Receptor-mediated recruitment of cytosolic J-proteins to the mitochondrial outer membrane promotes assembly of preprotein translocases

Mitochondria possess elaborate machineries for the import of preproteins from the cytosol. Cytosolic factors like Hsp70 chaperones and their co-chaperones, the J-proteins, guide preproteins to the mitochondrial surface. The translocase of the mitochondrial outer membrane (TOM) forms the entry gate for precursor proteins. How proteins are delivered to the receptors Tom20, Tom22 and Tom70 is only understood in part. We identified the cytosolic J-protein Xdj1 as a specific interaction partner of the central receptor Tom22. Tom22 recruits Xdj1 to the mitochondrial surface to promote assembly of the TOM complex. A second J-protein of the cytosol, Djp1, binds to Tom70 to mediate biogenesis of the mitochondrial import (MIM) complex. Thus, by targeting distinct TOM receptors, cytosolic J-proteins promote the biogenesis of different mitochondrial preprotein translocases.