Chaperone Activity of a Chimeric GroEL Protein That Can Exist in a Single or Double Ring Form*
Chaperone Activity of a Chimeric GroEL Protein That Can Exist in a Single or Double Ring Form*
复制标题
以单环或双环形式存在的嵌合 GroEL 蛋白的伴侣活性*
DOI：
10.1074/jbc.274.29.20351
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
P. Lund
中科院分区：
文献类型：
--
作者：
Annette Erbse;O. Yifrach;S. Jones;P. Lund
分子伴侣GroEL是一种由两个环组成的蛋白质复合体，每个环有七个相同的亚基。它的作用被认为是通过提供一个空腔，在其中蛋白质底物可以折叠成一种没有聚集倾向的形式。底物蛋白质在折叠时被隔离在腔内，并通过覆盖腔开放端的GroES复合体的作用阻止其扩散出腔外。GroEL作用机制中的一个关键步骤是在两个环之间传递构象变化，这种变化是由核苷酸与与含有多肽底物相反的GroEL环结合而引起的。这种构象变化随后导致GroE从GroEL中释放，从而使多肽得以释放。因此，预测单环形式的GroEL不能有效地伴随依赖于GroE的底物的折叠，因为它们不能释放结合的GroE和不能释放折叠的蛋白质。我们在这里描述了一个嵌合的GroEL蛋白的详细功能分析，我们证明它存在于单环和双环之间的平衡溶液中。我们证明，虽然GroEL嵌合体的双环形式在依赖于GROE的底物的折叠中有效地发挥作用，但单环形式却不能。然而，嵌合体的单环形式能够伴随底物的折叠，而底物的高效折叠不需要格罗格。我们进一步证明了GroEL的双环结构可能是其体内活性所必需的。
The molecular chaperone GroEL is a protein complex consisting of two rings each of seven identical subunits. It is thought to act by providing a cavity in which a protein substrate can fold into a form that has no propensity to aggregate. Substrate proteins are sequestered in the cavity while they fold, and prevented from diffusion out of the cavity by the action of the GroES complex, that caps the open end of the cavity. A key step in the mechanism of action of GroEL is the transmission of a conformational change between the two rings, induced by the binding of nucleotides to the GroEL ring opposite to the one containing the polypeptide substrate. This conformational change then leads to the discharge of GroES from GroEL, enabling polypeptide release. Single ring forms of GroEL are thus predicted to be unable to chaperone the folding of GroES-dependent substrates efficiently, since they are unable to discharge the bound GroES and unable to release folded protein. We describe here a detailed functional analysis of a chimeric GroEL protein, which we show to exist in solution in equilibrium between single and double ring forms. We demonstrate that whereas the double ring form of the GroEL chimera functions effectively in refolding of a GroES-dependent substrate, the single ring form does not. The single ring form of the chimera, however, is able to chaperone the folding of a substrate that does not require GroES for its efficient folding. We further demonstrate that the double ring structure of GroEL is likely to be required for its activity in vivo.