Mande S C, Sobhia M E
Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India.
Protein Eng. 2000 Feb;13(2):133-41. doi: 10.1093/protein/13.2.133.
A variety of physico-chemical methods employ chemical denaturants to unfold proteins, and study different biophysical processes involved therein. Chemical denaturants are believed to induce unfolding by stabilizing the unfolded state of proteins over the folded state, either macroscopically or through specific interactions. In order to characterize the nature of specific interactions between proteins and denaturants, we have solved crystal structures of hen egg-white lysozyme complexed with denaturants, and report here dimethyl sulfoxide and guanidinium chloride complexes. The dimethyl sulfoxide molecules and guanidinium ions were seen to bind the protein at specific sites and were involved in characteristic interactions. They share a major binding site between them, the C site in the sugar binding cleft of the enzyme. Although the overall conformations of the complexes were very similar to the native structure, spectacular conformational changes were seen to occur locally. Temperature factors were also seen to drop dramatically in the local regions close to the denaturant binding sites. An interesting observation of the present study was the generation of a sodium ion binding site in hen egg-white lysozyme in the presence of denaturants, which was hitherto unknown in any of the other lysozyme structures solved so far. Loss of some of the crucial side chain-main chain interactions may form the initial events in lysozyme unfolding.
多种物理化学方法利用化学变性剂使蛋白质展开，并研究其中涉及的不同生物物理过程。化学变性剂被认为是通过在宏观上或通过特定相互作用使蛋白质的未折叠状态比折叠状态更稳定来诱导展开。为了表征蛋白质与变性剂之间特定相互作用的性质，我们解析了与变性剂复合的鸡蛋清溶菌酶的晶体结构，并在此报告二甲基亚砜和氯化胍复合物。二甲基亚砜分子和胍离子在特定位点与蛋白质结合，并参与特征性相互作用。它们在酶的糖结合裂隙中的C位点共享一个主要结合位点。尽管复合物的整体构象与天然结构非常相似，但在局部区域观察到了显著的构象变化。在靠近变性剂结合位点的局部区域，温度因子也显著下降。本研究一个有趣的发现是，在有变性剂存在的情况下，鸡蛋清溶菌酶中产生了一个钠离子结合位点，这在迄今为止解析的任何其他溶菌酶结构中都是未知的。一些关键的侧链-主链相互作用的丧失可能是溶菌酶展开的初始事件。
