Evolution of respiratory complex I: "supernumerary" subunits are present in the alpha-proteobacterial enzyme.
Modern α-proteobacteria are thought to be closely related to the ancient symbiont of eukaryotes, an ancestor of mitochondria. Respiratory complex I from α-proteobacteria and mitochondria is well conserved at the level of the 14 "core" subunits, consistent with that notion. Mitochondrial complex I contains the core subunits, present in all species, and up to 31 "supernumerary" subunits, generally thought to have originated only within eukaryotic lineages. However, the full protein composition of an α-proteobacterial complex I has not been established previously. Here, we report the first purification and characterization of complex I from the α-proteobacterium Paracoccus denitrificans. Single particle electron microscopy shows that the complex has a well defined L-shape. Unexpectedly, in addition to the 14 core subunits, the enzyme also contains homologues of three supernumerary mitochondrial subunits as follows: B17.2, AQDQ/18, and 13 kDa (bovine nomenclature). This finding suggests that evolution of complex I via addition of supernumerary or "accessory" subunits started before the original endosymbiotic event that led to the creation of the eukaryotic cell. It also provides further confirmation that α-proteobacteria are the closest extant relatives of mitochondria.
Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, United Kingdom.
Chui-ying
CY
Yip
Michael E
ME
Harbour
Kamburapola
K
Jayawardena
Ian M
IM
Fearnley
Leonid A
LA
Sazanov
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D020134:Catalytic Domain / Q000235:genetics; D002417:Cattle; D042967:Electron Transport Complex I / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D010231:Paracoccus denitrificans / Q000201:enzymology / Q000235:genetics*
D001426:Bacterial Proteins; D024101:Mitochondrial Proteins; D042967:Electron Transport Complex I