AB-INITIO ASSOCIATION WITH BETA(2)-MICROGLOBULIN DURING BIOSYNTHESIS OF THE H-2L(D) CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX HEAVY-CHAIN PROMOTES PROPER DISULFIDE BOND FORMATION AND STABLE PEPTIDE BINDING

In vitro translation studies indicate that the beta(2)-microglobulin ( beta(2)-m) light chain influences the formation of intrachain disulfid e bonds in class I major histocompatibility complex (MHC) molecules du ring their biosynthesis. We now have examined the influence of beta(2) -m on class I MHC intrachain disulfide bond formation in vivo. Using b eta(2)-m(+) and beta(2)-m(-) derivatives of a cell line transfected wi th the mouse H-2L(d) gene, we show that all of the H-2L(d) molecules f rom beta(2)-m(-) cells have both the alpha(2) and alpha(3) intrachain disulfide bonds, whereas about 50% of the H-2L(d) molecules from beta( 2)-m(-) cells have only one of these bonds. All of the free H-2L(d) he avy chains from beta(2)-m(+) cells can undergo a peptide-induced confo rmational change and can bind exogenous peptide and beta(2)-m stably i n vitro. Only those H-2L(d) molecules from beta(2)-m(-) cells, which h ave both intrachain disulfide bonds, undergo a peptide- and beta(2)-m- induced conformational change in vitro. These H-2L(d) molecules do not bind beta(2)-m and peptide stably in vitro. From these results emerge s a greater understanding of the role of beta(2)-m at the time of clas s I MHC molecule synthesis: beta(2)-m promotes intrachain disulfide bo nd formation in the class I MHC molecule and additionally affects clas s I MHC structure to render it competent to form stable trimolecular c omplexes with peptide and beta(2)-m.