Molecular Basis of the Biological Compatibility of Nature’s Osmolytes

Abstract

With the exception of halophilic bacteria, essentially all cells respond to a hyperosmotic stress with an accumulation of certain relatively nontoxic, organic solutes (Yancey et al. 1982; Jones et al. 1977; Costa and Pierce 1983). These compatible solutes or osmolytes have been shown by the speakers at this symposium and others to have unique properties which render them especially fit to serve as intracellular solutes. The purpose of this chapter is to review the fundamental reasons why some solutes (including those commonly used by nature) are “kind” to protein structures and functions and why others are not. While the original literature dealing with this topic relies heavily on thermodynamic arguments to describe protein-solute interactions, this review will attempt to treat the subject matter largely descriptively. In some cases, this requires an interpretation or simplification of thermodynamic observations which may not be totally accurate. However, it is hoped that the benefit of having a physical explanation of solute effects on protein structure will partially offset the disadvantage of not having a rigorous analysis of the various concepts.