Of sequence and structure: Strategies of protein thermostability in evolutionary perspective

In this work we employ various methods of analysis (unfolding simulations and comparative analysis of structures and sequences of proteomes of thermophilic organisms) to show that organisms can follow two major strategies of thermophilic adaptation: (i) General, non-specific, structure-based, when proteomes of certain thermophilic organisms show significant structural bias toward proteins of higher compactness. In this case thermostability is achieved by greater overall number of stabilizing contacts, none of which may be especially strong, and (ii) Specific, sequence-based, whereby sequence variations aimed at strengthening specific types of interactions (e.g. electrostatics) are applied without significantly changing structures of proteins. The choice of a certain strategy is a direct consequence of evolutionary history and environmental conditions of particular (hyper) thermophilic species: ancient hyperthermophilic organisms that directly evolved in hot environment, pursued mostly structure-based strategy, while later evolved organisms whose thermophilic adaptation was a consequence of their recolonization of hot environment, pursued specific, sequence-based strategy of thermophilic adaptation.