GlycoProtein biosynthesis in yeast. protein conformation affects processing of high mannose oligosaccharides on carboxypeptidase Y and invertase.

Carboxypeptidase Y and invertase from baker’s yeast, Saccharomyces cerevisiae, have two classes of Nlinked high mannose oligosaccharides which may be distinguished on the basis of their susceptibility to hydrolysis by endo-8-N-acetylglucosaminidase H (Endo H). Thus, three of the four oligosaccharides on carboxypeptidase Y and seven of nine of those on invertase are readily released by Endo H when these proteins are in their native state (accessible), while the fourth chain on carboxypeptidase Y and the remaining two on invertase are hydrolyzed by Endo H only when these proteins are denatured (inaccessible). Analysis of the three accessible oligosaccharides from carboxypeptidase Y revealed these to be mostly Manll_lnGlcNAc in size and to account for 80% of the mannose and essentially all of the phosphate associated with this enzyme. By contrast, the fourth chain from carboxypeptidase Y ranged in size from Man8-lzGlcNAc and contained no phosphate. Comparison of peptide maps with the primary sequence of carboxypeptidase Y (Svendsen, I., Martin, B. M., Viswanatha, T., and Johansen, J. T. (1982) Carlsberg Res. Cornnun 47, 15-27) allowed assignment of the resistant fourth oligosaccharide to the N-glycosylation sequon located at Asn8.l. A similar analysis of the accessible oligosaccharide pool from invertase showed that all of the phosphate and over 85% of the mannose was in species larger than ManzoGlcNAc, but the oligosaccharides released after denaturation ranged in size from Man8-12GlcNAc and were devoid of phosphate. The smaller size and lack of peripheral modification found on the oligosaccharides that are initially resistant to Endo H is most easily explained by the hypothesis that as carboxypeptidase Y and invertase fold into their mature configuration, certain glycosylated domains become inaccessible to the mannosyl transferases which catalyze chain extension and phosphomannose addition.