title: Sbe2p and sbe22p, two homologous Golgi proteins involved in yeast cell wall formation.
abstract: The cell wall of fungal cells is important for cell integrity and cell morphogenesis and protects against harmful environmental conditions. The yeast cell wall is a complex structure consisting mainly of mannoproteins, glucan, and chitin. The molecular mechanisms by which the cell wall components are synthesized and transported to the cell surface are poorly understood. We have identified and characterized two homologous yeast proteins, Sbe2p and Sbe22p, through their suppression of a chs5 spa2 mutant strain defective in chitin synthesis and cell morphogenesis. Although sbe2 and sbe22 null mutants are viable, sbe2 sbe22 cells display several phenotypes indicative of defects in cell integrity and cell wall structure. First, sbe2 sbe22 cells display a sorbitol-remediable lysis defect at 37 degrees C and are hypersensitive to SDS and calcofluor. Second, electron microscopic analysis reveals that sbe2 sbe22 cells have an aberrant cell wall structure with a reduced mannoprotein layer. Finally, immunofluorescence experiments reveal that in small-budded cells, sbe2 sbe22 mutants mislocalize Chs3p, a protein involved in chitin synthesis. In addition, sbe2 sbe22 diploids have a bud-site selection defect, displaying a random budding pattern. A Sbe2p-GFP fusion protein localizes to cytoplasmic patches, and Sbe2p cofractionates with Golgi proteins. Deletion of CHS5, which encodes a Golgi protein involved in the transport of Chs3p to the cell periphery, is lethal in combination with disruption of SBE2 and SBE22. Thus, we suggest a model in which Sbe2p and Sbe22p are involved in the transport of cell wall components from the Golgi apparatus to the cell surface periphery in a pathway independent of Chs5p.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA.
authors.forename: B
authors.initials: B
authors.lastname: Santos
authors.forename: M
authors.initials: M
authors.lastname: Snyder
mesh_terms: D000595:Amino Acid Sequence; D001557:Benzenesulfonates / Q000378:metabolism; D002455:Cell Division; D016764:Cell Polarity; D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure; D002687:Chitin Synthase / Q000032:analysis / Q000235:genetics; D003593:Cytoplasm / Q000737:chemistry; D003598:Cytoskeletal Proteins; D004843:Epistasis, Genetic; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics / Q000502:physiology; D005804:Genes, Lethal / Q000235:genetics; D043326:Glucan 1,3-beta-Glucosidase; D006026:Glycoside Hydrolases / Q000378:metabolism; D006056:Golgi Apparatus / Q000737:chemistry* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D012967:Sodium Dodecyl Sulfate / Q000378:metabolism; D013489:Suppression, Genetic / Q000235:genetics; D033921:Vesicular Transport Proteins; D043324:beta-Fructofuranosidase; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D001557:Benzenesulfonates; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; D008562:Membrane Glycoproteins; C405427:SBE2 protein, S cerevisiae; C541666:SBE22 protein, S cerevisiae; C065889:SPA2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D012967:Sodium Dodecyl Sulfate; C007061:C.I. Fluorescent Brightening Agent 28; C491360:CHS5 protein, S cerevisiae; D002687:Chitin Synthase; D006026:Glycoside Hydrolases; D001617:beta-Glucosidase; D043324:beta-Fructofuranosidase; D043326:Glucan 1,3-beta-Glucosidase