von Plehwe Ulrike, Berndt Uta, Conz Charlotte, Chiabudini Marco, Fitzke Edith, Sickmann Albert, Petersen Astrid, Pfeifer Dietmar, Rospert Sabine
Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, D-79104 Freiburg, Germany.
Genes Dev. 2009 Sep 1;23(17):2102-15. doi: 10.1101/gad.529409.
Yeast senses the availability of external energy sources via multiple interconnected signaling networks. One of the central components is SNF1, the homolog of mammalian AMP-activated protein kinase, which in yeast is essential for the expression of glucose-repressed genes. When glucose is available hyperphosphorylated SNF1 is rendered inactive by the type 1 protein phosphatase Glc7. Dephosphorylation requires Reg1, which physically targets Glc7 to SNF1. Here we show that the chaperone Ssb is required to keep SNF1 in the nonphosphorylated state in the presence of glucose. Using a proteome approach we found that the Deltassb1Deltassb2 strain displays alterations in protein expression and suffers from phenotypic characteristics reminiscent of glucose repression mutants. Microarray analysis revealed a correlation between deregulation on the protein and on the transcript level. Supporting studies uncovered that SSB1 was an effective multicopy suppressor of severe growth defects caused by the Deltareg1 mutation. Suppression of Deltareg1 by high levels of Ssb was coupled to a reduction of Snf1 hyperphosphorylation back to the wild-type phosphorylation level. The data are consistent with a model in which Ssb is crucial for efficient regulation within the SNF1 signaling network, thereby allowing an appropriate response to changing glucose levels.
酵母通过多个相互连接的信号网络感知外部能量来源的可用性。其中一个核心组件是SNF1，它是哺乳动物AMP激活蛋白激酶的同源物，在酵母中对于葡萄糖抑制基因的表达至关重要。当有葡萄糖时，1型蛋白磷酸酶Glc7使过度磷酸化的SNF1失活。去磷酸化需要Reg1，它将Glc7靶向SNF1。在这里，我们表明伴侣蛋白Ssb在有葡萄糖存在的情况下需要保持SNF1处于非磷酸化状态。使用蛋白质组学方法我们发现缺失Ssb1和Ssb2的菌株在蛋白质表达上有改变，并具有类似于葡萄糖抑制突变体的表型特征。微阵列分析揭示了蛋白质水平和转录水平失调之间的相关性。支持性研究发现SSB1是由缺失Reg1突变引起的严重生长缺陷的有效多拷贝抑制因子。高水平的Ssb对缺失Reg1的抑制作用与Snf1过度磷酸化水平降低回到野生型磷酸化水平相关。这些数据与一个模型一致，即Ssb在SNF1信号网络内的有效调节中至关重要，从而允许对变化的葡萄糖水平做出适当反应。
