Insertion of MOM22 into the mitochondrial outer membrane strictly depends on surface receptors

Targeting of preproteins to mitochondria and their translocation across the outer membrane are mediated by the mitochondrial receptor complex. This protein complex contains the import receptors MOM19 and MOM72 and the general insertion pore GIP. All seven components of the receptor complex are synthesized in the cytosol and thus have to be targeted to the mitochondria themselves. Here we investigated the import pathway of the precursor of MOM22 into the outer membrane. In contrast to other mitochondrial preproteins studied so far, the import of MOM22 absolutely depended on the presence of surface receptors. In fact, both receptors MOM19 and MOM72 were involved in its import pathway. The targeting of MOM22 to mitochondria is thus highly specific and controlled.