THE STRUCTURAL BASIS OF PROTEIN HALOPHILICITY

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