Dynamic Fingerprints of Protein Thermostability Revealed by Long Molecular Dynamics

The dynamical requirements for protein thermostability are a subject of intense debate since different techniques are sensitive to different dynamical processes. The present investigation arises from a neutron scattering experiment pointing to the lower temperature dependence of the flexibility of thermophilic proteins as a mechanism of enhanced thermostability. By means of 200 ns molecular dynamics simulations at different temperatures, we have investigated the differences in internal dynamics of the thermo-mesophilic pair of proteins studied in the experiment. The present work exceeds the time scales explored by the experiment and former studies on other thermo-mesophilic pairs by several orders of magnitude. Our simulations confirm the different thermal behavior observed in the experiment and suggest that both reduced coil segments and salt bridge interactions contribute to lowering the increase in flexibility with temperature. Moreover, the mesophilic protein exhibits a more heterogeneous distribution of residue mobilities involving more local motions. We suggest that the more collective motions of the thermophilic protein underlie a broader energy landscape.