Activation mechanism, functional role and shedding of glycosylphosphatidylinositol‐anchored Yps1p at the Saccharomyces cerevisiae cell surface

Abstract

SummaryYeast cell wall assembly is a highly regulated and dynamic process. A class of cell surface aspartic peptidases anchored by a glycosylphosphatidylinositol (GPI) group, collectively known as yapsins, was proposed to be involved in cell wall construction. The Saccharomyces cerevisiae Yps1p, the prototypal yapsin, is processed internally within a loop region to produce an a/b two-subunit enzyme. Here we investigated the activation mechanism of GPI-anchored Yps1p and identified some of its substrates. We report that all activation steps of GPI-Yps1p take place at the cell surface and are regulated by the environmental pH. GPI-Yps1p is active in vivo at pH 6.0 and pH 3.0 and functions as a sheddase for a subset of GPI-anchored enzymes, including itself and the Gas1 glucanosyltransferase. Importantly, while native GPI-Yps1p weakly suppresses many phenotypes associated with the yeast kex2D mutant, loop mutants that interfere with conversion into the two-subunit enzyme restore the kex2D phenotypes to near wild type level. We propose that cleavage of this internal loop region plays an important regulatory function through stimulating its shedding activity. Collectively, our data provide a direct link between the pH regulation of yeast cell wall assembly and the activity of a yapsin.

Proteolytic Cleavage of Covalently Linked Cell Wall Proteins by Candida albicans Sap9 and Sap10

“…This is similar to S. cerevisiae, as yapsin deletion mutants develop cell wall integrity defects (33) and ScYps1 was shown to cleave the cell wall remodeling CWPs ScPir4 and ScGas1 (20). However, the consequences of proteolytic processing of distinct CWPs for their function remains unclear.…”

“…The near neutral pH optima and activity over a broad pH range distinguishes Sap9 and Sap10 from the other secreted Saps, which exhibit activity at more acidic pH optima and a more narrow pH range. The S. cerevisiae yapsins show similar activity over a broad pH range, depending on the substrate cleaved (20,52), but the significant activity at neutral to basic pH seems to be specific for Sap9 and Sap10. This may reflect the host-associated lifestyle of C. albicans requiring regulatory proteolytic digests at several different host niches with different pH values.…”

Architecture and Biosynthesis of the Saccharomyces cerevisiae Cell Wall

“…These findings suggest that yapsins act on wall hydrolases and transglycosidases, thereby regulating activity of the latter, and hence, incorporation of glucans into the wall (Krysan et al 2005). Support for this came from identification of Gas1, Pir4, and Msb2 as Yps1 substrates (Gagnon-Arsenault et al 2008;Vadaie et al 2008). In addition to degrading or shedding proteins during wall remodeling, yapsins also have roles in mediating release of aberrantly folded or overexpressed GPI proteins that induce ER stress (Miller et al 2010).…”

“…The steps include removal of a propeptide and excision of an internal segment flanked by basic amino acids that separates the enzyme's two catalytic domains, which remain disulfide--linked (Gagnon--Arsenault et al 2006,2008). In the case of Yps1, the propeptide removal and excision steps are likely autocatalytic at an environmental pH of 3, but involve other proteases, including yapsins, at pH 6 (Gagnon-- Arsenault et al 2008).…”

Insight into the Antiadhesive Effect of Yeast Wall Protein 1 of Candida albicans

“…Loss of Ywp1 has no obvious effect on wall resistance properties (23,47), suggesting that Ywp1 does not have a major structural role in the wall. The extensive shedding of Ywp1 and its accumulation in stationary- phase yeast cultures (23) appear to be largely a function of the low pH attained by these cultures and may be mediated by acid hydrolases (17,33). GPI-anchored Sap9 may have a role in this shedding (52; our unpublished observations).…”