title: Cryptococcal xylosyltransferase 1 (Cxt1p) from Cryptococcus neoformans plays a direct role in the synthesis of capsule polysaccharides.
abstract: The opportunistic yeast Cryptococcus neoformans causes serious disease in humans and expresses a prominent polysaccharide capsule that is required for its virulence. Little is known about how this capsule is synthesized. We previously identified a beta1,2-xylosyltransferase (Cxt1p) with in vitro enzymatic activity appropriate for involvement in capsule synthesis. Here, we investigate C. neoformans strains in which the corresponding gene has been deleted (cxt1Delta). Loss of CXT1 does not affect in vitro growth of the mutant cells or the general morphology of their capsules. However, NMR structural analysis of the two main capsule polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM), showed that both were missing beta1,2-xylose residues. There was an approximately 30% reduction in the abundance of this residue in GXM in mutant compared with wild-type strains, and mutant GalXM was almost completely devoid of beta1,2-linked xylose. The GalXM from the mutant strain was also missing a beta1,3-linked xylose residue. Furthermore, deletion of CXT1 led to attenuation of cryptococcal growth in a mouse model of infection, suggesting that the affected xylose residues are important for normal host-pathogen interactions. Cxt1p is the first glycosyltransferase with a defined role in C. neoformans capsule biosynthesis, and cxt1Delta is the only strain identified to date with structural alterations of the capsule polysaccharide GalXM.
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA.
authors.forename: J Stacey
authors.initials: JS
authors.lastname: Klutts
authors.forename: Tamara L
authors.initials: TL
authors.lastname: Doering
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000096:biosynthesis* / Q000737:chemistry; D003453:Cryptococcosis / Q000473:pathology; D003455:Cryptococcus neoformans / Q000737:chemistry / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D005260:Female; D017353:Gene Deletion; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008810:Mice, Inbred C57BL; D050296:Microbial Viability; D010430:Pentosyltransferases / Q000235:genetics / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D000097608:UDP Xylose-Protein Xylosyltransferase
chemical_list: D010430:Pentosyltransferases; D011135:Polysaccharides, Bacterial; D000097608:UDP Xylose-Protein Xylosyltransferase