Protein dynamics An overview on flash‐photolysis over broad temperature ranges

Abstract

Ligand binding kinetics to hemc-proteins between 40 and 300 K point lo a regulatory role of protein dynamics. A protein-specific susccpiibility of the heme-iron reactivity to dynamic fluctuationsemerges from the distribution of reaction enthalpics dcrivcd from flash-photolysis measurcmcnis bciow SI. I80 K; we quantify it in terms of 'intramolecular viscosity'. postulating lhal narrow low-temperature enthulpy distributions correspond to low internal viscosity and vice versa. The thermal evolution of ligand binding kinetics suggests, with other results, an interplay between high-fruqurncy transitions of the amino acid side chains and low-frequency collective motions as a possible regulatory mechanism of protein dynamics.

Structure-dynamics-function relationships in Asian elephant (Elephas maximus) myoglobin. An optical spectroscopy and flash photolysis study on functionally important motions

“…Only process III is populated in the whole 40-300 K temperature range, and therefore it can be identified as the "classical pocket process" already described in the literature for ligand binding to a number of heme proteins (Austin et al, 1975;Di Iorio et al, 1991;Di Iorio, 1992;Doster et al, 1982 andStetzkowski et al, 1985). Below 180 K the peak activation enthalpy of process III is about 18 kJ/mol, considerably higher than the -10 kJ/mol reported in the literature for the low-temperature pocket process in Sw-Mb or the --13 kJ/mol found for Ho-Mb (Table 3).…”

“…The enthalpy distribution becomes progressively narrower as temperature rises, leading to an exponential binding above -240 K. On the other hand, the peak enthalpy increases from -28 kJ/mol at -180 K to nearly 33 kJ/mol at -220 K and then starts decreasing to reach again -28 kJ/mol at -260 K. Furthermore, the fractional amplitude of process IV is strongly influenced by temperature: it starts from zero below 110 K and increases to more than 0.5 at -230 K to drop again to zero at -290K. On the basis of these features we propose that process IV is related to a dynamic channel within the protein matrix through which the ligand can migrate, a ri-edition of the matrix process in the multibarrier model (Ansari et al, 1986;Austin et al, 1975;Di Iorio, 1992). The probability of the photolyzed CO molecule entering the channel is proportional to the frequency with which the "dynamic gate" opens and therefore rises with temperature.…”

Stereodynamic properties of the cooperative homodimeric Scapharca inaequivalvis hemoglobin studied through optical absorption spectroscopy and ligand rebinding kinetics

“…Thereby, information on the stereodynamic properties of the active site and, in particular, on the presence of nonharmonic contributions to nuclear motions that play a relevant role in protein function can be obtained (Di Pace et al, 1992;Cupane et al, 1993a). On the other hand, analysis of the ligand rebinding kinetics after flash photolysis of the CO derivative enables one to establish a connection between protein matrix fluctuations and functional behavior (Steinbach et al, 1991;Di Iorio, 1992).…”

Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins

“…Although the structure of the Hb unit has been determined to atomic resolution (Fermi et al, 1987), less is known about the effects of the protein-heme interaction on the spectroscopic properties of the heme (Boxer et al, 1982;Clarke et al, 1982). Also, an accurate description of the dynamics of the protein environment of the heme (Bismuto et al, 1989a,b;Diiorio, 1992;Dipace et al, 1992) is still lacking. Holeburning experiments on crystallized chlorophyllide-substituted myoglobins have shown that the protein environment in the heme pocket is not as uniform as in a crystal (Bismuto et al, 1989a,b), but resembles that of a disordered glass, due to the dynamic equilibrium between a large number of protein conformations.…”