Puzzle of Protein Dynamical Transition

Abstract

Despite recent extensive efforts, the nature of the dynamics of biological macromolecules still remains unclear. In particular, contradicting models have been proposed for explaining the temperature behavior of the mean square displacement, MSD, and of the system relaxation time, τ. To solve this puzzle, different neutron scattering experiments with different instrumental energy resolutions were performed on dry and hydrated lysozyme. The obtained results show that the so called dynamical transition: (i) is a finite instrumental energy resolution effect, and more specifically, it appears when the characteristic system relaxation time intersects the resolution time, (ii) it does not imply any transition in the dynamical properties of the systems, (iii) it is not due to the fragile-to-strong dynamical crossover (FSC) in the temperature behavior of the system relaxation time, differently to what S. H. Chen et al. proposed [Proc. Natl. Acad. Sci. U.S.A.2006, 103, 9012]. Furthermore, the obtained results confirm the change in the τ-temperature dependence at T = 220 K of S. H. Chen et al., and show that it is not due to finite instrumental energy resolution effects and it is not connected to numerical errors in the data analysis protocol, differently to what W. Doster et al. proposed [Phys. Rev. Lett.2010, 104, 098101].

Hydration-dependent dynamic crossover phenomenon in protein hydration water

“…This conjecture is under debate [16,19,27,28]. It is well known that most of proteins only function with sufficient hydration water.…”

“…[12] is due to numerical errors in the data analysis protocol and can be ruled out with an improved analysis method. Magazù et al [16] and Schirò et al [19] draw opposite conclusions on the role that the dynamic crossover plays in the onset of the PDT with resolution-dependent neutron scattering experiments. Swenson et al [14], Pawlus et al [15], and Fenimore et al [18] propose that the appearance of the dynamic crossover in the hydration water is due to the existences of two different relaxation processes, the structural relaxation and a secondary relaxation, rather than a qualitative * Corresponding author: sowhsin@mit.edu change from an Arrhenius behavior to a super-Arrhenius behavior of the structural relaxation time.…”

“…This phenomenon is of particular interest, partially because (i) the crossover temperature T X of the hydration water is close to the transition temperature of the so-called protein dynamic transition (PDT) [13] T D and thus it is conjectured that the PDT is induced by the dynamic crossover of the hydration water [12] and (ii) this crossover is interpreted as an anomalous feature of the structural relaxation of the hydration water and is ascribed to the existence of the high-density liquid and low-density liquid phases in the supercooled water [12]. To date, this phenomenon and its physical implications are still largely debated [14][15][16][17][18][19]. Doster et al [17] state that the crossover observed in Ref.…”

Dynamical and orientational structural crossovers in low-temperature glycerol

“…It is followed by one or two lowtemperature crossovers and, finally, with a much stronger increase above the temperature of the dynamical transition T d ∼ 200 − 250 K [13]. This latter temperature depends on a number of factors, including the resolution of the spectrometer, i.e., effectively the time period over which the atomic displacements are recorded [14,15]. This phenomenology has attracted significant attention since enhanced flexibility and, therefore, the ability to perform biological function can develop at T > T d [16].…”

Intrinsic mean-square displacements in proteins

“…Following pioneering experiments and subsequent developments, the mean square displacement (MSD) of hydrogen in proteins can now be readily observed in neutron scattering experiments [1][2][3][4][5][6][7][8][9][10][11]. Specifically, the global average MSD of H throughout the protein is typically determined from the elastic component of the incoherent dynamic structure factor (DSF).…”