Sodium-dependent movement of covalently bound FMN residue(s) in Na(+)-translocating NADH:quinone oxidoreductase.
Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) is a component of respiratory electron-transport chain of various bacteria generating redox-driven transmembrane electrochemical Na(+) potential. We found that the change in Na(+) concentration in the reaction medium has no effect on the thermodynamic properties of prosthetic groups of Na(+)-NQR from Vibrio harveyi, as was revealed by the anaerobic equilibrium redox titration of the enzyme's EPR spectra. On the other hand, the change in Na(+) concentration strongly alters the EPR spectral properties of the radical pair formed by the two anionic semiquinones of FMN residues bound to the NqrB and NqrC subunits (FMN(NqrB) and FMN(NqrC)). Using data obtained by pulse X- and Q-band EPR as well as by pulse ENDOR and ELDOR spectroscopy, the interspin distance between FMN(NqrB) and FMN(NqrC) was found to be 15.3 Å in the absence and 20.4 Å in the presence of Na(+), respectively. Thus, the distance between the covalently bound FMN residues can vary by about 5 Å upon changes in Na(+) concentration. Using these results, we propose a scheme of the sodium potential generation by Na(+)-NQR based on the redox- and sodium-dependent conformational changes in the enzyme.
Department of Molecular Energetics of Microorganisms, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
Michael I
MI
Verkhovsky
Alexander V
AV
Bogachev
Andrey V
AV
Pivtsov
Yulia V
YV
Bertsova
Matvey V
MV
Fedin
Dmitry A
DA
Bloch
Leonid V
LV
Kulik
D001692:Biological Transport; D004578:Electron Spin Resonance Spectroscopy; D005486:Flavin Mononucleotide / Q000737:chemistry* / Q000378:metabolism*; D009068:Movement; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011808:Quinone Reductases / Q000737:chemistry* / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013816:Thermodynamics; D014733:Vibrio / Q000201:enzymology
D005486:Flavin Mononucleotide; D012964:Sodium; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases