Organismal, Ecological, and Evolutionary Aspects of Heat-Shock Proteins and the Stress Response: Established Conclusions and Unresolved Issues

Abstract

How heat-shock proteins function in diverse organisms from diverse environments, and how this diversification has evolved, is an emerging focus of research on molecular chaperones. As molecular chaperones, heat-shock proteins play diverse cellular roles, typically in minimizing dysfunction that may occur when other proteins are in non-native conformations. The standard aspects of these roles in vitro , in isolated cells, and in typical model organisms in the laboratory are now well-established, as are the ubiquity of heat-shock proteins in organisms, the range of stresses that induce heat-shock proteins, the major families of heatshock proteins, their expression in nature, and their variation along natural gradients of stress. These aspects may no longer require extensive examination. By contrast, the frequency of natural expression of heat-shock proteins, their exact physiological roles in stress tolerance at levels of biological organization above the cell, the exact molecular mechanisms by which heat-shock protein expression and function has become tuned to the prevailing level of environmental stress, and the fitness consequences of heat-shock protein expression in nature are among the numerous unresolved issues in this area.