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Low environmental pH strongly affected the organization of the Saccharomyces cerevisiae cell wall, resulting in rapidly induced resistance to beta1,3-glucanase. At a molecular level, we found that a considerable amount of Cwp1p became anchored through a novel type of linkage for glycosylphosphatidylinositol (GPI)-dependent cell wall proteins, namely an alkali-labile linkage to beta1,3-glucan. This novel type of modification for Cwp1p did not require the presence of a GPI-derived structure connecting the protein with beta1,6-glucan. In addition, we found high levels of Cwp1p, which was double-anchored through both the novel alkali-sensitive bond to beta1,3-glucan and the alkali-resistant GPI-derived linkage to beta1,6-glucan. Further cell wall analyses demonstrated that Pir2p/Hsp150 and possibly other Pir cell wall proteins, which were already known to be linked to the beta1,3-glucan framework by an alkali-sensitive linkage, were also more efficiently retained in the cell wall at pH 3.5 than at pH 5.5. Consequently, the alkali-sensitive type of linkage of cell wall proteins to beta1,3-glucan was induced by low pH. The low pH-induced alterations in yeast cell wall architecture were demonstrated to be dependent on a functional HOG1 gene, but not on the Slt2p-mediated MAP kinase pathway. Consistent with this observation, DNA microarray studies revealed transcriptional induction of many known high-osmolarity glycerol (HOG) pathway-dependent genes, including four cell wall-related genes, namely CWP1, HOR7, SPI1 and YGP1.
Kapteyn et al. (Mon,) studied this question.