The ATP-driven protein translocation-motor of mitochondria

The majority of mitochondrial proteins are encoded in the nucleus. In the cytosol they are synthesized as precursor proteins which are transported into mitochondria. Protein import into mitochondria requires a concerted action of a variety of different proteins. For the transport of precursor proteins across the mitochondrial inner membrane and their folding in the matrix the mitochondrial hsp70 (mhsp70) chaperone plays an essential role. Mhsp70 is found in at least two protein complexes within mitochondria: together with Tim44 and mGrpE, mhsp70 forms the import-complex and together with Mdj1 and mGrpE i t forms a folding-complex. This review focuses on the function of the import-complex. It is believed that mhsp70 can act as a mechanochemical enzyme that actively pulls precursor proteins across the inner membrane.