Genetic, biochemical, and morphological evidence for the involvement of N-glycosylation in biosynthesis of the cell wall β1,6-glucan of Saccharomyces cerevisiae

摘要

Recent evidence indicates that Stt3p plays a central role in the recognition and/or catalytic step in N-glycosylation (asparagine-linked glycosylation) in the lumen of the endoplasmic reticulum. It is known that stt3 mutants exhibit certain phenotypic features that are suggestive of a cell wall defect. To understand the basis of these phenotypes, we devised a genetic screen to isolate strains bearing mutations that lead to synthetic lethality in combination with the stt3–1 mutation. Using this screen, we were surprised to identify two KRE genes (KRE5 and KRE9) that are involved in the biosynthesis of the cell wall β1,6-glucan. This finding led us to propose that the N-glycosylation process is essential in the biosynthesis of cell wall β1,6-glucan. This proposal was supported by the observation that several stt3 mutants exhibited a 60–70% reduction in the content of cell wall β1,6-glucan as compared with WT cells. Transmission electron microscopy revealed that the stt3 mutant strains exhibit a diffused cell wall with loss of the outer mannoprotein layer as compared with the WT cells. Thus, we provide genetic, morphological, and biochemical evidence for the critical involvement of N-glycosylation in some step in assembly of the cell wall β1,6-glucan in Saccharomyces cerevisiae.