title: In Polytomella sp. mitochondria, biogenesis of the heterodimeric COX2 subunit of cytochrome c oxidase requires two different import pathways.
abstract: In the vast majority of eukaryotic organisms, the mitochondrial cox2 gene encodes subunit II of cytochrome c oxidase (COX2). However, in some lineages including legumes and chlorophycean algae, the cox2 gene migrated to the nucleus. Furthermore, in chlorophycean algae, this gene was split in two different units. Thereby the COX2 subunit is encoded by two independent nuclear genes, cox2a and cox2b, and mitochondria have to import the cytosol-synthesized COX2A and COX2B subunits and assemble them into the cytochrome c oxidase complex. In the chlorophycean algae Chlamydomonas reinhardtii and Polytomella sp., the COX2A precursor exhibits a long (130-140 residues), cleavable mitochondrial targeting sequence (MTS). In contrast, COX2B lacks an MTS, suggesting that mitochondria use different mechanisms to import each subunit. Here, we explored the in vitro import processes of both, the Polytomella sp. COX2A precursor and the COX2B protein. We used isolated, import-competent mitochondria from this colorless alga. Our results suggest that COX2B is imported directly into the intermembrane space, while COX2A seems to follow an energy-dependent import pathway, through which it finally integrates into the inner mitochondrial membrane. In addition, the MTS of the COX2A precursor is eliminated. This is the first time that the in vitro import of split COX2 subunits into mitochondria has been achieved.
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autonoma de México, Apartado Postal 70-23, México 04510, D.F., Mexico.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Jiménez-Suárez
authors.forename: Miriam
authors.initials: M
authors.lastname: Vázquez-Acevedo
authors.forename: Andrés
authors.initials: A
authors.lastname: Rojas-Hernández
authors.forename: Soledad
authors.initials: S
authors.lastname: Funes
authors.forename: Salvador
authors.initials: S
authors.lastname: Uribe-Carvajal
authors.forename: Diego
authors.initials: D
authors.lastname: González-Halphen
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology; D000460:Chlorophyta / Q000201:enzymology*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D008954:Models, Biological; D010455:Peptides / Q000378:metabolism; D055503:Protein Multimerization; D011498:Protein Precursors / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats
chemical_list: D010455:Peptides; D011498:Protein Precursors; D021122:Protein Subunits; D000444:Aldehyde Dehydrogenase; D003576:Electron Transport Complex IV