Individual chitin synthase enzymes synthesize microfibrils of differing structure at specific locations in the Candida albicans cell wall

Abstract

The shape and integrity of fungal cells is dependent on the skeletal polysaccharides in their cell walls of which β(1,3)-glucan and chitin are of principle importance. The human pathogenic fungus Candida albicans has four genes, CHS1, CHS2, CHS3 and CHS8, which encode chitin synthase isoenzymes with different biochemical properties and physiological functions. Analysis of the morphology of chitin in cell wall ghosts revealed two distinct forms of chitin microfibrils: short microcrystalline rodlets that comprised the bulk of the cell wall; and a network of longer interlaced microfibrils in the bud scars and primary septa. Analysis of chitin ghosts of chs mutant strains by shadow-cast transmission electron microscopy showed that the long-chitin microfibrils were absent in chs8 mutants and the short-chitin rodlets were absent in chs3 mutants. The inferred site of chitin microfibril synthesis of these Chs enzymes was corroborated by their localization determined in Chsp–YFP-expressing strains. These results suggest that Chs8p synthesizes the long-chitin microfibrils, and Chs3p synthesizes the short-chitin rodlets at the same cellular location. Therefore the architecture of the chitin skeleton of C. albicans is shaped by the action of more than one chitin synthase at the site of cell wall synthesis.