Protein stabilization by naturally occurring osmolytes.

Natural selection is believed to be an unforgiving and relentless force in the evolution of life on earth. An organism that cannot adapt to a changing environment or an environment hostile to cell functions is at risk as a species. So it is important to understand the mechanisms used by plants, animals, and microorganisms in adapting to environments in the biosphere that would ordinarily denature proteins or otherwise cause disruption of life-giving cellular processes. These hostile environments involve such stresses as extremes of temperature, cellular dehydration, desiccation, high extracellular salt environments, and even the presence of denaturing concentrations of urea inside cells (1). It has been recognized for some time that many plants, animals, and microorganisms that have adapted to environmental extremes also accumulate significant intracellular concentrations of small organic molecules (1–4). From these (and other) observations comes the hypothesis that these small organic molecules, called osmolytes, have the ability to protect the cellular components against denaturing environmental stresses (1–5). In this chapter, we seek to understand the molecular-