Kim S, Baum J
Joint Graduate Program in Biochemistry, Rutgers-UMDNJ, Piscataway, New Jersey 08854, USA.
Protein Sci. 1998 Sep;7(9):1930-8. doi: 10.1002/pro.5560070908.
alpha-Lactalbumin (alpha-LA) undergoes a pH-dependent unfolding from the native state to a partially unfolded state (the molten globule state). To understand the role of electrostatic interactions in protein denaturation, NMR and CD pH titration experiments are performed on guinea pig alpha-LA. Variation of pH over the range of 7.0 to 2.0 simultaneously leads to the acid denaturation of the protein and the titration of individual ionizable groups. The pH titrations are interpreted in the context of these coupled events, and indicate that acid denaturation in alpha-LA is a cooperative event that is triggered by the protonation of two ionizable residues. Our NMR results suggest that the critical electrostatic interactions that contribute to the denaturation of alpha-LA are concentrated in the calcium binding region of the protein.
α-乳白蛋白(α-LA)会经历从天然状态到部分展开状态(熔球态)的pH依赖性去折叠过程。为了理解静电相互作用在蛋白质变性中的作用,对豚鼠α-LA进行了核磁共振(NMR)和圆二色(CD)pH滴定实验。在7.0至2.0的pH范围内变化会同时导致蛋白质的酸变性以及各个可电离基团的滴定。在这些耦合事件的背景下对pH滴定进行了解释,结果表明α-LA中的酸变性是由两个可电离残基的质子化引发的协同事件。我们的NMR结果表明,促成α-LA变性的关键静电相互作用集中在该蛋白质的钙结合区域。