Beta 2-microglobulin induces intracellular transport of human class I transplantation antigen heavy chains in Xenopus laevis oocytes.

Abstract

Human class I transplantation antigens are cell-surface-expressed molecules composed of 1 glycosylated, membrane-integrated H chain and 1 nonglycosylated, water-soluble subunit, .beta.2-microgolbulin (.beta.2m). The intracellular transport of the 2 subunits was examimed by microinjecting mRNA into X. laevis oocytes. .beta.2m, translated in oocytes, was transported and secreted into the medium in the absence of H chains whereas H chains were retained in the endoplasmic reticulum if not cotranslated with .beta.2m. In the presence of .beta.2m, H chains resisted digestion by endoglycosidase H (Endo H), suggesting that .beta.2m promotes the transport of H chains from endoplasmic reticulum to the Golgi compartment. Pulse-chase experiments confirmed this notion. H chains aggregate irreversibly when synthesized in the absence of .beta.2m was ruled out and it is demonstrated that performed H chains will become transported once .beta.2m is available. Intracellular transport is probably controlled by structural features that are part of the transported polypeptide. If so, .beta.2m but not H chains may possess such features.