Hayer-Hartl M K, Weber F, Hartl F U
Howard Hughes Medical Institute and Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
EMBO J. 1996 Nov 15;15(22):6111-21.
As a basic principle, assisted protein folding by GroEL has been proposed to involve the disruption of misfolded protein structures through ATP hydrolysis and interaction with the cofactor GroES. Here, we describe chaperonin subreactions that prompt a re-examination of this view. We find that GroEL-bound substrate polypeptide can induce GroES cycling on and off GroEL in the presence of ADP. This mechanism promotes efficient folding of the model protein rhodanese, although at a slower rate than in the presence of ATP. Folding occurs when GroES displaces the bound protein into the sequestered volume of the GroEL cavity. Resulting native protein leaves GroEL upon GroES release. A single-ring variant of GroEL is also fully functional in supporting this reaction cycle. We conclude that neither the energy of ATP hydrolysis nor the allosteric coupling of the two GroEL rings is directly required for GroEL/GroES-mediated protein folding. The minimal mechanism of the reaction is the binding and release of GroES to a polypeptide-containing ring of GroEL, thereby closing and opening the GroEL folding cage. The role of ATP hydrolysis is mainly to induce conformational changes in GroEL that result in GroES cycling at a physiologically relevant rate.
作为一项基本原则，有人提出GroEL辅助蛋白质折叠涉及通过ATP水解以及与辅因子GroES相互作用来破坏错误折叠的蛋白质结构。在此，我们描述了伴侣蛋白的子反应，这些反应促使人们重新审视这一观点。我们发现，在存在ADP的情况下，与GroEL结合的底物多肽可诱导GroES在GroEL上循环结合和解离。这种机制促进了模型蛋白硫氰酸酶的有效折叠，尽管其速率比存在ATP时要慢。当GroES将结合的蛋白质置换到GroEL腔的隔离空间中时，折叠发生。产生的天然蛋白质在GroES释放时离开GroEL。GroEL的单环变体在支持这个反应循环方面也完全具有功能。我们得出结论，GroEL/GroES介导的蛋白质折叠既不直接需要ATP水解的能量，也不直接需要两个GroEL环之间的变构偶联。该反应的最小机制是GroES与含有多肽的GroEL环的结合和解离，从而关闭和打开GroEL折叠笼。ATP水解的作用主要是诱导GroEL的构象变化，从而使GroES以生理相关的速率循环。
