Protein glycosylation through dolichol derivatives in baker's yeast

Dolichol-bound sugars are intermediates in the glycosylation of proteins [l-3] . Incubation of liver microsomes with UDP-Glc and Dol-P leads to the synthesis of Dol-P-Glc which in turn may transfer its glucosyl residue to an endogenous acceptor. The glucosylated endogenous acceptor (GEA) is a Dol-PP derivative containing two GlcNAc and probably twelve Man and four Glc residues [4-61. The synthesis of GEA has been detected in microsomes of rat brain, kidney and liver, pig liver, human lymphocytes and hen oviduct ([5] and H. Carminatti, personal communication). The synthesis of Dol-P-Man and of derivatives containing variable amounts of Man residues joined to N’N-diacetylchitobiosyl dolichol pyrophosphate has been found to occur in the microsomes of several animal cells and in plants [2,7,8]. While upon mild acid hydrolysis these derivatives give a series of oligosaccharides due to the different number of Man residues, the glucosyl derivative contains apparently only one oligosaccharide of defined composition. The transfer of the hydrophilic moieties of GEA and of the Dol-PP derivatives containing GlcZVAc and Man residues to endoge:!ous proteins has been detected in animal cell microsomes [7,9-l 11. The glycoproteins thus