Chaperone Function: The Orthodox View

Introduction The term molecular chaperone came into general use after the appearance of an article in Nature that suggested it was an appropriate phrase to describe a newly defined intracellular function – the ability of several unrelated protein families to assist the correct folding and assembly/disassembly of other proteins [1]. The identification of the chaperonin family of molecular chaperones in the following year [2] triggered a tidal wave of research in several laboratories aimed at unravelling how the GroEL/GroES chaperones, and later the DnaK/DnaJ chaperones, from Escherichia coli facilitate the folding of newly synthesised polypeptide chains and the refolding of denatured proteins. This wave continues to surge, with the result that much detailed information is available about the structure and function of those families of chaperone that assist protein folding [3]. It is now well established that a subset of proteins requires this chaperone function, not because chaperones provide steric information required for correct folding but because chaperones inhibit side reactions that would otherwise cause some of the chains to form non-functional aggregates. The number of different protein families described as chaperones is now more than 25 – some, but not all, of which are also stress proteins – and there is no slackening in the rate of discovery of new ones. The success of this wave of research has changed the paradigm of protein folding from the earlier view that it is a spontaneous self-assembly process to the current view that it is an assisted self-assembly process [4].