THE TEMPERATURE DEPENDENCE OF DYNAMICS OF HYDRATED MYOGLOBIN

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Eleven molecular dynamics simulations of 150 psec in length are carried out on the carboxy-myoglobin protein at 20, 60, 100, 180, 220, 240, 260, 280, 300, 320 and 340 K. The simulations attempt to mimic neutron scattering experiments very closely by including 349 waters around the protein. Theoretically determined elastic, quasielastic, and inelastic neutron scattering data are directly compated with experiment. The elastic scattering is decreased compared to experiment. Inelastic and quasielastic spectra show that the inelastic peak is shifted to lower frequency than the experimental value, while quasielastic behavior is in good agreement with experiment. In addition, we analyze simulation trajectories by comparing rms deviations from the starting structure, average atomic fluctuations, and a helical time series. The anisotropy and anharmonicity of the atomic position distributions are also determined, The anisotropy is small below 180 K and dramatically increases above this temperature. The anharmonicity is large at all temperatures. Overall simulation results indicate that the protein behaves with near harmonic vibration in well defined substates at temperatures below 180 K. Protein behavior becomes much more anharmonic with transitions between many conformational substates at higher temperatures.