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.

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                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10946762  30 EGENLTLTCPYNiMLYSLSLKAWQRVRSHGsPETLVLTNtrkadfNVARAGKYLLEDYPTESVVKVTVTGLQRQDVGLYQ 109
Cdd:cd05716  11 EGGSVTIQCPYP-PKYASSRKYWCKWGSEG-CQTLVSSE------GVVPGGRISLTDDPDNGVFTVTLNQLRKEDAGWYW 82

                ....*....
gi 10946762 110 CVVYLSPDN 118
Cdd:cd05716  83 CGVGDDGDR 91

Immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins. pIgR delivers dimeric IgA and pentameric IgM to mucosal secretions. Polymeric immunoglobulin (pIgs) are the first defense against pathogens and toxins. IgA and IgM can form polymers via an 18-residue extension at their C-termini referred to as the tailpiece. pIgR transports pIgs across mucosal epithelia into mucosal secretions. Human pIgR is a glycosylated type I transmembrane protein, comprised of a 620-residue extracellular region, a 23-residue transmembrane region, and a 103-residue cytoplasmic tail. The extracellular region contains five domains that share sequence similarity with Ig variable (v) regions. This group also contains the Ig-like extracellular domains of other receptors such as NK cell receptor Nkp44 and myeloid receptors, among others.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10946762  30 EGENLTLTCPYNiMLYSLSLKAWQRVRSHGsPETLVLTNtrkadfNVARAGKYLLEDYPTESVVKVTVTGLQRQDVGLYQ 109
Cdd:cd05716  11 EGGSVTIQCPYP-PKYASSRKYWCKWGSEG-CQTLVSSE------GVVPGGRISLTDDPDNGVFTVTLNQLRKEDAGWYW 82

                ....*....
gi 10946762 110 CVVYLSPDN 118
Cdd:cd05716  83 CGVGDDGDR 91

Immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins; The members here are composed of the immunoglobulin (Ig)-like domain in the polymeric Ig receptor (pIgR) and similar proteins. pIgR delivers dimeric IgA and pentameric IgM to mucosal secretions. Polymeric immunoglobulin (pIgs) are the first defense against pathogens and toxins. IgA and IgM can form polymers via an 18-residue extension at their C-termini referred to as the tailpiece. pIgR transports pIgs across mucosal epithelia into mucosal secretions. Human pIgR is a glycosylated type I transmembrane protein, comprised of a 620-residue extracellular region, a 23-residue transmembrane region, and a 103-residue cytoplasmic tail. The extracellular region contains five domains that share sequence similarity with Ig variable (v) regions. This group also contains the Ig-like extracellular domains of other receptors such as NK cell receptor Nkp44 and myeloid receptors, among others.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10946762  30 EGENLTLTCPYNiMLYSLSLKAWQRVRSHGsPETLVLTNtrkadfNVARAGKYLLEDYPTESVVKVTVTGLQRQDVGLYQ 109
Cdd:cd05716  11 EGGSVTIQCPYP-PKYASSRKYWCKWGSEG-CQTLVSSE------GVVPGGRISLTDDPDNGVFTVTLNQLRKEDAGWYW 82

                ....*....
gi 10946762 110 CVVYLSPDN 118
Cdd:cd05716  83 CGVGDDGDR 91

Immunoglobulin variable domain (IgV); The members here are composed of the immunoglobulin variable domain (IgV). The IgV family contains the standard Ig superfamily V-set AGFCC'C"/DEB domain topology, and are components of immunoglobulin (Ig) and T cell receptors. The basic structure of Ig molecules is a tetramer of two light chains and two heavy chains linked by disulfide bonds. In Ig, each chain is composed of one variable domain (IgV) and one or more constant domains (IgC); these names reflect the fact that the variability in sequences is higher in the variable domain than in the constant domain. Within the variable domain, there are regions of even more variability called the hypervariable or complementarity-determining regions (CDRs) which are responsible for antigen binding. A predominant feature of most Ig domains is the disulfide bridge connecting 2 beta-sheets with a tryptophan residue packed against the disulfide bond. Ig superfamily (IgSF) domains can be divided into 4 main classes based on their structures and sequences: the Variable (V), Constant 1 (C1), Constant 2 (C2), and Intermediate (I) sets. Typically, the V-set domains have A, B, E and, D strands in one sheet and A', G, F, C, C', and C" strands in the other.

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                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 10946762  30 EGENLTLTCPYN--IMLYSLSlkaWQRVRSHGSPETLVLTNTRKADFNVARAGKYLLEDYPTESVVkVTVTGLQRQDVGL 107
Cdd:cd00099  12 EGESVTLSCEVSssFSSTYIY---WYRQKPGQGPEFLIYLSSSKGKTKGGVPGRFSGSRDGTSSFS-LTISNLQPEDSGT 87

                        90
                ....*....|...
gi 10946762 108 YQCVVYLSPDNVI 120
Cdd:cd00099  88 YYCAVSESGGTDK 100