A Quinol Anion as Catalytic Intermediate Coupling Proton Translocation With Electron Transfer in E. coli Respiratory Complex I

Abstract

Energy-converting NADH:ubiquinone oxidoreductase, respiratory complex I, plays a major role in cellular energy metabolism. It couples NADH oxidation and quinone reduction with the translocation of protons across the membrane, thus contributing to the protonmotive force. Complex I has an overall L-shaped structure with a peripheral arm catalyzing electron transfer and a membrane arm engaged in proton translocation. Although both reactions are arranged spatially separated, they are tightly coupled by a mechanism that is not fully understood. Using redox-difference UV-vis spectroscopy, an unknown redox component was identified in Escherichia coli complex I as reported earlier. A comparison of its spectrum with those obtained for different quinone species indicates features of a quinol anion. The re-oxidation kinetics of the quinol anion intermediate is significantly slower in the D213GH variant that was previously shown to operate with disturbed quinone chemistry. Addition of the quinone-site inhibitor piericidin A led to strongly decreased absorption peaks in the difference spectrum. A hypothesis for a mechanism of proton-coupled electron transfer with the quinol anion as catalytically important intermediate in complex I is discussed.

Resolving Chemical Dynamics in Biological Energy Conversion: Long-Range Proton-Coupled Electron Transfer in Respiratory Complex I

“…The p K a ’s of the buried carboxylates at this region are highly shifted from their solution values based on QM/MM as well as electrostatic calculations, although the computational treatment of the exact titration behavior is highly challenging. Interestingly, recent spectroscopic data provide possible further support for the involvement of QH – species . The Q reduction and diffusion to the second binding site have also been found to link to conformational changes in several dynamically flexible loop regions surrounding the subunit (Figure a) that are partially explored during microsecond aMD simulations as well as millisecond cgMD simulations. , …”

“…Interestingly, recent spectroscopic data provide possible further support for the involvement of QH − species. 58 The Q reduction and diffusion to the second binding site have also been found to link to conformational changes in several dynamically flexible loop regions surrounding the subunit (Figure 3a) that are partially explored during microsecond aMD simulations as well as millisecond cgMD simulations. 2,32 It is also worth noting that while the discussed computational methods have their unique power in probing complex biochemical processes, they also have their limitations.…”

The clinically relevant triple mutation in the mtND1 gene inactivates Escherichia coli complex I

“…According to this hypothesis, the quinol anion moves further in its binding cavity to reach a site where it is fully protonated. The proton required for the re-protonation of the quinol anion might be derived from the membrane arm of the complex after proton translocation is completed [2,25,34,35].…”

“…It turned out that the single variant is stably assembled and showed a decreased electron transfer activity that was fully coupled to proton translocation. Remarkably, this variant exhibits significant activation kinetics, which was interpreted as a disturbed Q chemistry [2,25,[34][35][36]. Various amino acid residues are found in positions L200 (e.g.…”

Docking and molecular simulations reveal a quinone‐binding site on the surface of respiratory complex I

“…Rich [67] pointed out that the quinol anion (QH -) can act as a much better reductant than the neutral QH 2 species for a potential quinol to quinone electron transfer. QH À species have indeed been suggested to be central to the complex I mechanism [17,[68][69][70]. Such a species may stabilize at site 5 of the Q-binding tunnel triggered by proton release towards acidic groups (Asp53) in the vicinity.…”