Protein unfolding by mitochondria - The Hsp70 import motor

Protein unfolding is a key step in the import of some proteins into mitocho ndria and chloroplasts and in the degradation of regulatory proteins by ATP -dependent proteases. In contrast to protein folding, the reverse process h as remained largely uninvestigated until now. This review discusses recent discoveries on the mechanism of protein unfolding during translocation into mitochondria. The mitochondria can actively unfold preproteins by unraveli ng them from the N-terminus. The central component of the mitochondrial imp ort motor, the matrix heat shock protein 70, functions by bath pulling and holding the preproteins.