Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA.
Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):16107-12. doi: 10.1073/pnas.1214447109. Epub 2012 Sep 17.
The type II p21-activated kinases (PAKs) are key effectors of RHO-family GTPases involved in cell motility, survival, and proliferation. Using a structure-guided approach, we discovered that type II PAKs are regulated by an N-terminal autoinhibitory pseudosubstrate motif centered on a critical proline residue, and that this regulation occurs independently of activation loop phosphorylation. We determined six X-ray crystal structures of either full-length PAK4 or its catalytic domain, that demonstrate the molecular basis for pseudosubstrate binding to the active state with phosphorylated activation loop. We show that full-length PAK4 is constitutively autoinhibited, but mutation of the pseudosubstrate releases this inhibition and causes increased phosphorylation of the apoptotic regulation protein Bcl-2/Bcl-X(L) antagonist causing cell death and cellular morphological changes. We also find that PAK6 is regulated by the pseudosubstrate region, indicating a common type II PAK autoregulatory mechanism. Finally, we find Src SH3, but not β-PIX SH3, can activate PAK4. We provide a unique understanding for type II PAK regulation.
II 型 p21 激活激酶（PAKs）是 RHO 家族 GTPases 的关键效应物，参与细胞运动、存活和增殖。我们采用结构导向方法发现，II 型 PAK 受到以关键脯氨酸残基为中心的 N 端自动抑制假底物基序调控，这种调控独立于激活环磷酸化。我们测定了全长 PAK4 或其催化结构域的六个 X 射线晶体结构，证明了假底物与磷酸化激活环的活性状态结合的分子基础。我们表明全长 PAK4 是组成性自动抑制的，但假底物的突变会解除这种抑制，导致凋亡调节蛋白 Bcl-2/Bcl-X(L)拮抗剂的磷酸化增加，从而导致细胞死亡和细胞形态变化。我们还发现 PAK6 受假底物区域调控，表明存在共同的 II 型 PAK 自我调控机制。最后，我们发现 Src SH3，但不是 β-PIX SH3，可以激活 PAK4。我们为 II 型 PAK 调控提供了独特的理解。
