title: Characterization of lipid-linked octa- through undecasaccharides implicated in the biosynthesis of Saccharomyces cerevisiae mannoproteins.
abstract: The lipid-linked oligosaccharide Glc3-Man9(GlcNAc)2 (Glc, glucose; Man, mannose; GlcNAc, N-acetylglucosamine) serves as a precursor for the biosynthesis of the inner core portion of the asparagine-linked polysaccharide of Saccharomyces cerevisiae mannoproteins. It has been shown previously that incubation of a microsomal preparation from this organism with UDP-N-acetylglucosamine and GDP-[14C]mannose gives rise to a series of lipid-linked oligosaccharides of the general structure Mann(GlcNAc)2, with n from 1 to 9. A structural characterization of Man1- to Man5(GlcNAc)2 oligosaccharides indicated that the major structures among these were identical to the intermediates proposed for the biosynthesis of animal glycoproteins (C. Prakash and I. K. Vijay, Biochemistry 21:4810-4818, 1982). In the present study, the structural characterization of the Man6- through Man9(GlcNAc)2 species was conducted. The Man6- through Man8(GlcNAc)2 species have two isomers, whereas Man9(GlcNAc)2 is monoisomeric. One isomer each of Man6- through Man8(GlcNAc)2 and the monoisomeric Man9(GlcNAc)2 are identical to the intermediates for the biosynthesis of asparagine-linked glycoproteins in animal systems. It is proposed that the steps of the lipid-linked assembly of the carbohydrate precursor for S. cerevisiae mannoproteins are identical to those of the major pathway in animal systems. A lack of acceptor substrate specificity by the mannosyltransferases, as observed with in vitro studies with animal systems, also might be responsible for the biosynthesis of multiple isomers reported here.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D005656:Fungal Proteins / Q000096:biosynthesis*; D006023:Glycoproteins / Q000096:biosynthesis*; D007536:Isomerism; D008070:Lipopolysaccharides / Q000032:analysis* / Q000378:metabolism; D008562:Membrane Glycoproteins; D012441:Saccharomyces cerevisiae / Q000032:analysis* / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D005656:Fungal Proteins; D006023:Glycoproteins; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; C023023:lipid-linked oligosaccharides; C025363:mannoproteins