Chitin synthase 1, an auxiliary enzyme for chitin synthesis in Saccharomyces cerevisiae.

Abstract

Abstract. Previously, we showed that chitin synthase 2 (Chs2) is required for septum formation in Saccharomyces cerevisiae, whereas chitin synthase 1 (Chsl) does not appear to be an essential enzyme.However, in strains carrying a disrupted CHS1 gene, frequent lysis of buds is observed. Lysis occurs after nuclear separation and appearg to result from damage to the cell wall, as indicated by osmotic stabilization and by a '~50-nm orifice at the center of the birth scar. Lysis occurs at a low pH and is prevented by buffering the medium above pH 5. A likely candidate for the lytic system is a previously described chitinase that is probably involved in cell separation. The chitinase has a very acidic pH optimum and a location in the periplasmic space that exposes it to external pH. Accordingly, allosamidin, a specific chitinase inhibitor, substantially reduced the number of lysed cells. Because the presence of Chsl in the cell abolishes lysis, it is concluded that damage to the cell wall is caused by excessive chitinase activity at acidic pH, which can normally be repaired through chitin synthesis by Chsl. The latter emerges as an auxiliary or emergency enzyme. Other experiments suggest that both Chsl and Chs2 collaborate in the repair synthesis of chitin, whereas Chsl cannot substitute for Chs2 in septum formation.

WdChs1p, a class II chitin synthase, is more responsible than WdChs2p (Class I) for normal yeast reproductive growth in the polymorphic, pathogenic fungus Wangiella (Exophiala) dermatitidis

“…In addition, disruption of WdCHS1, as in the manner of disruption of CHS2 in S. cerevisiae or lack of expression of CaCHS1 in C. albicans, produces mutants having little reduction in total chitin synthase activity. In contrast, total chitin synthase activity is drastically reduced in strains of the same three species devoid of their functional class I isozymes (Cabib et al 1989;Gow et al 1994;Wang et al 2001). Furthermore, and also in the manner of chs2 disruption mutants of S. cerevisiae and the lack of expression of CaChs1p in conditional mutants of C. albicans (Munro et al 2001;Shaw et al 1991;Schmidt et al 2002), wdchs1Δ cells are occasionally larger and frequently show septal region abnormalities that are not found in mutants with a defective class I isozyme or the wild type, such as failing to separate, showing septa that lack clearly defined primary and secondary septa that are reminiscent of those observed in TEM profiles of W. dermatitidis treated with the chitin synthase inhibitor polyoxin (Cooper et al 1984) and sometimes having abnormally broad mother cell-daughter bud necks and not forming even a defective septum between daughter nuclei.…”

Chitinase and chitin synthase 1: counterbalancing activities in cell separation of Saccharomyces cerevisiae

“…In contrast, null mutations in the structural gene for Chsl did not affect cell division (Bulawa et al, 1986). A defect was, however, observed in strains carrying such mutations : lysis, mostly restricted to daughter cells, occurred when the strains were grown in a medium that allowed acidification to take place during growth (Bulawa et al, 1986;Cabib et al, 1989).…”

“…An analysis of the conditions that favour lysis in chsl NJ 08543-0400, USA. cells led to the hypothesis that excessive chitinase action may be involved in the lytic process (Cabib et al, 1989), which results in perforation of the daughter cell wall during cytokinesis. This idea was supported by the finding that allosamidin, a specific chitinase inhibitor, decreased lysis (Cabib et al, 1989).…”

“…An analysis of the conditions that favour lysis in chsl NJ 08543-0400, USA. cells led to the hypothesis that excessive chitinase action may be involved in the lytic process (Cabib et al, 1989), which results in perforation of the daughter cell wall during cytokinesis. This idea was supported by the finding that allosamidin, a specific chitinase inhibitor, decreased lysis (Cabib et al, 1989). Since cells endowed with Chsl activity do not show lysis even under acidic conditions, it was proposed that Chsl acts as a repair enzyme, by replenishing part of the chitin lost by chitinase digestion (Cabib et al, 1989).…”

Compounds active against cell walls of medically important fungi

“…Elucidation of the factors governing the regulation of chitin synthesis in S. cerevisiae has been the subject of intense research efforts over the past two decades, with a molecular approach providing clarification of many of the previously unresolved issues. To date, several genes regulating different aspects of chitin synthesis in this yeast have been described, CHSI, CHS2, CS02, CS03, CS04, and CALI (32,38,51,220,254). Each has been found to regulate different aspects of chitin synthesis during the growth, budding, and repair of the cell wall of this yeast, with differential levels of activity.…”