title: Role of the synthase domain of Ags1p in cell wall alpha-glucan biosynthesis in fission yeast.
abstract: The cell wall is important for maintenance of the structural integrity and morphology of fungal cells. Besides beta-glucan and chitin, alpha-glucan is a major polysaccharide in the cell wall of many fungi. In the fission yeast Schizosaccharomyces pombe, cell wall alpha-glucan is an essential component, consisting mainly of (1,3)-alpha-glucan with approximately 10% (1,4)-linked alpha-glucose residues. The multidomain protein Ags1p is required for alpha-glucan biosynthesis and is conserved among cell wall alpha-glucan-containing fungi. One of its domains shares amino acid sequence motifs with (1,4)-alpha-glucan synthases such as bacterial glycogen synthases and plant starch synthases. Whether Ags1p is involved in the synthesis of the (1,4)-alpha-glucan constituent of cell wall alpha-glucan had remained unclear. Here, we show that overexpression of Ags1p in S. pombe cells results in accumulation of (1,4)-alpha-glucan. To determine whether the synthase domain of Ags1p is responsible for this activity, we overexpressed Ags1p-E1526A, which carries a mutation in a putative catalytic residue of the synthase domain, but observed no accumulation of (1,4)-alpha-glucan. Compared with wild-type Ags1p, this mutant Ags1p showed a markedly reduced ability to complement the cell lysis phenotype of the temperature-sensitive ags1-1 mutant. Therefore, we conclude that, in S. pombe, the production of (1,4)-alpha-glucan by the synthase domain of Ags1p is important for the biosynthesis of cell wall alpha-glucan.
authors.affiliation: Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Alina
authors.initials: A
authors.lastname: Vos
authors.forename: Nick
authors.initials: N
authors.lastname: Dekker
authors.forename: Ben
authors.initials: B
authors.lastname: Distel
authors.forename: Jack A M
authors.initials: JA
authors.lastname: Leunissen
authors.forename: Frans
authors.initials: F
authors.lastname: Hochstenbach
mesh_terms: D002473:Cell Wall / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005936:Glucans / Q000096:biosynthesis*; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D005936:Glucans; D029702:Schizosaccharomyces pombe Proteins; D005964:Glucosyltransferases; C114021:ags1 protein, S pombe