Activation of the yeast SSK2 MAP kinase kinase kinase by the SSK1 two-component response regulator
Activation of the yeast SSK2 MAP kinase kinase kinase by the SSK1 two-component response regulator
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DOI：
10.1093/emboj/17.5.1385
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发表时间：
1998-03-02
期刊：
影响因子：
11.4
通讯作者：
Saito, H
中科院分区：
文献类型：
--
作者：
Posas, F;Saito, H
酵母细胞暴露于增加的细胞外渗透压浓度诱导HOG 1促分裂原活化蛋白激酶（MAPK）级联，其由SSK 2、SSK 22和STE 11 MAPK、PBS 2 MAPK和HOG 1 MAPK组成。SSK 2/SSK 22 MAPK被由SLN 1、YPD 1和SSK 1组成的“双组分”MAPK传感器激活。SSK 1 C-末端受体结构域与SSK 2的N-末端区段相互作用，在高渗处理后，SSK 2迅速自磷酸化，并且该反应需要SSK 1与SSK 2的相互作用。SSK 2的自磷酸化是分子内反应，表明与哺乳动物MEKK 1激酶相似。SSK 2的去磷酸化使激酶失活，但它可以通过体外加入SSK 1而重新激活，SSK 2激活环中的一个保守的苏氨酸残基（Thr 1460）对激酶活性具有重要作用。基于这些观察，我们提出了SSK 2 MAPKKK的两步激活机制，第一步，SSK 1与SSK 2的N-末端结构域中的SSK 1结合位点的结合引起SSK 2的构象变化并诱导其潜在的激酶活性。在第二步中，SSK 2的自磷酸化使其活性不依赖于SSK 1的存在，类似的机制可能适用于来自酵母和高等真核生物的其他MAPKKK。
Exposure of yeast cells to increased extracellular osmolarity induces the HOG1 mitogen-activated protein kinase (MAPK) cascade, which is composed of SSK2, SSK22 and STE11 MAPKKKs, PBS2 MAPKK and HOG1 MAPK, The SSK2/SSK22 MAPKKKs are activated by a 'two-component' osmosensor composed of SLN1, YPD1 and SSK1, The SSK1 C-terminal receiver domain interacts with an N-terminal segment of SSK2, Upon hyperosmotic treatment, SSK2 is autophosphorylated rapidly, and this reaction requires the interaction of SSK1 with SSK2, Autophosphorylation of SSK2 is an intramolecular reaction, suggesting similarity to the mammalian MEKK1 kinase, Dephosphorylation of SSK2 renders the kinase inactive, but it can be re-activated by addition of SSK1 in vitro, A conserved threonine residue (Thr1460) in the activation loop of SSK2 is important for kinase activity, Based on these observations, we propose the following two-step activation mechanism of SSK2 MAPKKK, In the first step, the binding of SSK1 to the SSK1-binding site in the N-terminal domain of SSK2 causes a conformational change in SSK2 and induces its latent kinase activity, In the second step, autophosphorylation of SSK2 renders its activity independent of the presence of SSK1, A similar mechanism might be applicable to other MAPKKKs from both yeast and higher eukaryotes.