Protein dynamical transition at 110 K

Abstract

Proteins are known to undergo a dynamical transition at around 200 K but the underlying mechanism, physical origin, and relationship to water are controversial. Here we report an observation of a protein dynamical transition as low as 110 K. This unexpected protein dynamical transition precisely correlated with the cryogenic phase transition of water from a high-density amorphous to a low-density amorphous state. The results suggest that the cryogenic protein dynamical transition might be directly related to the two liquid forms of water proposed at cryogenic temperatures.conformation fluctuations | water phase transition | high-pressure cryocooling | X-ray crystallography I t is known that a hydrated protein undergoes a dynamical transition at around 200 K (1). Proteins below the transition temperature are in a glassy state with little conformational flexibility and no appreciable biological function; above the transition temperature flexibility is restored and the protein becomes biologically active (2-4). This protein dynamical transition has been extensively studied by measuring the mean square atomic displacement, hx 2 i, of protein atoms as a function of temperature with various methods, including Mössbauer and terahertz time domain spectroscopies (5-7), X-ray crystallography (4, 8-11), neutron scattering (2,(12)(13)(14)(15)(16)(17)(18)(19), and molecular dynamics simulations (20)(21)(22)(23)(24)(25).It is believed that the protein dynamical transition involves a strong coupling to the hydration water (10,26,27), as a protein dehydrated below a critical level (water/protein mass ratio of ∼0.2) does not show the dynamical transition (13,14,28). Several mechanisms have been proposed to explain the microscopic origin of protein dynamical transition, including α and β fluctuations in the bulk solvent and the hydration shell (29, 30), liquid-glass transition of hydration water (31), a frequency window scenario (32, 33), and a fragile to strong transition of the hydration water (15,20).In this work, we studied a protein dynamical transition inside protein crystals using a high-pressure cryocooling method (34) and temperature-dependent X-ray diffraction (8,35,36). Protein crystals contain large amounts of water in solvent channels between the proteins in the crystal lattice; water fractions of greater than 50% are very common. It has been reported that this intracrystalline water can be cryocooled under high pressure into a high-density amorphous (HDA) state that subsequently transforms upon heating to the low-density amorphous (LDA) (36) water typical of ambient-pressure flash-cooling [in bulk water the respective densities of HDA and LDA are 1.17 and 0.94 g cm −3 at 77 K and 0.1 MPa. (37, 38)]. In this study, the temperature of the HDA-LDA transition was adjusted by controlling solvent conditions inside the protein crystals. X-ray diffraction data from five thaumatin crystals were used for this study, including four high-pressure cryocooled crystals (Thau-0M-1, Thau-0M-2, Thau-0.45M, Thau-0.9M; 0.9M indicates w...

Glass polymorphism and liquid–liquid phase transition in aqueous solutions: experiments and computer simulations

“…248 This finding is striking, as such transitions have previously been observed only around 180-240 K. 284,285 Interestingly, at 110 K also the polyamorphic transition of solvent water occurs. 248,281 However, when avoiding the formation of HDA-type hydration water by cooling an identical protein crystal at ambient pressure, no increase in protein mobility is visible up to 180-240 K. Thus, it seems that the HDA -LDA transition in pressure-vitrified hydration water is accountable for the protein dynamical transition at cryogenic temperatures, whereas the mobility in LDA-type hydration water is not sufficient to trigger the transition at 110 K. One could speculate that this results from the water molecules being more mobile in the HDA than in the LDA state. Indeed, it has been shown that the dynamics in HDA near 110 K are two orders of magnitude faster than in LDA, 286 reaching the relaxation times of an ultraviscous liquid.…”

“…In particular this change in glycerol conformation is observed concomitantly with the polyamorphic transition, suggesting that water polyamorphism may also affect the structure and dynamics of solutes (e.g., alcohols, polymers, proteins [247][248][249][250][251][252] ).…”

“…While not accessible in bulk water the FSDC at ambient pressure was inferred for protein hydration water. 247,249,250 Going beyond this dynamic transition, the work by Kim et al 248,[277][278][279][280][281] tackles structural transformations induced by pressure. When rapidly cooling a pressurized (E0.2 GPa) protein crystal, ice formation can be entirely avoided as indicated by X-ray studies.…”

Effect of water polyamorphism on the molecular vibrations of glycerol in its glassy aqueous solutions

“…Now, considering that the structure of water around a macromolecule plays the important roles in the structural stability and the functional expression of the macromolecule, [74][75][76] it is worthwhile to rethink the behaviors of aqueous solutions from a viewpoint of water polyamorphism. 32,66,68,[77][78][79][80][81][82] Recently, it has been proposed that the polyamorphic transition of solvent water may affect the protein dynamics, for example, the effect of the fragile-to-strong crossover of water on the softening of protein around 220 K [83][84][85] and the relationship between the high-to low-density transition of amorphous ice confined in the protein crystal and the protein dynamical transition around 110 K. 86 However, these experiments were performed using the confined water and the direct interrelationship between the polyamorphic behavior of "bulk" solvent water and the dynamics of solute is unclear. In this study, we showed for the first time that the polyamorphic transition of bulk solvent water affects the molecular vibrations of glycerol directly.…”

Anomalous Freezing of Nano‐Confined Water in Room‐Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Nitrate

“…[16,17] In relation to proteins, HDA ice and LDA ice have ag reat impact on bioengineering. [18,19] Crystal ice in biomolecules is as ignificant barrier in the field of cryopreservation.U sing X-ray diffraction, HDA to LDA phase transition under high-pressurec ryocooling has been observed and was accompanied by protein structural relaxation. MD simulations of lysozyme and hydration water was carried out to demonstrate ap rotein glass transition.…”