In this review, I briefly describe the distinct evolutionary history of each of the major heat-shock protein families (HSPs). If you view the cell as a complex and optimized machine and study only the heat-shock response and chaperone network in a single species, such as humans, yeast or Arabidopsis, you would find a complex molecular machinery with many ‘parts’ or proteins that work in a co-ordinate fashion to disaggregate and fold proteins. The close association and importance of these proteins parts would lead you to believe that this cellular machine could not work if some parts were missing, had been differentially manufactured or were present in differing amounts. Yet, this is just what we find when we look at the evolution of the HSPs. What makes the evolution of the HSPs and the chaperone network so fascinating is that, on the one hand, the HSPs are highly conserved, work in a collaborative fashion and are necessary for life. On the other hand, each domain of life (Archaea, Bacteria and Eukarya) has a different subset of HSPs, and each HSP family has a unique evolutionary history.

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