Molecular and genetic control of chitin biosynthesis in fungi

Chitin is the most important structural component of the cell walls of fungi. Its synthesis involves the transfer of N-acetylglucosaminyl residues from the universal donor UDPGlcNAC to the growing chain. This reaction is catalyzed by an ill-defined enzyme called chitin synthetase. By use of diverse techniques, including reverse genetics, it has been possible to isolate mutants affected in chitin biosynthesis in vitro and in vivo. These studies have permitted the identification of several genes that code for the catalytic components of the enzyme, and probably for ancillary reactions. In general, two types of genes have been identified in fungi. The so-called CHS genes, from which two families, and possibly three classes exist, code for chitin synthetases activated by proteases. All fungi thus far studied contain more than one CHS gene, which are normally dispensable. The second class are larger, essential genes coding for the catalytic polypeptide of chitin synthetases non-activated by proteolysis, and probably made of more than one polypeptide. These are labeled CSD2 or CAL1. It may be hoped that our knowledge of chitin synthetase will make them the most suitable targets for new strategies to control fungal infections.