The structure of Na+-translocating of NADH:ubiquinone oxidoreductase of Vibrio cholerae: implications on coupling between electron transfer and Na+ transport

Abstract

The Na⁺-translocating NADH:ubiquinone oxidoreductase (Na⁺-NQR) of Vibrio cholerae is a respiratory complex that couples the exergonic oxidation of NADH to the transport of Na⁺ across the cytoplasmic membrane. It is composed of six different subunits, NqrA, NqrB, NqrC, NqrD, NqrE, and NqrF, which harbor FAD, FMN, riboflavin, quinone, and two FeS centers as redox co-factors. We recently determined the X-ray structure of the entire Na⁺-NQR complex at 3.5-Å resolution and complemented the analysis by high-resolution structures of NqrA, NqrC, and NqrF. The position of flavin and FeS co-factors both at the cytoplasmic and the periplasmic side revealed an electron transfer pathway from cytoplasmic subunit NqrF across the membrane to the periplasmic NqrC, and via NqrB back to the quinone reduction site on cytoplasmic NqrA. A so far unknown Fe site located in the midst of membrane-embedded subunits NqrD and NqrE shuttles the electrons over the membrane. Some distances observed between redox centers appear to be too large for effective electron transfer and require conformational changes that are most likely involved in Na⁺ transport. Based on the structure, we propose a mechanism where redox induced conformational changes critically couple electron transfer to Na⁺ translocation from the cytoplasm to the periplasm through a channel in subunit NqrB.

The aerobic respiratory chain of Pseudomonas aeruginosa cultured in artificial urine media: Role of NQR and terminal oxidases

“…Moreover, in a previous report we proposed that NQR could be important for pathogenic bacteria when iron is limiting [91], which is relevant for the infection since the immune system produces iron chelators that deprive pathogens of this essential nutrient. NQR is the ion-pumping NADH dehydrogenase that requires the least amount of iron for its assembly (1 or 2 atoms per molecule [20,21,92,93]), which could allow an active bioenergetic metabolism and cell survival during infection, in particular when the immune response has been mounted.…”

NaCl promotes antibiotic resistance by reducing redox states in Vibrio alginolyticus

“…This enzyme is composed of six different subunits, NqrA, NqrB, NqrC, NqrD, NqrE and NqrF. An electron transfer pathway links the cytoplasmic subunit NqrF across the membrane to the periplasmic NqrC, and via NqrB back to the quinone reduction site on cytoplasmic NqrA (Steuber et al, 2015). Thus, Western blotting was used to detect the abundance of NqrA, NqrC and NqrF.…”

Metabolic Reprogramming of Vibrio cholerae Impaired in Respiratory NADH Oxidation Is Accompanied by Increased Copper Sensitivity

“…The NQR is a membrane-bound flavo-iron sulfur protein complex composed of six subunits (9). The enzyme is of central importance for V. cholerae, since the electrochemical Na ϩ gradient generated by the NQR drives many other cellular processes, such as flagellar rotation, exchange of cations, and expulsion of antibiotics (10)(11)(12).…”