beta-Lactamase binds to GroEL in a conformation highly protected against hydrogen/deuterium exchange.

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.

在48℃条件下，大肠杆菌RTEM型β-内酰胺酶（beta-lactamase）可与GroEL可逆结合形成稳定复合物，此时该酶完全丧失酶活性。将该复合物中的β-内酰胺酶稀释至变性剂溶液中时，其解折叠速率与天然状态下的解折叠速率一致；而从熔球态（molten globule）出发的解折叠速率过快，无法测得。电喷雾质谱（Electrospray mass spectrometry）检测结果显示，48℃下复合物中β-内酰胺酶的质子交换速率慢于相同温度下无GroEL存在时的质子交换速率，且与25℃下天然状态的质子交换速率相近。类似地，存在GroEL时，被保护的氘核最终数量高于无GroEL时的水平。据此我们推断，对于β-内酰胺酶而言，与GroEL结合的是具有显著天然结构的构象状态。由此可见，GroEL可识别处于多种不同构象状态的蛋白质，涵盖完全解折叠至类天然构象的全部范围，且这种识别作用可能取决于何种构象状态能够提供足够数量、且以合适方式聚集的可及性疏水氨基酸残基。带有疏水补丁的类天然构象与GroEL的可逆结合，或许是GroEL在热激（heat-shock）后保护细胞免受蛋白质聚集损伤的关键特性之一。