Localization of ubiquinone-8 in the Na +-pumping NADH: Quinone oxidoreductase from Vibrio cholerae

Abstract

Na + is the second major coupling ion at membranes after protons, and many pathogenic bacteria use the sodium-motive force to their advantage. A prominent example is Vibrio cholerae, which relies on the Na +-pumping NADH:quinone oxidoreductase (Na +-NQR) as the first complex in its respiratory chain. The Na +-NQR is a multisubunit, membrane-embedded NADH dehydrogenase that oxidizes NADH and reduces quinone to quinol. Existing models describing redox-driven Na + translocation by the Na +-NQRare based on the assumption that the pump contains four flavins and one FeS cluster. Here we show that the large, peripheral NqrA subunit of the Na +-NQR binds one molecule of ubiquinone-8. Investigations of the dynamic interaction of NqrA with quinones by surface plasmon resonance and saturation transfer difference NMR reveal a high affinity, which is determined by the methoxy groups at the C-2 and C-3 positions of the quinone headgroup. Using photoactivatable quinone derivatives, it is demonstrated that ubiquinone- 8 bound to NqrA occupies a functional site. A novel scheme of electron transfer in Na +-NQR is proposed that is initiated by NADH oxidation on subunit NqrF and leads to quinol formation on subunit NqrA. © 2011 by The American Society for Biochemistry and Molecular Biology Inc.