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Immunoglobulin Variable region-containing chitin-binding proteins; an immunoglobulin V-set domain The members here are composed of the immunoglobulin variable (IgV) region-containing chitin-binding proteins (VCBPs). VCBPs are secreted, immune-type molecules that have been identified in both amphioxus and sea squirt (Ciona intestinalis). VCBPs, which consist of a leader peptide, two tandem N-terminal immunoglobulin V-type domains and a single C-terminal chitin-binding domain, belong to a multigene family encoding secreted proteins. The VCBPs were identified first in the cephalochordate Branchiostoma floridae and show structural similarities with V-type domains of immunoglobulins and T cell receptors, suggesting that VCBPs represent a unique gut-associated form of innate immune proteins. 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, such as, T-cell receptors, CD2, CD4, CD8, and membrane glycoproteins, such as, 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. 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 V-set of IgSF domains, having A, B, E and D strands in one beta-sheet and A', G, F, C, C' and C" in the other. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",