Processing glycosidases of Saccharomyces cerevisiae

The properties of the N-glycan processing glycosidases located in the endoplasmic reticulum of Saccharomyces cerevisiae are described. alpha-Glucosidase I encoded by CWH4I cleaves the terminal alpha 1,2-linked glucose and alpha-glucosidase II encoded by ROT2 removes the two alpha 1,3-linked glucose residues from the Glc(3)Man(9)GlcNAc(2) oligosaccharide precursor while the alpha 1,2-mannosidase encoded by MNS1 removes one specific mannose to form a single isomer of Man(8)GlcNAc(2). Although trimming by these glycosidases is not essential for the formation of N-glycan outer chains, recent studies on mutants lacking these enzymes indicate that alpha-glucosidases I and II play an indirect role in cell wall beta 1,6-glucan formation and that the alpha 1,2-mannosidase is involved in endoplasmic reticulum quality control. Detailed structure-function studies of recombinant yeast alpha 1,2-mannosidase are described that serve as a model for other members of this enzyme family that has been conserved through eukaryotic evolution. (C) 1999 Elsevier Science B.V. All rights reserved.