Independent regulation of chitin synthase and chitinase activity in Candida albicans and Saccharomyces cerevisiae

Abstract

Chitin is an essential structural polysaccharide in fungi that is required for cell shape and morphogenesis. One model for wall synthesis at the growing cell surface suggests that the compliance that is necessary for turgor-driven expansion of the cell wall involves a delicate balance of wall synthesis and lysis. Accordingly,de novochitin synthesis may involve coordinated regulation of members of theCHSchitin synthase andCHTchitinase gene families. To test this hypothesis, the chitin synthase and chitinase activities of cell-free extracts were measured, as well as the chitin content of cell walls isolated from isogenic mutant strains that contained single or multiple knock-outs in members of these two gene families, in bothCandida albicansandSaccharomyces cerevisiae. However, deletion of chitinase genes did not markedly affect specific chitin synthase activity, and deletion of singleCHSgenes had little effect onin vitrospecific chitinase activity in either fungus. Chitin synthesis and chitinase production was, however, regulated inC. albicansduring yeast–hypha morphogenesis. InC. albicans, the total specific activities of both chitin synthase and chitinase were higher in the hyphal form, which was attributable mainly to the activities of Chs2 and Cht3, respectively. It appeared, therefore, that chitin synthesis and hydrolysis were not coupled, but that both were regulated during yeast–hypha morphogenesis inC. albicans.