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 85701576  40 FGVNQPERCSGVQGGSIDIPFSFYFPWKLAKDPQMSIAWrwkdFFGH--------FIYNSSMPFIHEHFKGRLILNWTQG 111
Cdd:cd05712   1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYWVSNPVHGYW----YRGGpypkyrppVATNNRTREVHESTQGRFRLLGDPG 76

                        90       100
                ....*....|....*....|...
gi 85701576 112 QTSGVLRILNFKESDQTWYFCRV 134
Cdd:cd05712  77 KKNCSLSISDARPEDSGKYFFRV 99

Immunoglobulin Variable (IgV) domain at the N-terminus of CD33 and related Siglecs (sialic acid-binding Ig-like lectins); The members here are composed of the immunoglobulin (Ig) domain at the N-terminus of Cluster of Differentiation (CD) 33 and related Siglecs (sialic acid-binding Ig-like lectins). Siglec refers to a structurally related protein family that specifically recognizes sialic acid in oligosaccharide chains of glycoproteins and glycolipids. Siglecs are type I transmembrane proteins, organized as an extracellular module composed of Ig-like domains, an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains, followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG, the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 85701576  40 FGVNQPERCSGVQGGSIDIPFSFYFPWKLAKDPQMSIAWrwkdFFGH--------FIYNSSMPFIHEHFKGRLILNWTQG 111
Cdd:cd05712   1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYWVSNPVHGYW----YRGGpypkyrppVATNNRTREVHESTQGRFRLLGDPG 76

                        90       100
                ....*....|....*....|...
gi 85701576 112 QTSGVLRILNFKESDQTWYFCRV 134
Cdd:cd05712  77 KKNCSLSISDARPEDSGKYFFRV 99

Immunoglobulin Variable (IgV) domain at the N-terminus of CD33 and related Siglecs (sialic acid-binding Ig-like lectins); The members here are composed of the immunoglobulin (Ig) domain at the N-terminus of Cluster of Differentiation (CD) 33 and related Siglecs (sialic acid-binding Ig-like lectins). Siglec refers to a structurally related protein family that specifically recognizes sialic acid in oligosaccharide chains of glycoproteins and glycolipids. Siglecs are type I transmembrane proteins, organized as an extracellular module composed of Ig-like domains, an N-terminal variable set of Ig-like carbohydrate recognition domains, and 1 to 16 constant Ig-like domains, followed by transmembrane and short cytoplasmic domains. Human Siglecs are classified into two subgroups, one subgroup is comprised of sialoadhesin (Siglec-1), CD22 (Siglec-2), and MAG, the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11.

                        10        20        30        40        50        60        70        80
                ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 85701576  40 FGVNQPERCSGVQGGSIDIPFSFYFPWKLAKDPQMSIAWrwkdFFGH--------FIYNSSMPFIHEHFKGRLILNWTQG 111
Cdd:cd05712   1 WGLQMPKSVTVQEGLCVLIPCSFSYPADYWVSNPVHGYW----YRGGpypkyrppVATNNRTREVHESTQGRFRLLGDPG 76

                        90       100
                ....*....|....*....|...
gi 85701576 112 QTSGVLRILNFKESDQTWYFCRV 134
Cdd:cd05712  77 KKNCSLSISDARPEDSGKYFFRV 99