Kato Hidenori, Vu Ngoc Diep, Feng Hanqiao, Zhou Zheng, Bai Yawen
Laboratory of Biochemistry, Center for Cancer Research, National Cancer Institute, Building 37, Room 6114E, Bethesda, MD 20892, USA.
J Mol Biol. 2007 Jan 19;365(3):881-91. doi: 10.1016/j.jmb.2006.10.048. Epub 2006 Oct 21.
T4 lysozyme has two easily distinguishable but energetically coupled domains: the N and C-terminal domains. In earlier studies, an amide hydrogen/deuterium exchange pulse-labeling experiment detected a stable submillisecond intermediate that accumulates before the rate-limiting transition state. It involves the formation of structures in both the N and C-terminal regions. However, a native-state hydrogen exchange experiment subsequently detected an equilibrium intermediate that only involves the formation of the C-terminal domain. Here, using stopped-flow circular dichroism and fluorescence, amide hydrogen exchange-folding competition, and protein engineering methods, we re-examined the folding pathway of T4-lysozyme. We found no evidence for the existence of a stable folding intermediate before the rate-limiting transition state at neutral pH. In addition, using native-state hydrogen exchange-directed protein engineering, we created a mimic of the equilibrium intermediate. We found that the intermediate mimic folds with the same rate as the wild-type protein, suggesting that the equilibrium intermediate is an on-pathway intermediate that exists after the rate-limiting transition state.
T4溶菌酶有两个易于区分但在能量上相互耦合的结构域:N端和C端结构域。在早期研究中,一项酰胺氢/氘交换脉冲标记实验检测到一个稳定的亚毫秒级中间体,它在限速过渡态之前积累。它涉及N端和C端区域结构的形成。然而,随后的一项天然态氢交换实验检测到一个仅涉及C端结构域形成的平衡中间体。在此,我们使用停流圆二色性和荧光、酰胺氢交换折叠竞争以及蛋白质工程方法,重新审视了T4溶菌酶的折叠途径。我们发现在中性pH条件下,没有证据表明在限速过渡态之前存在稳定的折叠中间体。此外,通过天然态氢交换导向的蛋白质工程,我们创建了一个平衡中间体的模拟物。我们发现该中间体模拟物与野生型蛋白质以相同的速率折叠,这表明平衡中间体是限速过渡态之后存在的一条折叠途径上的中间体。