New Class of Bacterial Membrane Oxidoreductases

A new class of bacterial multisubunit membrane-bound electron-transfer complexes has been identified based on biochemical and bioinformatic data. It contains subunits homologous to the three-subunit molybdopterin oxidoreductases and four additional subunits, two of which are c-type cytochromes. The complex was purified from the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus, and putative operons for similar complexes were identified in a wide range of bacteria. In most cases, the presence of the new complex is anticorrelated with the cytochrome bc or bf electron-transfer complex, suggesting that it replaces it functionally. This appears to be a widespread yet previously unrecognized protein complex involved in energy metabolism in bacteria.