title: Comprehensive proteomic analysis of Saccharomyces cerevisiae cell walls: identification of proteins covalently attached via glycosylphosphatidylinositol remnants or mild alkali-sensitive linkages.
abstract: The cell wall of yeast contains proteins that are covalently bound to the glycan network. These cell wall proteins (CWPs) mediate cell-cell interactions and may be involved in cell wall biosynthesis. Using tandem mass spectrometry, we have identified 19 covalently bound CWPs of Saccharomyces cerevisiae. Twelve of them are shown for the first time to be covalently incorporated into the cell wall. The identified proteins include 12 predicted glycosylphosphatidylinositol-modified CWPs, all four members of the Pir protein family, and three additional proteins (Scw4p, Scw10p, and Tos1p) that are, like Pir proteins, connected to the cell wall glycan network via an alkali-sensitive linkage. However, Scw4p, Scw10p, and Tos1p do not contain internal repeat sequences shown to be essential for Pir protein incorporation and may represent a separate class of CWPs. Strikingly, seven of the identified proteins (Gas1p, Gas3p, Gas5p, Crh1p, Utr2p, Scw4p, and Scw10p) are classified as glycoside hydrolases. Phenotypic analysis of deletion mutants lacking the corresponding CWP-encoding genes indicated that most of them have altered cell wall properties, which reinforces the importance of the identified proteins for proper cell wall formation. In particular, gas1Delta and ecm33Delta were highly sensitive to Calcofluor White and high temperature, whereas gas1Delta, scw4Delta, and tos1Delta were highly resistant to incubation with beta-1,3-glucanase. The CWP identification method developed here relies on directly generating tryptic peptides from isolated cell walls and is independent of the nature of the covalent linkages between CWPs and cell wall glycans. Therefore, it will probably be equally effective in many other fungi.
authors.affiliation: Laboratory for Mass Spectrometry of Biomacromolecules, Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
authors.forename: Qing Yuan
authors.initials: QY
authors.lastname: Yin
authors.forename: Piet W J
authors.initials: PW
authors.lastname: de Groot
authors.forename: Henk L
authors.initials: HL
authors.lastname: Dekker
authors.forename: Luitzen
authors.initials: L
authors.lastname: de Jong
authors.forename: Frans M
authors.initials: FM
authors.lastname: Klis
authors.forename: Chris G
authors.initials: CG
authors.lastname: de Koster
mesh_terms: D000595:Amino Acid Sequence; D002176:Candida albicans / Q000737:chemistry; D002473:Cell Wall / Q000737:chemistry*; D006023:Glycoproteins; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010641:Phenotype; D040901:Proteomics; D020449:Repetitive Sequences, Amino Acid; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D017261:Glycosylphosphatidylinositols; C074229:HSP150 protein, S cerevisiae; D006360:Heat-Shock Proteins; D010446:Peptide Fragments; D029701:Saccharomyces cerevisiae Proteins; D014357:Trypsin