Abstract
In fungi, the mitochondrial respiratory chain complexes (complexes I-IV) are responsible for oxidative phosphorylation, as in higher eukaryotes. Cryo-EM was used to identify a 200 kDa membrane protein from Neurospora crassa in lipid nanodiscs as cytochrome c oxidase (complex IV) and its structure was determined at 5.5 Å resolution. The map closely resembles the cryo-EM structure of complex IV from Saccharomyces cerevisiae. Its ten subunits are conserved in S. cerevisiae and Bos taurus, but other transmembrane subunits are missing. The different structure of the Cox5a subunit is typical for fungal complex IV and may affect the interaction with complex III in a respiratory supercomplex. Additional density was found between the matrix domains of the Cox4 and Cox5a subunits that appears to be specific to N. crassa.
Highlights
IntroductionThe mitochondrial respiratory chain consists of NADH dehydrogenase (complex I), succinate dehydrogenase (complex II), cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV)
The mitochondrial respiratory chain consists of NADH dehydrogenase, succinate dehydrogenase, cytochrome c reductase and cytochrome c oxidase
We report the 5.5 Aresolution structure of complex IV from N. crassa reconstituted into lipid nanodiscs, as determined by single-particle cryo-EM
Summary
The mitochondrial respiratory chain consists of NADH dehydrogenase (complex I), succinate dehydrogenase (complex II), cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV). Mitochondrial complex IV is a 200 kDa heme-copper oxidase with up to 14 different polypeptides (Balsa et al, 2012). Complex IV catalyzes the reduction of molecular oxygen to water and conserves free energy by pumping protons across the mitochondrial inner membrane (Wikstrom, 1977). Owing to the high-resolution crystal structure of bovine heart complex IV (Tsukihara et al, 1995, 1996), the molecular mechanisms of the three central subunits as a redox-coupled proton pump are well understood (Yoshikawa et al, 2011; Shinzawa-Itoh et al, 2007; Liang et al, 2017). There is genetic evidence in yeast (Capaldi, 1990) that most of the peripheral subunits function as assembly factors of complex IV. Null mutants yield enzymes with reduced activities compared with the wild type
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