title: Proline transport and stress tolerance of ammonia-insensitive mutants of the PUT4-encoded proline-specific permease in yeast.
abstract: The imino amino acid, proline, has roles in both cellular nutrition and response to stress. Proline uptake in Saccharomyces cerevisiae is largely mediated by a high affinity, specific permease, Put4p, and a low affinity general amino acid permease, Gap1p. Both are subject to nitrogen catabolite repression (NCR) and nitrogen catabolite inactivation (NCI). In order for proline to be fully exploited, its transport must be derepressed, as occurs upon depletion of preferred nitrogen sources, and molecular oxygen must be present to allow the first step of catabolism via proline oxidase. This study focuses on the isolation of variants of Put4p, which are insensitive to repression by a preferred nitrogen source (ammonia) and their subsequent effect on proline transport and stress tolerance. Specific amino acid residues in the carboxy-terminal region of Put4p were targeted by site-directed mutagenesis. Substitution at Serine(605), a potential phosphorylation target, led to the amelioration of ammonia-induced down-regulation of Put4p. When combined with a promoter mutation (-160), the S(605)A mutation resulted in increased proline uptake and accumulation. This increase in proline accumulation was associated with increased cell viability in conditions of high temperature and osmotic stress raising possible benefits in industrial fermentation applications.
authors.affiliation: School of Agriculture, Food and Wine, The University of Adelaide, Glen Osmond, Australia.
authors.forename: Kate
authors.initials: K
authors.lastname: Poole
authors.forename: Michelle
authors.initials: M
authors.lastname: E Walker
authors.forename: Tristan
authors.initials: T
authors.lastname: Warren
authors.forename: Jennie
authors.initials: J
authors.lastname: Gardner
authors.forename: Colin
authors.initials: C
authors.lastname: McBryde
authors.forename: Miguel
authors.initials: M
authors.lastname: de Barros Lopes
authors.forename: Vladimir
authors.initials: V
authors.lastname: Jiranek
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics* / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism / Q000494:pharmacology*; D015966:Gene Expression Regulation, Fungal; D018869:Heat-Shock Response; D007218:Industrial Microbiology / Q000379:methods; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009584:Nitrogen; D009997:Osmotic Pressure; D011392:Proline / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D000641:Ammonia; C033082:proline transporter; D011392:Proline; D009584:Nitrogen