Lack of the evidence for the enzymatic catabolism of Man1GlcNAc2 in Saccharomyces cerevisiae

In the cytosol of Saccharomyces cerevisiae, most of the free N-glycans (FNGs) are generated from misfolded glycoproteins by the action of the cytoplasmic peptide: N-glycanase (Png1). A cytosol/vacuole -mannosidase, Ams1, then trims the FNGs to eventually form a trisaccharide composed of Man1,4GlcNAc 1,4GlcNAc (Man(1)GlcNAc(2)). Whether or not the resulting Man(1)GlcNAc(2) is enzymatically degraded further, however, is currently unknown. The objective of this study was to unveil the fate of Man(1)GlcNAc(2) in S. cerevisiae. Quantitative analyses of the FNGs revealed a steady increase in the amount of Man(1)GlcNAc(2) produced in the post-diauxic and stationary phases, suggesting that this trisaccharide is not catabolized during this period. Inoculation of the stationary phase cells into fresh medium resulted in a reduction in the levels of Man(1)GlcNAc(2). However, this reduction was caused by its dilution due to cell division in the fresh medium. Our results thus indicate that Man(1)GlcNAc(2) is not enzymatically catabolized in S. cerevisiae.