The chaperone function: meanings and myths

What are molecular chaperones and how should we think about them? We propose that it is better to think in terms of a chaperone function rather than in terms of chaperone molecules. We define the chaperone function as the prevention or reversal of incorrect interactions that may occur when reactive macromolecular surfaces are transiently exposed to the intracellular environment. We suggest that this function is a distinct and essential cellular function, mediated by many different proteins. Chaperones have evolved to reduce, by a variety of mechanisms, the aggregation of proteins into non-functional, and sometimes cytotoxic, structures. Chaperones may also have evolved to have additional roles. A cellular or extracellular event mediated by a chaperone protein is not necessarily a consequence of that protein's chaperone function. The aim of this article is to provide a brief summary of the origin and concepts used in the intracellular chaperone field, to provide a backdrop for discussion of their possible roles outside the cell.