Eurytolerant Proteins: Mechanisms for Extending the Environmental Tolerance Range of Enzyme-Ligand Interactions

Abstract

Sufficient mechanisms seem available to proteins to enable adjustment of ligand-binding enthalpies and volumes to whatever values are optimal on biological gorunds. Thus, enzymes and respiratory proteins can develop the capacities to function satisfactorily over wide ranges of temperature and hydrostatic pressure. The adjustments ("titrations") of ligand-binding enthalpies and volumes may involve large portions of a protein molecule. Amino acid substitutions throughout the protein, even at regions remote from so-called active sites, may be critically important in environmental adaptation processes. Thus, a far larger proportion of amino acid residues may be sensitive to strong selective pressures than has been proposed by the "neutralist" school of protein evolution.