VPREB1


Immunoglobulin iota chain is a protein that in humans is encoded by the VPREB1 gene. VPREB1 has also recently been designated CD179A.

Function

CD179a is a 126 aa-long polypeptide with apparent MW of 16-18 kDa. It is expressed selectively at the early stages of B cell development, namely, in proB and early preB cells. CD179a has an Ig V domain-like structure, but lacks the last beta-strand of a typical V domain. Instead, it has a carboxyl terminal end that shows no sequence homologies to any other proteins. CD179a associates non-covalently with CD179b carrying an Ig C domain-like structure to form an Ig light chain-like structure, which is called the surrogate light chain or pseudo light chain. In this complex, the incomplete V domain of CD179a appears to be complemented by the extra beta7 strand of CD179b. On the surface of early preB cells, CD179a/CD179b surrogate light chain is disulfide-linked to membrane-bound Ig mu heavy chain in association with a signal transducer CD79a/CD79b heterodimer to form a B cell receptor-like structure, so-called preB cell receptor cellular proliferation, differentiation from the proB cell to preB cell stage, 2) allelic exclusion at the Ig heavy chain gene locus, and 3) promotion of Ig light chain gene rearrangements. Thus, preBCR functions as a checkpoint in early B cell development to monitor the production of Ig mu heavy chain through a functional rearrangement of Ig heavy chain gene as well as the potency of Ig mu heavy chain to associate with Ig light chain.