Gervasoni P, Staudenmann W, James P, Gehrig P, Plückthun A
Biochemisches Institut, Universität Zürich, Switzerland.
Proc Natl Acad Sci U S A. 1996 Oct 29;93(22):12189-94. doi: 10.1073/pnas.93.22.12189.
Escherichia coli RTEM beta-lactamase reversibly forms a stable complex with GroEL, devoid of any enzymatic activity, at 48 degrees C. When beta-lactamase is diluted from this complex into denaturant solution, its unfolding rate is identical to that from the native state, while the unfolding rate from the molten globule state is too fast to be measured. Electrospray mass spectrometry shows that the rate of proton exchange in beta-lactamase in the complex at 48 degrees C is slower than in the absence of GroEL at the same temperature, and resembles the exchange of the native state at 25 degrees C. Similarly, the final number of protected deuterons is higher in the presence of GroEL than in its absence. We conclude that, for beta-lactamase, a state with significant native structure is bound to GroEL. Thus, different proteins are recognized by GroEL in very different states, ranging from totally unfolded to native-like, and this recognition may depend on which state can provide sufficient accessible hydrophobic amino acids in a suitably clustered arrangement. Reversible binding of native-like states with hydrophobic patches may be an important property of GroEL to protect the cell from aggregating protein after heat-shock.
大肠杆菌RTEMβ-内酰胺酶在48摄氏度时与GroEL可逆地形成一种稳定的复合物，且没有任何酶活性。当β-内酰胺酶从这种复合物稀释到变性剂溶液中时，其解折叠速率与从天然状态下的解折叠速率相同，而从熔球态的解折叠速率太快以至于无法测量。电喷雾质谱显示，48摄氏度时复合物中的β-内酰胺酶的质子交换速率比相同温度下不存在GroEL时要慢，并且类似于25摄氏度时天然状态的交换。同样，存在GroEL时受保护的氘核的最终数量比不存在时更高。我们得出结论，对于β-内酰胺酶来说，具有显著天然结构的一种状态与GroEL结合。因此，不同的蛋白质在从完全解折叠到类似天然状态的非常不同的状态下被GroEL识别，并且这种识别可能取决于哪种状态能够以适当聚集的排列提供足够数量可接近的疏水氨基酸。具有疏水斑块的类似天然状态的可逆结合可能是GroEL保护细胞免受热休克后蛋白质聚集影响的一个重要特性。
