Electrostatics of the protein-water interface and the dynamical transition in proteins

Abstract

Atomic displacements of hydrated proteins are dominated by phonon vibrations at low temperatures and by dissipative large-amplitude motions at high temperatures. A crossover between the two regimes is known as a dynamical transition. Recent experiments indicate a connection between the dynamical transition and the dielectric response of the hydrated protein. We analyze two mechanisms of the coupling between the protein atomic motions and the protein-water interface. The first mechanism considers viscoelastic changes in the global shape of the protein plasticized by its coupling to the hydration shell. The second mechanism involves modulations of the local motions of partial charges inside the protein by electrostatic fluctuations. The model is used to analyze mean-square displacements of iron of metmyoglobin reported by Mössbauer spectroscopy. We show that high displacement of heme iron at physiological temperatures is dominated by electrostatic fluctuations. Two onsets, one arising from the viscoelastic response and the second from electrostatic fluctuations, are seen in the temperature dependence of the mean-square displacements when the corresponding relaxation times enter the instrumental resolution window.

Non-Gaussian Statistics and Nanosecond Dynamics of Electrostatic Fluctuations Affecting Optical Transitions in Proteins

“…We stress here that the actual temperature variation of σ i (T) 2 will not follow a linear dependence as drawn by the solid line in Figure 5, but will deviate from it at the point of glass transition when the collective (nanosecond at ≃300 K) motions of the interface become sufficiently slow to cross the experimental observation window. 54 Their kinetic arrest is expected at this glass-transition temperature T g > T 0 , with the restoration of the linear response σ i (T) 2 ≃ 2k B Tλ St at the crossover (shown by the dash-dotted line in Figure 5). This qualitative picture seems to be followed by the low-temperature portion of σ 0 (T) 2 from simulations ( Figure 5), although with a slope higher than the estimate from λ St at 300 K. The difference is attributed to a finite trajectory length in simulations, similar to the effect of cooling rate in the laboratory glass transition.…”

Protein electron transfer: Dynamics and statistics

“…In addition, when the overall spectral density is split into the water and protein components, their corresponding low-frequency peaks point to nearly equal relaxation times. 45,79 This observation indicates that the protein and water motions contributing to the low-frequency relaxation are strongly coupled. These nuclear modes are specific to the elastically soft hydrated protein.…”

“…45 In the former case, the energy gap coordinate corresponds to changing the oxidation state of the iron of the heme, in the latter case the energy gap is between the ground and excited singlets of GFP's chromophore. The characteristic feature of several such functions reported so far 30,45,79 is the existence of two peaks, with a possibility that even slower relaxation times are still not resolved on the length of the simulation trajectory. 30 and green fluorescent proteins (GFP) 45 obtained from MD simulations.…”

“…The rate constant then follows the Arrhenius law. On the contrary, the entrance of slow elastic motions of the proteins into the observation window 79 at higher temperatures implies a faster than linear growth of σ (T) 2 [ Fig. (8)].…”

Understanding the decay of proteins: A method to study time dependent response of pM concentration of insulin at microwave frequencies

“…Response of biomolecules in buffer is central in understanding the behaviour of biological systems in their native ecological conditions [1], [2], [3], [4], [5], because most of the biological systems such as proteins are active in aqua medium, and they are found to closely mimic their natural behaviour in a buffer medium in vivo . Due to this protein solutions are prepared in buffer at high concentration preferably greater than 1 mg/ml for storage.…”