| Popis: |
The immunoglobulin superfamily (IgSF) is a large and highly diverse assemblage of related proteins that regulate many different biological processes. The name of the family is based on early studies demonstrating sequence similarity between the antibody (immunoglobulin) variable and constant domains, showing an ancestral link, and the subsequent identification of proteins with similar sequences, suggesting broad diversification and evolution (Williams and Barclay, Annu Rev Immunol 6: 381–405, 1988). Antibodies, the T cell receptors (TCR), and the major histocompatibility complex (MHC), among others, are made up of multiple Ig domain chains that assemble to form the final protein, facilitating antigen presentation/recognition (Fig. 2.1a). The individual Ig domains within this family contain a conserved intra-chain disulfide bond that serves to stabilize the domain. These individual structural domains consist of two “sheets” that consist of beta-strands, as illustrated for a generic Ig-domain (Fig. 2.1b). Many IgSF proteins consist of single chains that string together one or more Ig-domains, each with its own intrinsic features. IgSF proteins can have from one to many such domains, and these are characterized as variable (V) domains, as in Fig. 2.1b, or constant (C) domains based on sequence and structural similarity to the domains characterized in antibodies (Fig. 2.1a). Beyond the conserved core motifs, the family has diverged drastically, and many unique and unusual structural features have evolved. |
