title: A novel role of the yeast CaaX protease Ste24 in chitin synthesis.
abstract: Ste24 is a membrane-integral CaaX metalloprotease residing in the endoplasmic reticulum (ER). In yeast, the only known substrate of Ste24 is the mating factor a precursor. A global screening for protein-protein interactions indicated that Ste24 interacts with chitin synthesis deficient (Chs)3, an enzyme required for chitin synthesis. We confirmed this interaction by yeast two-hybrid analyses and mapped the interacting cytoplasmic domains. Next, we investigated the influence of Ste24 on chitin synthesis. In sterile (ste)24Delta mutants, we observed resistance to calcofluor white (CFW), which was also apparent when the cells expressed a catalytically inactive version of Ste24. In addition, ste24Delta cells showed a decrease in chitin levels and Chs3-green fluorescent protein localized less frequently at the bud neck. Overexpression of STE24 resulted in hypersensitivity to CFW and a slight increase in chitin levels. The CFW phenotype of ste24Delta cells could be rescued by its human and insect orthologues. Although Chs3 binds to Ste24, it seems not to be a substrate for this protease. Instead, our data suggest that Chs3 and Ste24 form a complex in the ER that facilitates protease action on prenylated Chs4, a known activator of Chs3 with a C-terminal CaaX motif, leading to a more efficient localization of Chs3 at the plasma membrane.
authors.affiliation: Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany.
authors.forename: Derek
authors.initials: D
authors.lastname: Meissner
authors.forename: Jothini
authors.initials: J
authors.lastname: Odman-Naresh
authors.forename: Inga
authors.initials: I
authors.lastname: Vogelpohl
authors.forename: Hans
authors.initials: H
authors.lastname: Merzendorfer
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001557:Benzenesulfonates / Q000494:pharmacology; D055162:Biocatalysis / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002686:Chitin / Q000096:biosynthesis*; D002687:Chitin Synthase / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D015151:Immunoblotting; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000737:chemistry / Q000378:metabolism*; D054876:Prenylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity / Q000187:drug effects; D014231:Tribolium
chemical_list: D001557:Benzenesulfonates; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D002686:Chitin; C007061:C.I. Fluorescent Brightening Agent 28; C069390:CHS3 protein, S cerevisiae; D002687:Chitin Synthase; D008666:Metalloendopeptidases; C491251:STE24 protein, S cerevisiae