DO GLOBULAR-PROTEINS REQUIRE SOME STRUCTURAL PECULIARITY TO BEST FUNCTION AT HIGH-TEMPERATURES

Our knowledge of protein thermodynamics is limited to proteins from mesophilic sources. We propose a model showing how proteins from thermophilic organisms may be best adapted to function at temperatures that usually determine the unfolding of mesophilic proteins. We find that the ratio between unfolding enthalpy and entropy evaluated at the respective convergence temperatures is almost constant among mesophilic globular proteins. While this result is an expected one for proteins that were shown to obey unfolding enthalpy-entropy convergence, it is less plain for those proteins whose residual enthalpy and entropy at the respective convergence temperatures are quite far from the convergence values. This ratio can be considered a melting temperature that reflects the crystallike protein packing. It seems to be a universal property of globular proteins, irrespective of their different origins. On this basis we suggest that the residual unfolding enthalpy and entropy, which were shown to be associated with hydrogen bond and van der Waals interactions, might play a major role in the thermal stabilization of proteins from organisms Living under extreme conditions.