Puzzle of Protein Dynamical Transition (original) (raw)
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Dynamic Transition Associated with the Thermal Denaturation of a Small Beta Protein
Biophysical Journal, 2002
We studied the temperature dependence of the picosecond internal dynamics of an all- protein, neocarzinostatin, by incoherent quasielastic neutron scattering. Measurements were made between 20°C and 71°C in heavy water solution. At 20°C, only 33% of the nonexchanged hydrogen atoms show detectable dynamics, a number very close to the fraction of protons involved in the side chains of random coil structures, therefore suggesting a rigid structure in which the only detectable diffusive movements are those involving the side chains of random coil structures. At 61.8°C, although the protein structure is still native, slight dynamic changes are detected that could reflect enhanced backbone and -sheet side-chain motions at this higher temperature. Conversely, all internal dynamics parameters (amplitude of diffusive motions, fraction of immobile scatterers, mean-squared vibration amplitude) rapidly change during heat-induced unfolding, indicating a major loss of rigidity of the -sandwich structure. The number of protons with diffusive motion increases markedly, whereas the volume occupied by the diffusive motion of protons is reduced. At the half-transition temperature (T ϭ 71°C) most of backbone and -sheet side-chain hydrogen atoms are involved in picosecond dynamics.
Dynamics of proteins at low temperatures: fibrous vs. globular
Applied Physics A: Materials Science & Processing, 2002
We have measured quasielastic neutron scattering from H 2 O-hydrated collagen and haemoglobin at T ≤ 270 K. The data consist of sets of nearly elastic peaks showing (i) Q,T -dependent decreases in window-integrated intensities S qe (Q;T ) proportional to effective Debye-Waller factors and (ii) small line-shape changes due to various types of proton motions with ns > τ > 10 ps. Relative to haemoglobin, the 200-K dynamic transition is shifted upward by 20-25 K in collagen, and the T -dependence of m.-sq. displacements derived from S qe (Q;T ) suggests that in triple-helical systems there are three rather than two regimes: one up to around 120 K (probably purely harmonic), an intermediate quasiharmonic region with a linear dependence up to ≈ 240 K, followed by a steeper nonlinear rise similar to that in globular proteins.
The ‘glass transition’ in protein dynamics: what it is, why it occurs, and how to exploit it
Biophysical Chemistry, 2003
All proteins undergo a dramatic change in their dynamical properties at approximately 200 K. Above this temperature, their dynamic behavior is dominated by large-scale collective motions of bonded and nonbonded groups of atoms. At lower temperatures, simple harmonic vibrations predominate. The transition has been described as a 'glass transition' to emphasize certain similarities between the change in dynamic behavior of individual protein molecules and the changes in viscosity and other properties of liquids when they form a glass. The glass transition may reflect the intrinsic temperature dependence of the motions of atoms in the protein itself, in the bound solvent on the surface of the protein, or it may reflect contributions from both. Protein function is significantly altered below this transition temperature; a fact that can be exploited to trap normally unstable intermediates in enzyme-catalyzed reactions and stabilize them for periods long enough to permit their characterization by high-resolution protein crystallography.
The Journal of Physical Chemistry B, 2012
Mössbauer spectroscopy and neutron scattering measurements on proteins embedded in solvents including water and aqueous mixtures have emphasized the observation of the distinctive temperature dependence of the atomic mean square displacements, u 2 , commonly referred to as the dynamic transition at some temperature T d. At low temperatures, u 2 increases slowly, but it assumes stronger temperature dependence after crossing T d , which depends on the time/frequency resolution of the spectrometer. Various authors have made connection of the dynamics of solvated proteins including the dynamic transition to that of glass-forming substances. Notwithstanding, no connection is made to the similar change of temperature dependence of u 2 obtained by quasielastic neutron scattering when crossing the glass transition temperature T g , generally observed in inorganic, organic and polymeric glass-formers. Evidences are presented here to show that such change of the temperature dependence of u 2 from neutron scattering at T g is present in hydrated or solvated proteins, as well as in the solvent used, unsurprisingly since the latter is just another organic glass-former. If unaware of the existence of such crossover of u 2 at T g , and if present, it can be mistaken as the dynamic transition at T d with the ill consequences of underestimating T d by the lower value T g , and confusing the identification of the origin of the dynamic transition. The u 2 obtained by neutron scattering at not so low temperatures has contributions from the dissipation of molecules while caged by the anharmonic intermolecular potential at times before dissolution of cages by the onset of the Johari-Goldstein-relaxation or of the merged α-β relaxation. The universal change of u 2 at T g of glassformers, independent of the spectrometer resolution, had been rationalized by sensitivity to change in volume and entropy of the dissipation of the caged molecules and its contribution to u 2. The same rationalization applies to hydrated and solvated proteins for the observed change of u 2 at T g .
A unified model of protein dynamics
Proceedings of the National Academy of Sciences, 2009
Protein functions require conformational motions. We show here that the dominant conformational motions are slaved by the hydration shell and the bulk solvent. The protein contributes the structure necessary for function. We formulate a model that is based on experiments, insights from the physics of glass-forming liquids, and the concepts of a hierarchically organized energy landscape. To explore the effect of external fluctuations on protein dynamics, we measure the fluctuations in the bulk solvent and the hydration shell with broadband dielectric spectroscopy and compare them with internal fluctuations measured with the Mössbauer effect and neutron scattering. The result is clear. Large-scale protein motions are slaved to the fluctuations in the bulk solvent. They are controlled by the solvent viscosity, and are absent in a solid environment. Internal protein motions are slaved to the beta fluctuations of the hydration shell, are controlled by hydration, and are absent in a dehyd...
The Inverse Relationship between Protein Dynamics and Thermal Stability
Biophysical Journal, 2001
Protein powders that are dehydrated or mixed with a glassy compound are known to have improved thermal stability. We present elastic and quasielastic neutron scattering measurements of the global dynamics of lysozyme and ribonuclease A powders. In the absence of solvation water, both protein powders exhibit largely harmonic motions on the timescale of the measurements. Upon partial hydration, quasielastic scattering indicative of relaxational processes appears at sufficiently high temperature. When the scattering spectrum are analyzed with the Kohlrausch-Williams-Watts formalism, the exponent  decreases with increasing temperature, suggesting that multiple relaxation modes are emerging. When lysozyme was mixed with glycerol, its  values were higher than the hydrated sample at comparable temperatures, reflecting the viscosity and stabilizing effects of glycerol.