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

Our knowledge of protein thermodynamics is limited to proteins from me sophilic sources. We propose a model showing how proteins from thermop hilic organisms may be best adapted to function at temperatures that u sually determine the unfolding of mesophilic proteins. We find that th e ratio between unfolding enthalpy and entropy evaluated at the respec tive convergence temperatures is almost constant among mesophilic glob ular 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 re spective convergence temperatures are quite far from the convergence v alues. This ratio can be considered a melting temperature that reflect s the crystallike protein packing. It seems to be a universal property of globular proteins, irrespective of their different origins. On thi s basis we suggest that the residual unfolding enthalpy and entropy, w hich 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.