| Abstract: | The plant mitochondrial cytochrome bc1 complex, like nonplant mitochondrial complexes,consists of cytochromes b and c1, the Rieske iron–sulfur protein, two Core proteins, and fivelow-molecular mass subunits. However, in contrast to nonplant sources, the two Core proteinsare identical to subunits of the general mitochondrial processing peptidase (MPP). The MPPis a fascinating enzyme that catalyzes the specific cleavage of the diverse presequence peptidesfrom hundreds of the nuclear-encoded mitochondrial precursor proteins that are synthesizedin the cytosol and imported into the mitochondrion. Integration of the MPP into the bc1complex renders the bc1 complex in plants bifunctional, being involved both in electrontransport and in protein processing. Despite the integration of MPP into the bc1 complex,electron transfer as well as translocation of the precursor through the import channel areindependent of the protein-processing activity. Recognition of the processing site by MPPoccurs via the recognition of higher-order structural elements in combination with charge andcleavage-site properties. Elucidation of the three-dimensional (3-D) structure of the mammaliancytochrome bc1 complex is highly useful for understanding of the mechanism of action of MPP.In memory of my teacher—an insightful, devoted, and enthusiastic scientist and an amiable and kind-hearted human being—Lars Ernster |
