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 226823365 111 WLLLQTSADMVLVHGSFDIRCHGWKNWNVRKVIYYRNDHAFNYSYESP-VSIREATLNDSGTYHCKGYLRQVKYESDKFR 189
Cdd:cd05753    1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSnFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                 ...
gi 226823365 190 IAV 192
Cdd:cd05753   81 ITV 83

Second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 226823365 111 WLLLQTSADMVLVHGSFDIRCHGWKNWNVRKVIYYRNDHAFNYSYESP-VSIREATLNDSGTYHCKGYLRQVKYESDKFR 189
Cdd:cd05753    1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSnFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                 ...
gi 226823365 190 IAV 192
Cdd:cd05753   81 ITV 83

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 226823365   29 VLTLDPPWIRIFTGEKVTLSC--YGNNHlqmnSTTKWIHNGTV----------SEVNSSHLVIVSATVQDSGKYICQ 93
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCeaTGSPP----PTITWYKNGEPissgstrsrsLSGSNSTLTISNVTRSDAGTYTCV 75

Second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs), and similar domains; The members here are composed of the second immunoglobulin (Ig)-like domain of Fcgamma-receptors (FcgammaRs). Interactions between IgG and FcgammaR are important to the initiation of cellular and humoral response. IgG binding to FcgammaR leads to a cascade of signals and ultimately to functions such as antibody-dependent-cellular-cytotoxicity (ADCC), endocytosis, phagocytosis, release of inflammatory mediators, etc. FcgammaR has two Ig-like domains. This group also contains FcepsilonRI which binds IgE with high affinity.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 226823365 111 WLLLQTSADMVLVHGSFDIRCHGWKNWNVRKVIYYRNDHAFNYSYESP-VSIREATLNDSGTYHCKGYLRQVKYESDKFR 189
Cdd:cd05753    1 WLLLQAPSAVVFEGEPLTLRCHGWKDKKVHKVTYYKDGKALKFSYENSnFSIPQATLSDSGSYHCSGTVRIKRRSSESVN 80

                 ...
gi 226823365 190 IAV 192
Cdd:cd05753   81 ITV 83

Immunoglobulin domain; This family contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 226823365   29 VLTLDPPWIRIFTGEKVTLSC--YGNNHlqmnSTTKWIHNGTV----------SEVNSSHLVIVSATVQDSGKYICQ 93
Cdd:pfam13927   3 VITVSPSSVTVREGETVTLTCeaTGSPP----PTITWYKNGEPissgstrsrsLSGSNSTLTISNVTRSDAGTYTCV 75

Immunoglobulin domain; This domain contains immunoglobulin-like domains.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 226823365   30 LTLDPPWIRIFTGEKVTLSCYGNNHLQmnSTTKWIHNGTVseVNSSH-LVIVSATVQDSGKYICQ---KQGLFKSKPVYL 105
Cdd:pfam13895   2 PVLTPSPTVVTEGEPVTLTCSAPGNPP--PSYTWYKDGSA--ISSSPnFFTLSVSAEDSGTYTCVarnGRGGKVSNPVEL 77

                  ..
gi 226823365  106 NV 107
Cdd:pfam13895  78 TV 79

Sixth immunoglobulin (Ig) domain of contactin-2; The members here are composed of the sixth immunoglobulin (Ig) domain of the neural cell adhesion molecule contactin-2-like. Contactins are comprised of six Ig domains followed by four fibronectin type III (FnIII) domains anchored to the membrane by glycosylphosphatidylinositol. Contactin-2 (TAG-1, axonin-1) facilitates cell adhesion by homophilic binding between molecules in apposed membranes. It may play a part in the neuronal processes of neurite outgrowth, axon guidance and fasciculation, and neuronal migration. The first four Ig domains form the intermolecular binding fragment, which arranges as a compact U-shaped module by contacts between IG domains 1 and 4, and domains 2 and 3. The different contactins show different expression patterns in the central nervous system. During development and in adulthood, contactin-2 is transiently expressed in subsets of central and peripheral neurons. Contactin-2 is also expressed in retinal amacrine cells (AC) in the developing chick retina, corresponding to the period of formation and maturation of AC processes.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 226823365  30 LTLDPPWIRIFTGEKVTLSCYGNNHLQMNSTTKWIHNGTVSEVNSSH--------------LVIVSATVQDSGKYICQKQ 95
Cdd:cd05854    5 ITLAPSSADINQGENLTLQCHASHDPTMDLTFTWSLDDFPIDLDKPNghyrrmevketigdLVIVNAQLSHAGTYTCTAQ 84

                 ....*
gi 226823365  96 GLFKS 100
Cdd:cd05854   85 TVVDS 89

Third immunoglobulin domain in Cluster of Differentiation (CD) 22; member of the Constant 2 (C2)-set of IgSF domains; The members here are composed of the third immunoglobulin domain in Cluster of Differentiation (CD) 22 (also known as Siglec-2). CD22, a sialic-acid binding immunoglobulin type-lectin (Siglec) family member, is an inhibitory co-receptor of the B-cell receptor (BCR). The inhibitory function of CD22 and its restricted expression on B cells makes CD22 an attractive target against dysregulated B cells that cause autoimmune diseases and B-cell-derived cancers. CD22 plays a vital role in establishing a baseline level of B-cell inhibition, and thus is an important determinant of homeostasis in humoral immunity. Siglecs are primarily expressed on immune cells and recognize sialic acid-containing glycan ligands. Siglecs are 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 (Siglec-4, myelin-associated glycoprotein), the other subgroup is comprised of CD33-related Siglecs which include CD33 (Siglec-3) and human Siglecs 5-11. 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. This group belongs to the C2-set of IgSF domains, having A, B, and E strands in one beta-sheet and A', G, F, C' in the other. Unlike other Ig domain sets, the C2-set lacks the D strand.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 226823365  42 GEKVTLSCYGNNHLQMNSTTKWIHNGT-VSEVNSSHLVIVSATVQDSGKYICQKQ---GLFKSKPVYLNV 107
Cdd:cd20937   17 GDSVTMTCEVSSSNPEYTTVSWLKDGTsLKKQNTFTLNLREVTKDQSGKYCCQVSndvGPGRSEEVFLQV 86