Rho-associated protein kinase 2 (ROCK2) is a membrane-anchored, long, flexible, multidomain, multifunctional protein. Its functions can be divided into two categories: membrane-proximal and membrane-distal. A recent study concluded that membrane-distal functions require the fully extended conformation, and this conclusion was supported by electron microscopy. The present solution small-angle X-ray scattering (SAXS) study revealed that ROCK2 population is a dynamic mixture of folded and partially extended conformers. Binding of RhoA to the coiled-coil domain shifts the equilibrium towards the partially extended state. Enzyme activity measurements suggest that the binding of natural protein substrates to the kinase domain breaks up the interaction between the N-terminal kinase and C-terminal regulatory domains, but smaller substrate analogues do not. The present study reveals the dynamic behaviour of this long, dimeric molecule in solution, and our structural model provides a mechanistic explanation for a set of membrane-proximal functions while allowing for the existence of an extended conformation in the case of membrane-distal functions.

Rho相关蛋白激酶2（ROCK2）是膜锚定的，长的，柔性的，多域，多功能蛋白。它的功能可以分为两类：近膜和远膜。最近的一项研究得出结论，膜远端功能需要完全扩展的构象，这一结论得到了电子显微镜的支持。本解决方案小角度X射线散射（SAXS）研究表明，ROCK2群体是折叠和部分延伸构象异构体的动态混合物。RhoA与卷曲螺旋结构域的结合将平衡移向部分延伸状态。酶活性测量表明，天然蛋白底物与激酶结构域的结合破坏了N端激酶和C端调节域之间的相互作用，但较小的底物类似物却没有。