Temperature Dependence of the Heat Diffusivity of Proteins

Abstract

In a combined experimental-theoretical study, we investigated the transport of vibrational energy from the surrounding solvent into the interior of a heme protein, the sperm whale myoglobin double mutant L29W-S108L, and its dependence on temperature from 20 to 70 K. The hindered libration of a CO molecule that is not covalently bound to any part of the protein but is trapped in one of its binding pockets (the Xe4 pocket) was used as the local thermometer. Energy was deposited into the solvent by IR excitation. Experimentally, the energy transfer rate increased from (30 ps)−1 at 20 K to (8 ps)−1 at 70 K. This temperature trend is opposite to what is expected, assuming that the mechanism of heat transport is similar to that in glasses. In order to elucidate the mechanism and its temperature dependence, nonequilibrium molecular dynamics (MD) simulations were performed, which, however, predicted an essentially temperature-independent rate of vibrational energy flow. We tentatively conclude that the MD potentials overestimate the coupling between the protein and the CO molecule, which appears to be the rate-limiting step in the real system at low temperatures. Assuming that this coupling is anharmonic in nature, the observed temperature trend can readily be explained. In a combined experimental-theoretical study, we investigated the transport of vibrational energy from the surrounding solvent into the interior of a heme-protein, the sperm whale myoglobin double mutant L29W-S108L, in dependence of temperature from 20 K to 70 K. The hindered libration of a CO molecule that is not covalently bound to any part of the protein but is trapped in one of its binding pockets (the Xe4 pocket), was used as "local thermometer". Energy was deposited into the solvent by IR excitation. Experimentally, the energy transfer rate increased from (30 ps) −1 at 20 K to (8 ps) −1 at 70 K. This temperature trend is opposite to what is expected, assuming the mechanism of heat transport is similar to that in glasses. In order to elucidate the mechanism and its temperature dependence, non-equilibrium molecular dynamics (MD) simulations were performed, which, however, predicted an essentially temperature independent rate of vibrational energy flow. We tentatively conclude that the MD potentials overestimate the coupling between the protein and the CO molecule, which appears to be the rate limiting step in the real system at low temperatures. Assuming that this coupling is anharmonic in nature, the observed temperature trend can readily be explained.

Response of Villin Headpiece-Capped Gold Nanoparticles to Ultrafast Laser Heating

“…For 5.7 nm particles used here, a cooling time of 10±5 ps has been reported. 27 That value has been measured for AuNPs in water without capping layer, but what enters in the theory is the thermal conductivity of the surrounding of the AuNP, that is not very different for our capping layer, 61 so the cooling time of the AuNPs per se is of the same order of magnitude. It has been shown (albeit for smaller temperature jumps) 27 that the cooling time is not a function of the size of the temperature jump.…”

Infrared Laser Activation of Soluble and Membrane Protein Assemblies in the Gas Phase

“…CID and continuous IRMPD are 'slow-heating' processes that happen on the time scale longer than intramolecular vibrational redistribution (IVR) of internal energy in the activated ion, in condition of quasiequilibrium of the internal energy and via statistically favourable dissociation pathways with the lowest activation energies. 64 Characteristic IVR times have been measured for proteins in solution and demonstrated to be in the picosecond range, [66][67][68] but, to our knowledge, no gas-phase measurements for intact protein assemblies exist in the literature. Based on our results, we conclude that IVR in protein assemblies happens on a time scale of << 50 ns and defines the observed fragmentation patterns.…”

Vibrational energy flow in the villin headpiece subdomain: Master equation simulations

“…1,[8][9][10][11][12][13][14][15] Pathways for vibrational signaling identified by molecular simulations may overlap pathways along which allosteric transitions occur. 8,11,12,[16][17][18][19][20][21][22][23]75 Time resolved spectroscopies developed to study vibrational energy flow [24][25][26][27][28][29][30][31][32][33][34] have elucidated the nature and rate of energy transport through a number of peptides and proteins. Energy a) dml@unr.edu and stock@physik.uni-freiburg.de flow along helical peptides appears diffusive 30,35,36 with a dependence on temperature that is mediated by interactions with the solvent.…”