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

Abstract

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 α-mannosidase, Ams1, then trims the FNGs to eventually form a trisaccharide composed of Manβ1,4GlcNAc β1,4GlcNAc (Man₁GlcNAc₂). Whether or not the resulting Man₁GlcNAc₂ is enzymatically degraded further, however, is currently unknown. The objective of this study was to unveil the fate of Man₁GlcNAc₂ in S. cerevisiae. Quantitative analyses of the FNGs revealed a steady increase in the amount of Man₁GlcNAc₂ 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 Man₁GlcNAc₂. However, this reduction was caused by its dilution due to cell division in the fresh medium. Our results thus indicate that Man₁GlcNAc₂ is not enzymatically catabolized in S. cerevisiae.

Graphical abstract

Man₁GlcNAc₂ is the final enzymatic product of free N-glycan catabolism in S. cerevisiae

Key words:

• free N-glycan
• Saccharomyces cerevisiae
• Man₁GlcNAc₂
• catabolism

Acknowledgments

We thank the members of Glycometabolome team for fruitful discussions.

Notes

Abbreviations: FNG, free N-glycan; STL, stationary phase day-7 to log phase; 2-AP, 2-aminopyridine; HPLC, high-performance liquid chromatography; GU, glucose unit.