Analysis of beta-glucans and chitin in a Saccharomyces cerevisiae cell wall mutant using high-performance liquid chromatography.

We have previously shown that mutations in the yeast KNR4 gene resulted in pleiotropic cell wall defects, including resistance to killer 9 toxin, elevated osmotic sensitivity to SDS and increased resistance to zymolyase, a (1-->3)-beta-glucanase. In this report, we further demonstrated that knr4 mutant cells were more permeable to a chromogenic substrate, X-GAL, suggesting that the mutant cell walls were leakier to certain non-permeable molecules. To determine if these defects resulted from structural changes in the cell walls, we analysed the alkali-insoluble cell wall components using HPLC assays developed for this purpose. Comparative analysis using four isogenic strains from a 'knr4 disrupted' tetrad demonstrated that mutant cell walls contained much less (1-->3)-beta-glucan and (1-->6)-beta-glucan; however, the level of chitin, a minor cell wall component, was found to be five times higher in the mutant strains compared to the wild-type strains. The data suggested that the knr4 mutant cell walls were dramatically weakened, which may explain the pleiotropic cell wall defects.