[Mitochondrial Hsp70 - function and evolution]

Hsp70 molecular chaperones function in variety of critical cellular processes, including protein folding, translocation of proteins across membranes and assembly/disassembly of protein complexes. Hsp70 systems consist of a core Hsp70 protein and its co-chaperones: J-protein and nucleotide release factor NRF. These co-chaperones regulate the cycle of interaction with protein substrate via stimulating the ATPase activity of Hsp70 (J-protein) and promoting nucleotide exchange (NRF). Compartments within the eukaryotic cell often contain multiple Hsp70s, J-proteins and NRFs. The capabilities of these systems to carry out diverse cellular functions results from either specialization of an Hsp70 or by interaction of multifunctional Hsp70 with an array of specialized J-proteins. The well-studied Hsp70 systems of yeast mitochondria provide an excellent example of functional divergence and evolution of Hsp70 machineries.