Evolution of the Internal Dynamics of Two Globular Proteins from Dry Powder to Solution

Abstract

Myoglobin and lysozyme picosecond internal dynamics in solution is compared to that in hydrated powders by quasielastic incoherent neutron scattering. This technique is sensitive to the motions of the nonexchangeable hydrogen atoms in a sample. Because these are homogeneously distributed throughout the protein structure, the average dynamics of the protein is described. We first propose an original data treatment to deal with the protein global motions in the case of solution samples. The validity of this treatment is checked by comparison with classical measurements of the diffusion constants. The evolution with the scattering vector of the width and relative contribution of the quasielastic component was then used to derive information on the amount of local diffusive motions and their characteristic average relaxation time. From dry powder to coverage by one water layer, the surface side chains progressively acquire the possibility to diffuse locally. On subsequent hydration, the main effect of water is to improve the rate of these diffusive motions. Motions with higher average amplitude occur in solution, about three times more than for a hydrated powder at complete coverage, with a shorter average relaxation time, approximately 4.5 ps compared to 9.4 ps for one water monolayer.

Protein self-diffusion in crowded solutions

“…j l ðxÞ is the lth-order spherical Bessel function of first kind. It was found (24,25) and reproduced in our study that a single Lorentzian line shape with HWHM γ and amplitude α approximates the calculated scattering function S tþr ðQ;ωÞ for rotational and translational diffusion inside error bars in the Q-range relevant for our experiment. For given D t and D r , which are Q-independent, the Q-dependence of dðQÞ can be discussed.…”

“…For finite Q, dðQÞ monotonously increases with Q and converges rapidly to a constant value. By the limit D ¼ lim Q→∞ dðQÞ; [17] we define the observable diffusion coefficient D. The rapid convergence of dðQÞ restates the simple diffusive relation γðQÞ ¼ DQ 2 as observed in the accessible Q-range, as found already numerically (24,25). Rotational diffusion thus acts as an additional contribution not distinguishable from translational diffusion without careful modeling and approximations.…”

“…The width of the two Lorentzians L γ and L Γ represent the time scales of two separated spectral components: while the broader width Γ accounts for fast internal and interdomain motions within the protein, γ is attributed to the convolution of the translational and rotational diffusion of the entire protein (24,25,30,32). The widths γ as obtained from the fits Eq.…”

“…Recent neutron scattering work studied protein dynamics in solutions, thereby mainly addressing the hydration and temperature dependence of internal motions (24)(25)(26)(27)(28)(29). Few studies, however, investigated protein short-time diffusion (30)(31)(32)(33) or longtime diffusion (34)(35)(36).…”

Temperature and timescale dependence of protein dynamics in methanol : water mixtures

“…24 Neutron scattering experiments have shown protein dynamical amplitudes to increase upon hydration. [25][26][27] One possibility is that, in the absence of water, protein sidechains form hydrogen bonds with each other thus rigidifying the protein. Upon hydration, some of these hydrogen bonds would be transferred to water molecules, with the effect that the sidechains diffuse more freely in the solvent.…”