CARBOHYDRATES AS STRUCTURAL CONSTITUENTS OF YEAST-CELL WALL AND SEPTUM

The cell walls and septa of fungi are useful models for morphogenesis and potential targets for antifungal agents. In the yeast, Saccharomyces cerevisiae, the main structural components of the primary septum and of the cell wall are chitin and beta(1-->3)glucan, respectively. Two chitin synthetases have been identified in yeast, one of which is essential for septum formation, whereas the other one has a repair function. Both synthetases are bound to the plasma membrane and are found in extracts in a zymogenic form that can be activated by proteases. beta(1-->3)glucan synthetase is also attached to the plasma membrane. Its activity is strongly stimulated by GTP and its analogs. By sequential extraction of the membranes, two components have been obtained in soluble form. One contains a GTP-binding protein; the other probably includes the substrate-binding site. Both components, in addition to GTP, are required for glucan synthesis.