Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Biochemistry. 2010 Mar 16;49(10):2159-66. doi: 10.1021/bi902171d.
Regulation of the class IA PI 3-kinase involves inhibition and stabilization of the catalytic subunit (p110) by the regulatory subunit (p85). Regulation is achieved by two major contacts: a stable interface involving the adapter-binding domain (ABD) of p110 and the inter-SH2 (iSH2) domain of p85 and a regulatory interaction between the N-terminal SH2 (nSH2) domain of p85 and the helical domain of p110. In the present study, we have examined the relative orientation of the nSH2 and iSH2 of p85alpha using site-directed spin labeling and pulsed EPR. Surprisingly, both distance measurements and distance distributions suggest that the nSH2 domain is highly disordered relative to the iSH2 domain. Molecular modeling based on EPR distance restraints suggests that the nSH2 domain moves in a hinge-like manner, sampling a torus space around the proximal end of the iSH2 domain. These data have important implications for the mechanism by which p85/p110 dimers are regulated by phosphopeptides.
IA 类 PI 3-激酶的调节涉及通过调节亚基（p85）抑制和稳定催化亚基（p110）。调节是通过两个主要接触点实现的：一个涉及 p110 的衔接子结合域（ABD）和 p85 的 inter-SH2（iSH2）域的稳定界面，以及 p85 的 N 端 SH2（nSH2）域和 p110 的螺旋域之间的调节相互作用。在本研究中，我们使用定点旋转标记和脉冲 EPR 检查了 p85alpha 的 nSH2 和 iSH2 的相对取向。令人惊讶的是，两种距离测量和距离分布都表明 nSH2 域相对于 iSH2 域高度无序。基于 EPR 距离约束的分子建模表明，nSH2 域以铰链样方式移动，在 iSH2 域的近端周围采样环面空间。这些数据对 p85/p110 二聚体如何被磷酸肽调节的机制具有重要意义。
