant domains (CH1 to CH4). Ig molecules are modular proteins, in which the variable and constant domains have clear, conserved sequence patterns.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1952965047   9 PKPTVFLPSIAKIKLHNAGTYLCLLENFFPNVIKVYWKEknGNKVLESQQGNT----MRTTNTYMKFSWLTVSKTAMDKE 84
Cdd:cd05768     1 PSVYLLPPPEEELSLNETVTLTCLVKGFYPEDIFVSWLQ--NGEPLPSADYKTtapvPESDGSFFVYSKLNVSTADWNSG 78

                          90
                  ....*....|
gi 1952965047  85 HK--CVVKHE 92
Cdd:cd05768    79 DVfsCVVGHE 88

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 1952965047  11 PTVFlPSIAKIKLHNAGTYL--CLLENFFPNVIKVYWKEKNGNKVLESQQG--NTMRTTNTYMKFSWLTV-SKTAMDKEH 85
Cdd:cd04985     2 PTVF-PLQSATKSQSNGPVAlgCLISDYFPESITVSWQKNTNSITSGFTRTfpVVLRSGGDYSCSSQLTVpLQEWNSGEV 80

                          90
                  ....*....|....*...
gi 1952965047  86 -KCVVKHEKNRGGVDQEI 102
Cdd:cd04985    81 yKCQVQHSASNSKQEKDV 98