Publication details
Conformational Entropy from Slowly Relaxing Local Structure Analysis of N-15-H Relaxation in Proteins: Application to Pheromone Binding to MUP-I in the 283-308 K Temperature Range
| Authors | |
|---|---|
| Year of publication | 2017 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Physical Chemistry B |
| MU Faculty or unit | |
| Citation | |
| Web | http://pubs.acs.org/doi/abs/10.1021/acs.jpcb.7b06049 |
| Doi | http://dx.doi.org/10.1021/acs.jpcb.7b06049 |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | MODEL-FREE APPROACH; MAGNETIC-RESONANCE RELAXATION; NMR RELAXATION; BACKBONE DYNAMICS; LIGAND-BINDING; ORDER PARAMETERS; DEPENDENCE; COMPLEX; DOMAIN; MOTIONS |
| Description | The slowly relaxing local structure (SRLS) approach is applied to N-15-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, tau(1,0) and locally with correlation time, tau(2,0), where tau(1,0) >> tau(2,0). The local motion is restricted by the potential u =-c(0)(2)D(00)(2), where D-00(2) is the Wigner rotation matrix element for L = 2, K = 0, and c(0)(2) evaluates the strength of the potential. u yields straightforwardly the order parameter, < D-00(2)>, and the conformational entropy, S-k, both given by P-eq = exp(-u). The deviation of the local ordering/local diffusion axis from the N-H bond, given by the angle beta, is also determined. We find that c(0)(2) congruent to 18 +/- 4 and T-2,T-0 = 0-170 ps for ligand-free MUP-I, whereas c(0)(2) congruent to 15 +/- 4 and tau(2,0) = 20-270 ps for ligand-bound MUP-I beta is in the 0-10 degrees range. c(0)(2) and tau(2,0) decrease, whereas beta increases, when the temperature is increased from 283 to 308 K. Thus, SRLS provides physically well-defined structure-related (c(0)(2) and < D-00 >(2)), motion-related (tau(2,0)), geometry related (beta), and binding-related (S-k) 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-2) and rate (tau(e)) of the local motion, and a phenomenological exchange term (R-ex). S-2 is found to decrease (implying implicitly "global" increase in S-k) upon pheromone binding. |