CONFORMATIONAL SPECIFICITY OF THE CHAPERONIN GROEL FOR THE COMPACT FOLDING INTERMEDIATES OF ALPHA-LACTALBUMIN
CONFORMATIONAL SPECIFICITY OF THE CHAPERONIN GROEL FOR THE COMPACT FOLDING INTERMEDIATES OF ALPHA-LACTALBUMIN
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DOI：
10.1002/j.1460-2075.1994.tb06618.x
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发表时间：
1994-07-01
期刊：
影响因子：
11.4
通讯作者：
HARTL, FU
中科院分区：
文献类型：
--
作者：
HAYERHARTL, MK;EWBANK, JJ;HARTL, FU
伴侣蛋白GroEL结合未折叠的多肽，防止聚集，然后在ATP依赖性过程中介导它们的折叠。为了理解GroEL识别的非天然多肽的结构特征，我们使用α-乳白蛋白（α LA）作为模型底物。α LA（14.2 kDa）通过四个二硫键和一个结合的Ca 2+离子稳定，提供了在天然状态和完全未折叠状态之间捕获部分折叠的二硫键中间体的可能性。对GroEL具有高亲和力的α LA的构象异构体是紧凑的，含有多达三个二硫键，并且具有显著的二级结构，但缺乏稳定的三级结构并且暴露疏水表面。复合物的形成需要几乎完整的α LA序列，并且强烈依赖于稳定疏水相互作用的盐。α LA展开为延伸状态以及在形成有序三级结构后疏水表面的掩埋阻止与GroEL的结合。有趣的是，GroEL仅与α LA的许多部分折叠的二硫键中间体的特定子集相互作用，因此可能影响体外折叠途径的动力学，导致与天然组合形成二硫键。我们的结论是，伴侣蛋白相互作用的疏水表面暴露的蛋白质在一个灵活的紧凑的中间或熔融球状态。
The chaperonin GroEL binds unfolded polypeptides, preventing aggregation, and then mediates their folding in an ATP-dependent process. To understand the structural features in non-native polypeptides recognized by GroEL, we have used alpha-lactalbumin (alpha LA) as a model substrate. alpha LA (14.2 kDa) is stabilized by four disulfide bonds and a bound Ca2+ ion, offering the possibility of trapping partially folded disulfide intermediates between the native and the fully unfolded state. The conformers of alpha LA with high affinity for GroEL are compact, containing up to three disulfide bonds, and have significant secondary structure, but lack stable tertiary structure and expose hydrophobic surfaces. Complex formation requires almost the complete alpha LA sequence and is strongly dependent on salts that stabilize hydrophobic interactions. Unfolding of alpha LA to an extended state as well as the burial of hydrophobic surface upon formation of ordered tertiary structure prevent the binding to GroEL. Interestingly, GroEL interacts only with a specific subset of the many partially folded disulfide intermediates of alpha LA and thus may influence in vitro the kinetics of the folding pathways that lead to disulfide bonds with native combinations. We conclude that the chaperonin interacts with the hydrophobic surfaces exposed by proteins in a flexible compact intermediate or molten globule state.