Glycoprotein biosynthesis in yeast

Abstract

Many proteins in the yeast Saccharomyces cerevisiae are modified by the attachment of N-linked saccharides to asparagine, of O-linked mannose glycans to serine or threonine, and of glycosylphosphoinositol membrane anchors. The biosynthetic events leading to these modifications are coupled to the secretory pathway. Early stages of N-linked glycosylation and the formation of glycosylphosphoinositol anchors have been conserved through evolution of eukaryotes. Studies of yeast offer a variety of genetic and molecular biological approaches, which have led to the isolation of different glycosylation mutants and of genes for enzymes involved in glycosylation. Yeast mutants are useful to identify biosynthetic intermediates, to establish whether a given enzyme is essential for viability, and to determine how cellular functions are affected when glycosylation is perturbed. Yeast glycosylation mutants and genes can be used to identify their counterparts in other eukaryotes.

Dissecting the role of dolichol in cell wall assembly in the yeast mutants impaired in early glycosylation reactions

“…DolPMan is also a substrate for protein O-mannosylation, where it serves as the donor of the first mannose to be attached to hydroxyl groups of serine and threonine in the protein. The second and subsequent mannose residues are transferred directly from GDPMan (Tanner and Lehle, 1987;Herscovics and Orlean, 1993). Moreover, DolPMan is involved in the synthesis of the sugar part of the glycosyl phosphatidyl inositol anchor in yeast and other eukaryotes (Herscovics and Orlean, 1993).…”

“…The second and subsequent mannose residues are transferred directly from GDPMan (Tanner and Lehle, 1987;Herscovics and Orlean, 1993). Moreover, DolPMan is involved in the synthesis of the sugar part of the glycosyl phosphatidyl inositol anchor in yeast and other eukaryotes (Herscovics and Orlean, 1993). Thus, GDPMan-synthase (Dpm1p) plays a central role in three different pathways (Orlean, 1990).…”

The Ktr1p, Ktr3p, and Kre2p/Mnt1p Mannosyltransferases Participate in the Elaboration of Yeast O- andN-linked Carbohydrate Chains

“…These glycoproteins then proceed through the Golgi complex where their oligosaccharides are further modified. The O-modified proteins of Saccharomyces cerevisiae possess a linear carbohydrate chain of up to 5 mannose residues (1,2). O-Glycosylation is initiated in the ER with dolichyl phosphate-D-mannose as the immediate sugar donor for the mannosyl residue transferred to the hydroxy-amino acids serine and threonine (2,3).…”

“…O-Glycosylation is initiated in the ER with dolichyl phosphate-D-mannose as the immediate sugar donor for the mannosyl residue transferred to the hydroxy-amino acids serine and threonine (2,3). GDP-Man is utilized as the sugar donor in the subsequent elongation of O-linked carbohydrate chains resulting in a linear glycan in which the second and third mannoses possess ␣1,2-linkages, whereas the terminal fourth and fifth mannosyl residues have ␣1,3-linkages (1,2).…”

“…Yeast N-linked modified proteins can acquire two different types of glycan chains after the addition of a Man 8 GlcNAc 2 core in the endoplasmic reticulum, a process common to the majority of eukaryotes (1,2). This primary oligosaccharide can undergo maturation in the Golgi resulting in a Man 8 -13 GlcNAc 2 carbohydrate structure, or it may be extended by an outer chain of variable size (up to 200 mannose residues) that is made up of a backbone of ␣1,6-mannosyl residues to which are attached branched ␣1,2-and ␣1,3-mannosyl side chains.…”