Weissman J S, Kashi Y, Fenton W A, Horwich A L
Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06510.
Cell. 1994 Aug 26;78(4):693-702. doi: 10.1016/0092-8674(94)90533-9.
The chaperonin GroEL is a ribosome-sized double-ring structure that assists in folding a diverse set of polypeptides. We have examined the fate of a polypeptide during a chaperonin-mediated folding reaction. Strikingly, we find that, upon addition of ATP and the cochaperonin GroES, polypeptide is released rapidly from GroEL in a predominantly nonnative conformation that can be trapped by mutant forms of GroEL that are capable of binding but not releasing substrate. Released polypeptide undergoes kinetic partitioning: a fraction completes folding while the remainder is rebound rapidly by other GroEL molecules. Folding appears to occur in an all-or-none manner, as proteolysis and tryptophan fluorescence indicate that after rebinding, polypeptide has the same structure as in the original complex. These observations suggest that GroEL functions by carrying out multiple rounds of binding aggregation-prone or kinetically trapped intermediates, maintaining them in an unfolded state, and releasing them to attempt to fold in solution.
伴侣蛋白GroEL是一种核糖体大小的双环结构，可协助多种多肽进行折叠。我们研究了在伴侣蛋白介导的折叠反应中多肽的命运。令人惊讶的是，我们发现，在添加ATP和共伴侣蛋白GroES后，多肽以主要为非天然构象的形式迅速从GroEL中释放出来，这种非天然构象可被能够结合但不能释放底物的GroEL突变形式捕获。释放的多肽进行动力学分配：一部分完成折叠，而其余部分则被其他GroEL分子迅速重新结合。折叠似乎以全或无的方式发生，因为蛋白水解和色氨酸荧光表明，重新结合后，多肽具有与原始复合物相同的结构。这些观察结果表明，GroEL的功能是通过进行多轮结合易于聚集或动力学捕获的中间体，将它们保持在未折叠状态，然后释放它们以尝试在溶液中折叠。
