Mutations in Fks1p affect the cell wall content of beta-1,3- and beta-1,6-glucan in Saccharomyces cerevisiae.
Fks1p and Fks2p are related proteins thought to be catalytic subunits of the beta-1,3-glucan synthase. Analysis of fks1 delta mutants showed a partial K1 killer toxin-resistant phenotype and a 30% reduction in alkali-soluble beta-1,3-glucan that was accompanied by a modest reduction in beta-1,6-glucan. The gas1 delta mutant lacking a 1,3-beta-glucanosyltransferase displayed a similar reduction in alkali-soluble beta-1,3-glucan but did not share the beta-1,6-glucan defect, indicating that beta-1,6-glucan reduction is not a general phenotype among beta-1,3-glucan biosynthetic mutants. Overexpression of FKS2 suppressed the killer toxin phenotype of fks1 delta mutants, implicating Fks2p in the biosynthesis of the residual beta-1,6-glucan present in fks1 delta cells. In addition, eight out of 12 fks1ts fks2 delta mutants had altered beta-glucan levels at the permissive temperature: the partial killer resistant FKS1F1258Y N1520D allele was severely affected in both polymers and displayed a 55% reduction in beta-1,6-glucan, while the in vitro hyperactive allele FKS1T605I M761T increased both beta-glucan levels. These beta-1,6-glucan phenotypes may be due to altered availability of, and structural changes in, the beta-1,3-glucan polymer, which might serve as a beta-1,6-glucan acceptor at the cell surface. Alternatively, Fks1p and Fks2p could actively participate in the biosynthesis of both polymers as beta-glucan transporters. We analysed Fks1p and Fks2p in beta-1,6-glucan deficient mutants and found that they were mislocalized and that the mutants had reduced in vitro glucan synthase activity, possibly contributing to the observed beta-1,6-glucan defects.
Department of Biology, McGill University, 1205 Dr. Penfield Ave., Montreal, Quebec, Canada H3A 1B1.
Gerrit J P
GJ
Dijkgraaf
Mitsuhiro
M
Abe
Yoshikazu
Y
Ohya
Howard
H
Bussey
D015153:Blotting, Western; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D054714:Echinocandins; D000939:Epitopes; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005936:Glucans / Q000096:biosynthesis*; D005964:Glucosyltransferases / Q000378:metabolism; D055646:Killer Factors, Yeast; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009183:Mycotoxins / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D047071:beta-Glucans
D004271:DNA, Fungal; D054714:Echinocandins; D000939:Epitopes; D005656:Fungal Proteins; D005936:Glucans; C089359:K1 killer toxin; D055646:Killer Factors, Yeast; D008565:Membrane Proteins; D009183:Mycotoxins; D029701:Saccharomyces cerevisiae Proteins; D047071:beta-Glucans; C064197:beta-1,6-glucan; C033363:beta-1,3-glucan; D005964:Glucosyltransferases; C040232:glucan synthase; C091618:FKS1 protein, S cerevisiae; C095724:GSC2 protein, S cerevisiae