Central European Institute of Technology, Masaryk University , Kamenice 5, 62500 Brno, Czech Republic.
National Center for Biomolecular Research, Faculty of Science, Masaryk University , Kamenice 5, 62500 Brno, Czech Republic.
J Phys Chem B. 2017 Sep 21;121(37):8684-8692. doi: 10.1021/acs.jpcb.7b06049. Epub 2017 Sep 8.
The slowly relaxing local structure (SRLS) approach is applied to N-H relaxation from the major urinary protein I (MUP-I), and its complex with pheromone 2-sec-butyl-4,5-dihydrothiazol. The objective is to elucidate dynamics, and binding-induced changes in conformational entropy. Experimental data acquired previously in the 283-308 K temperature range are used. The N-H bond is found to reorient globally with correlation time, τ, and locally with correlation time, τ, where τ ≫ τ. The local motion is restricted by the potential u = -cD, where D is the Wigner rotation matrix element for L = 2, K = 0, and c evaluates the strength of the potential. u yields straightforwardly the order parameter, ⟨D⟩, and the conformational entropy, S, both given by P = exp(-u). The deviation of the local ordering/local diffusion axis from the N-H bond, given by the angle β, is also determined. We find that c ≅ 18 ± 4 and τ = 0-170 ps for ligand-free MUP-I, whereas c ≅ 15 ± 4 and τ = 20-270 ps for ligand-bound MUP-I. β is in the 0-10° range. c and τ decrease, whereas β increases, when the temperature is increased from 283 to 308 K. Thus, SRLS provides physically well-defined structure-related (c and ⟨D⟩), motion-related (τ), geometry-related (β), and binding-related (S) local parameters, and their temperature-dependences. Intriguingly, upon pheromone binding the conformational entropy of MUP-I decreases at high temperature and increases at low temperature. The very same experimental data were analyzed previously with the model-free (MF) method which yielded "global" (in this context, "relating to the entire 283-308 K range") amplitude (S) and rate (τ) of the local motion, and a phenomenological exchange term (R). S is found to decrease (implying implicitly "global" increase in S) upon pheromone binding.
缓慢弛豫局部结构 (SRLS) 方法应用于主要尿蛋白 I (MUP-I) 和其与信息素 2-丁基-4,5-二氢噻唑的复合物的 N-H 弛豫。目的是阐明动力学和构象熵的结合诱导变化。先前在 283-308 K 温度范围内获得的实验数据用于该研究。发现 N-H 键与相关时间 τ 全局重新取向，并且与相关时间 τ 局部重新取向，其中 τ ≫ τ。局部运动受到势 u = -cD 的限制，其中 D 是 L = 2、K = 0 的 Wigner 旋转矩阵元，而 c 评估势的强度。u 直接给出序参量 ⟨D⟩和构象熵 S，两者均由 P = exp(-u) 给出。通过角度 β 确定局部排序/局部扩散轴与 N-H 键的偏离，β 由角度 β 确定。我们发现，配体游离 MUP-I 的 c ≅ 18 ± 4 和 τ = 0-170 ps，而配体结合 MUP-I 的 c ≅ 15 ± 4 和 τ = 20-270 ps。β 在 0-10°范围内。当温度从 283 升高到 308 K 时，c 和 τ 减小，而 β 增加。因此，SRLS 提供了物理上定义良好的结构相关 (c 和 ⟨D⟩)、运动相关 (τ)、几何相关 (β) 和结合相关 (S) 的局部参数及其温度依赖性。有趣的是，在信息素结合后，MUP-I 的构象熵在高温下降低，在低温下增加。以前使用无模型 (MF) 方法对相同的实验数据进行了分析，该方法产生了局部运动的“全局”(在这种情况下，“与整个 283-308 K 范围相关”)幅度 (S) 和速率 (τ)，以及唯象交换项 (R)。发现信息素结合后 S 减小(隐含地暗示“全局”S 增加)。
