THE MITOCHONDRIAL RECEPTOR COMPLEX - A CENTRAL ROLE OF MOM22 IN MEDIATING PREPROTEIN TRANSFER FROM RECEPTORS TO THE GENERAL INSERTION PORE

The receptor complex in the mitochondrial outer membrane, which consis ts of at least seven different proteins, is responsible for the recogn ition and translocation of cytosolically synthesized preproteins. Two of its subunits, MOM19 and MOM72, function as surface receptors for pr eproteins. Four other subunits (MOM38, MOM30, MOM8, and MOM7) have bee n suggested to constitute the general insertion pore (GIP). Here we re port on the structure and function of MOM22. MOM22 is anchored in the outer membrane by a single transmembrane segment. The highly negativel y charged N-terminal domain is exposed to the cytosol and the C-termin al domain to the intermembrane space. MOM22 appears to be a central co mponent of the receptor complex, required for the transfer of preprote ins from the receptors to the GIP. We speculate that the negatively ch arged domain of MOM22 is involved in the transfer of positively charge d signal sequences of preproteins.