RESUMO
Two-component signal transducers, which are characterized by the histidine-to-aspartate phospho-transfer mechanism, were once thought to be restricted to prokaryotes. They have, however, now been identified in diverse eukaryotic species including plant, fungus, yeast and slime mold. In yeast, a two-component osmosensor has been found to regulate a mitogen-activated protein kinase (MAPK) cascade, a ubiquitous eukaryotic signaling module.
Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Proteínas de Escherichia coli , Complexos Multienzimáticos , Transdução de Sinais , Proteínas da Membrana Bacteriana Externa , Células Eucarióticas , Fosforilação , Plantas , Células Procarióticas , Saccharomyces cerevisiaeRESUMO
In response to increases in extracellular osmolarity, Saccharomyces cerevisiae activates the HOG1 mitogen-activated protein kinase (MAPK) cascade, which is composed of a pair of redundant MAPK kinase kinases, namely, Ssk2p and Ssk22p, the MAPK kinase Pbs2p, and the MAPK Hog1p. Hog1p is activated by Pbs2p through phosphorylation of specific threonine and tyrosine residues. Activated Hog1p is essential for survival of yeast cells at high osmolarity. However, expression of constitutively active mutant kinases, such as those encoded by SSK2deltaN and PBS2(DD), is toxic and results in a lethal level of Hog1p activation. Overexpression of the protein tyrosine phosphatase Ptp2p suppresses the lethality of these mutations by dephosphorylating Hog1p. A catalytically inactive Cys-to-Ser Ptp2p mutant (Ptp2(C/S)p) is tightly bound to tyrosine-phosphorylated Hog1p in vivo. Disruption of PTP2 leads to elevated levels of tyrosine-phosphorylated Hog1p following exposure of cells to high osmolarity. Disruption of both PTP2 and another protein tyrosine phosphatase gene, PTP3, results in constitutive Hog1p tyrosine phosphorylation even in the absence of increased osmolarity. Thus, Ptp2p and Ptp3p are the major phosphatases responsible for the tyrosine dephosphorylation of Hog1p. When catalytically inactive Hog1(K/N)p is expressed in hog1delta cells, it is constitutively tyrosine phosphorylated. In contrast, Hog1(K/N)p, expressed together with wild-type Hog1p, is tyrosine phosphorylated only when cells are exposed to high osmolarity. Thus, the kinase activity of Hog1p is required for its own tyrosine dephosphorylation. Northern blot analyses suggest that Hog1p regulates Ptp2p and/or Ptp3p activity at the posttranscriptional level.
Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Quinases de Proteína Quinase Ativadas por Mitógeno , Proteínas Quinases Ativadas por Mitógeno , Proteínas Tirosina Fosfatases/metabolismo , Proteínas de Protozoários/metabolismo , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/enzimologia , Proteínas Quinases Dependentes de Cálcio-Calmodulina/genética , Proteínas Fúngicas/genética , Expressão Gênica , Regulação Fúngica da Expressão Gênica/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular , MAP Quinase Quinase Quinases , Mutação , Concentração Osmolar , Fosforilação , Ligação Proteica , Proteínas Quinases/genética , Proteínas Serina-Treonina Quinases/genética , Proteína Tirosina Fosfatase não Receptora Tipo 11 , Proteínas Tirosina Fosfatases/genética , Proteínas de Protozoários/genética , RNA Fúngico , RNA Mensageiro/análise , Saccharomyces cerevisiae/genética , Supressão Genética , Tirosina/metabolismoRESUMO
An osmosensing mechanism in the budding yeast (Saccharomyces cerevisiae) involves both a two-component signal transducer (Sln1p, Ypd1p and Ssk1p) and a MAP kinase cascade (Ssk2p/Ssk22p, Pbs2p, and Hog1p). The transmembrane protein Sln1p contains an extracellular sensor domain and cytoplasmic histidine kinase and receiver domains, whereas the cytoplasmic protein Ssk1p contains a receiver domain. Ypd1p binds to both Sln1p and Ssk1p and mediates the multistep phosphotransfer reaction (phosphorelay). This phosphorelay system is initiated by the autophosphorylation of Sln1p at His576. This phosphate is then sequentially transferred to Sln1p-Asp-1144, then to Ypd1p-His64, and finally to Ssk1p-Asp554. We propose that the multistep phosphorelay mechanism is a universal signal transduction apparatus utilized both in prokaryotes and eukaryotes.
Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Proteínas Quinases Ativadas por Mitógeno , Proteínas Quinases , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/metabolismo , Equilíbrio Hidroeletrolítico/fisiologia , Sequência de Aminoácidos , Ácido Aspártico/metabolismo , Sítios de Ligação , Clonagem Molecular , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Genes Fúngicos , Histidina/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular , Dados de Sequência Molecular , Fenótipo , Fosforilação , Saccharomyces cerevisiae/genética , Transdução de Sinais/fisiologiaRESUMO
In the prokaryotic two-component signal transduction systems, recognition of an environmental stimulus by a sensor molecule results in the activation of its histidine kinase domain and phosphorylation of a histidine residue within that domain. This phosphate group is then transferred to an aspartate residue in the receiver domain of a cognate response regulator molecule, resulting in the activation of its output function. Although a few eukaryotic proteins were identified recently that show sequence similarity to the prokaryotic sensors or response regulators, it has not been clear whether they constituted a part of a 'two-component' system. Here we describe a two-component system in Saccharomyces cerevisiae that regulates an osmosensing MAP kinase cascade.
