The structural basis of protein halophilicity

The halophilic Archaea live in hypersaline environments and maintain an osmotic balance by accumulating intracellular concentrations of salt (mainly KCI) that are isotonic with the exterior. Therefore, their cellular components are adapted to concentrations of KCl approaching 5 M and often require these levels of salt for stability and function. Here, we consider the effects of hypersalinity on protein structure and then review the known structures of proteins from the halophilic Archaea in the context of these effects. Specific proteins considered are ferredoxin, malate dehydrogenase, dihydrofolate reductase, dihydrolipoamide dehydrogenase nase and elongation factor Tu. From the available data, models for the structural basis of halophilicity are discussed and analysed. (C) 1997 Elsevier Science Inc.