Shevchenko Ekaterina, Poso Antti, Pantsar Tatu
Dept of Internal Medicine VIII, University Hospital Tübingen, Otfried-Müller-Strasse 14, 72076 Tübingen, Germany.
School of Pharmacy, University of Eastern Finland, Yliopistonranta 1C, 70210 Kuopio, Finland.
Comput Struct Biotechnol J. 2020 Sep 20;18:2687-2698. doi: 10.1016/j.csbj.2020.09.017. eCollection 2020.
Protein kinases are crucial components of the cell-signalling machinery that orchestrate and convey messages to their downstream targets. Most often, kinases are activated upon a phosphorylation to their activation loop, which will shift the kinase into the active conformation. The Dual specificity mitogen-activated protein kinase kinase 4 (MKK4) exists in a unique conformation in its inactive unphosphorylated state, where its activation segment appears in a stable α-helical conformation. However, the precise role of this unique conformational state of MKK4 is unknown. Here, by all-atom molecular dynamics simulations (MD simulations), we show that this inactive state is unstable as monomer even when unphosphorylated and that the phosphorylation of the activation segment further destabilizes the autoinhibited α-helix. The specific phosphorylation pattern of the activation segment has also a unique influence on MKK4 dynamics. Furthermore, we observed that this specific inactive state is stable as a dimer, which becomes destabilized upon phosphorylation. Finally, we noticed that the most frequent MKK4 mutation observed in cancer, R134W, which role has not been disclosed to date, contributes to the dimer stability. Based on these data we postulate that MKK4 occurs as a dimer in its inactive autoinhibited state, providing an additional layer for its activity regulation.
蛋白激酶是细胞信号传导机制的关键组成部分，它们协调并将信息传递给下游靶点。大多数情况下，激酶在其激活环发生磷酸化后被激活，这会使激酶转变为活性构象。双特异性丝裂原活化蛋白激酶激酶4（MKK4）在其未磷酸化的无活性状态下以独特的构象存在，其激活片段呈稳定的α螺旋构象。然而，MKK4这种独特构象状态的确切作用尚不清楚。在这里，通过全原子分子动力学模拟（MD模拟），我们表明即使未磷酸化，这种无活性状态作为单体也是不稳定的，并且激活片段的磷酸化会进一步破坏自抑制α螺旋的稳定性。激活片段的特定磷酸化模式对MKK4动力学也有独特影响。此外，我们观察到这种特定的无活性状态作为二聚体是稳定的，磷酸化后会变得不稳定。最后，我们注意到在癌症中观察到的最常见的MKK4突变R134W（其作用迄今尚未公开）有助于二聚体的稳定性。基于这些数据，我们推测MKK4在其无活性的自抑制状态下以二聚体形式存在，为其活性调节提供了额外的层面。
