Wang J D, Michelitsch M D, Weissman J S
Department of Pharmacology, University of California-San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143-0450, USA.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12163-8. doi: 10.1073/pnas.95.21.12163.
The chaperonin GroEL is an oligomeric double ring structure that, together with the cochaperonin GroES, assists protein folding. Biochemical analyses indicate that folding occurs in a cis ternary complex in which substrate is sequestered within the GroEL central cavity underneath GroES. Recently, however, studies of GroEL "minichaperones" containing only the apical substrate binding subdomain have questioned the functional importance of substrate encapsulation within GroEL-GroES complexes. Minichaperones were reported to assist folding despite the fact that they are monomeric and therefore cannot form a central cavity. Here we compare directly the folding activity of minichaperones with that of the full GroEL-GroES system. In agreement with earlier studies, minichaperones assist folding of some proteins. However, this effect is observed only under conditions where substantial spontaneous folding is also observed and is indistinguishable from that resulting from addition of the nonchaperone protein alpha-casein. By contrast, the full GroE system efficiently promotes folding of several substrates under conditions where essentially no spontaneous folding is observed. These data argue that the full GroEL folding activity requires the intact GroEL-GroES complex, and in light of previous studies, underscore the importance of substrate encapsulation for providing a folding environment distinct from the bulk solution.
伴侣蛋白GroEL是一种寡聚双环结构，它与共伴侣蛋白GroES一起协助蛋白质折叠。生化分析表明，折叠发生在一个顺式三元复合物中，其中底物被隔离在GroES下方的GroEL中央腔内。然而，最近对仅包含顶端底物结合亚结构域的GroEL“微型伴侣蛋白”的研究，对底物在GroEL - GroES复合物中被包裹的功能重要性提出了质疑。据报道，微型伴侣蛋白尽管是单体的，因此不能形成中央腔，但仍能协助折叠。在这里，我们直接比较了微型伴侣蛋白与完整的GroEL - GroES系统的折叠活性。与早期研究一致，微型伴侣蛋白能协助一些蛋白质的折叠。然而，这种效应仅在也观察到大量自发折叠的条件下才会出现，并且与添加非伴侣蛋白α-酪蛋白所产生的效应无法区分。相比之下，完整的GroE系统在基本上没有观察到自发折叠的条件下，能有效地促进几种底物的折叠。这些数据表明，完整的GroEL折叠活性需要完整的GroEL - GroES复合物，并且根据先前的研究，强调了底物包裹对于提供一个不同于本体溶液的折叠环境的重要性。
