CPS1 , a Homolog of the Streptococcus pneumoniae Type 3 Polysaccharide Synthase Gene, Is Important for the Pathobiology of Cryptococcus neoformans

The polysaccharide capsule is known to be the major factor required for the virulence ofCryptococcus neoformans . We have cloned and characterized a gene, designatedCPS1 , that encodes a protein containing a glycosyltransferase moiety and shares similarity with the type 3 polysaccharide synthase encoded by thecap3B gene ofStreptococcus pneumoniae . Cps1p also shares similarity with hyaluronan synthase of higher eukaryotes. Deletion of theCPS1 gene from a serotype D strain ofC. neoformans resulted in a slight reduction of the capsule size as observed by using an India ink preparation. The growth at 37°C was impaired, and the ability to associate with human brain endothelial cells in vitro was also significantly reduced by the deletion ofCPS1 . Using site-specific mutagenesis, we showed that the conserved glycosyltransferase domains are critical for the ability of the strain to grow at elevated temperatures. A hyaluronan enzyme-linked immunosorbent assay method demonstrated thatCPS1 is important for the synthesis of hyaluronan or its related polysaccharides inC. neoformans . Comparisons between the wild-type and thecps1Δ strains, using three different transmission electron microscopic methods, indicated that theCPS1 gene product is involved in the composition or maintenance of an electron-dense layer between the outer cell wall and the capsule. These and the virulence studies in a mouse model suggested that theCPS1 gene is important in the pathobiology ofC. neoformans .