Gloss L M, Matthews C R
Department of Chemistry, Center for Biomolecular Structure and Function, Pennsylvania State University, University Park 16802, USA.
Biochemistry. 1998 Nov 10;37(45):16000-10. doi: 10.1021/bi981694f.
The kinetic folding mechanism of the isolated dimerization domain of E. coli Trp repressor, [2-66]2 TR, consists of a nearly diffusion-limited association reaction to form a dimeric intermediate, I2, which is then converted to the native, folded dimeric species, N2 by a first-order folding step (preceding paper in this issue). The two transition states traversed in the folding of [2-66]2 TR were characterized by monitoring the folding and unfolding reactions by stopped-flow fluorescence as a function of temperature and urea. For both transition states, the barriers are dominated by the enthalpic component; the entropic component accelerates the association reaction but has little effect on the subsequent rearrangement reaction. The transition state between I2 and N2 is relatively nativelike, as determined by the sensitivity of the rate constants to denaturant. This study also highlights the key role of solvent entropy in determining the magnitude of the relative free energy of the transition states and the ground states. The positive entropy change for the I2 to N2 reaction, presumably arising from the release of solvent from hydrophobic surfaces, is the driving force for this final folding step, offsetting an unfavorable enthalpic term.
大肠杆菌色氨酸阻遏物[2 - 66]2 TR分离的二聚化结构域的动力学折叠机制，包括一个接近扩散极限的缔合反应以形成二聚体中间体I2，随后通过一级折叠步骤将其转化为天然的、折叠的二聚体形式N2（本期之前的论文）。通过监测[2 - 66]2 TR折叠和解折叠反应的停流荧光随温度和尿素的变化，对折叠过程中经历的两个过渡态进行了表征。对于这两个过渡态，能垒主要由焓成分主导；熵成分加速了缔合反应，但对随后的重排反应影响很小。由速率常数对变性剂的敏感性可知，I2和N2之间的过渡态相对类似天然态。该研究还强调了溶剂熵在决定过渡态和基态相对自由能大小方面的关键作用。I2到N2反应的正熵变大概源于疏水表面溶剂的释放，是这一最终折叠步骤的驱动力，抵消了不利的焓项。
