title: Molecular and phenotypic analysis of CaVRG4, encoding an essential Golgi apparatus GDP-mannose transporter.
abstract: Cell surface mannan is implicated in almost every aspect of pathogenicity of Candida albicans. In Saccharomyces cerevisiae, the Vrg4 protein acts as a master regulator of mannan synthesis through its role in substrate provision. The substrate for mannosylation of proteins and lipids in the Golgi apparatus is GDP-mannose, whose lumenal transport is catalyzed by Vrg4p. This nucleotide sugar is synthesized in the cytoplasm by pathways that are highly conserved in all eukaryotes, but its lumenal transport (and hence Golgi apparatus-specific mannosylation) is a fungus-specific process. To begin to study the role of Golgi mannosylation in C. albicans, we isolated the CaVRG4 gene and analyzed the effects of loss of its function. CaVRG4 encodes a functional homologue of the S. cerevisiae GDP-mannose transporter. CaVrg4p localized to punctate spots within the cytoplasm of C. albicans in a pattern reminiscent of localization of Vrg4p in the Golgi apparatus in S. cerevisiae. Like partial loss of ScVRG4 function, partial loss of CaVRG4 function resulted in mannosylation defects, which in turn led to a number of cell wall-associated phenotypes. While heterozygotes displayed no growth phenotypes, a hemizygous strain, containing a single copy of CaVRG4 under control of the methionine-repressible MET3 promoter, did not grow in the presence of methionine and cysteine, demonstrating that CaVRG4 is essential for viability. Mutant Candida vrg4 strains were defective in hyphal formation but exhibited a constitutive polarized mode of pseudohyphal growth. Because the VRG4 gene is essential for yeast viability but does not have a mammalian homologue, it is a particularly attractive target for development of antifungal therapies.
authors.affiliation: Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York, Stony Brook, New York 11794-5215, USA.
authors.forename: Akiko
authors.initials: A
authors.lastname: Nishikawa
authors.forename: Jay B
authors.initials: JB
authors.lastname: Poster
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Jigami
authors.forename: Neta
authors.initials: N
authors.lastname: Dean
mesh_terms: D000595:Amino Acid Sequence; D002176:Candida albicans / Q000166:cytology / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D020043:Genes, Essential; D005800:Genes, Fungal; D006031:Glycosylation; D006056:Golgi Apparatus / Q000235:genetics* / Q000378:metabolism; D008351:Mannans / Q000096:biosynthesis*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009024:Morphogenesis; D009154:Mutation; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D005656:Fungal Proteins; D008351:Mannans; D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; C443979:VRG4 protein, Candida albicans; C099493:VRG4 protein, S cerevisiae