Characterisation of a short, glycosylated peptide from yeast; Seripauperin 5 (#273)
Proteins secreted by yeast during fermentation can affect beer and wine production and quality. Gushing, an excess release of foam when a drink is opened, is a key problem for breweries and wineries. Secreted glycoproteins produced by brewing yeast during fermentation have been reported to reduce gushing, particularly the small, highly O-glycosylated seripauperins. Seripauperins stabilise foam in beer and wine production, and are induced by various stress conditions, particularly oxygen and temperature stress. The biological role of seripauperins is unknown. Here we use glyco/proteomics to show how expression and glycosylation of seripauperins differs between yeast strains. The amino acid and DNA sequence conservation of seripauperins implies functional redundancy. Based on amino acid sequences conservation, seripauperins can be grouped into two groups. These groups could be the result of a gene duplication event before the divergence of some strains, as strains seem to favour one group over the other. Seripauperins appear to have varying levels of O-glycosylation, which may allow for functional flexibility. One seripauperin, PAU5, showed high abundance in select yeast strains. This seripauperin was also the only one that could be identified specifically by MS, as it was the only one that had unique MS ion fragments. The predicted structure and glycosylation sites of PAU5, and its conservation with anaerobically-induced cell wall mannoproteins (anCWMPs) such as TIR3 and DAN1, imply a conserved function. The absence of PAU5 did not influence the global proteome of yeast under oxidative or temperature stress, implying a functional redundancy among the highly conserved seripauperins. The glycosylation profiles of individual tryptic fragments from purified PAU5 were unaffected by oxidative stress. Our results will advise selection of yeast strains and growth conditions to control seripauperin glycosylation and abundance in order to modulate foam stability and formation in fermented beverages.