Synthesis of Glucosyl-Dolichol Derivatives in Bakers' Yeast and Their Role in Protein Glycosylation

Abstract

Two substances soluble in organic solvents were synthesized when UDP-[14C]glucose was incubated with a bakers' yeast particulate fraction. One of them was identified as dolichol-P-glucose by several analytical criteria. The only difference that could be found between the yeast and liver dolichol-P-glucose was the molecular size of their dolichol moieties. According to the molecular weight of the sodium deoxycholate inclusion compounds measured by gel filtration, yeast dolichol-P-glucose contained 15–16 isoprene units. This is in accordance with the known structure of yeast dolichol. The other product soluble in organic solvents was identified as steryl glucoside. Incubation of dolichol-P-[14C]glucose with the yeast particulate fraction led to the transfer of glucose residues to an endogenous acceptor. From evidence gathered in experiments performed with the labelled compound it is suggested that as in animal tissues the glucosylated endogenous acceptor contains two N-acetylhexosamine (possibly N-acetylglucosamine) and several mannose and glucose residues joined to yeast dolichol through a pyrophosphate bridge. Glycosylation of endogenous proteins was detected when a similar glucosylated endogenous acceptor from rat liver was incubated with the yeast particulate fraction. It is suggested that the following reactions of glucose transfer take place in a yeast particulate fraction: Dolichol-P+UDP-glucose Dolichol-P-glucose + UDP Dolichol-P-glucose + Dolichol-P-P-(N-acetylglucosamine)2 (mannose)x Dolichol-P-P-(N-acetylglucosamine)2 (mannose)x (glucose)y+ Dolichol-P Dolichol-P-P-(N-acetylglucosamine)2 (mannose)x (glucose)y+ protein Protein-(N-acetylglucosamine)2 (mannose)x (glucose)y+ Dolichol-P-P.