Cell-surface expression of H-2Db requires N-linked glycans

The question of whether beta-2 microglobulin (B2m)-independent expression of the mouse major histocompatibility complex (MHC) antigen H-2D^b results from the atypical glycosylation pattern associated with this MHC antigen (i. e., three glycans instead of two) has been addressed. Cell-surface expression of transfected H-2D^b in the B2m deficient cell line RIE was completely abolished by the drug tunicamycin (Tm). Introduction of a functional B2m gene by transfection did not re-establish cell-surface expression of D^b in the presence of Tm. Tm had no effect, however, on the expression of a truncated D^b molecule lacking the 1 and 2 domains which is glycosylated at amino acid position 256, suggesting that the D^b molecule, unlike other class I antigens, possesses an unstable conformation in the 1 and/or 2 domains which requires the attachment of glycans before it is transported to the cell surface. Once attached, however, glycans may confer a stable 1/2 conformation apparently peculiar to D^b which allows cell-surface expression in the absence of B2m.