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Electrochemistry is the science involved in the interconversion of electrical and chemical reactions. Such reactions are called reduction-oxidation, or redox reactions. These important reactions are defined by changes in oxidation states for one or more reactant elements and include a subset of reactions involving the transfer of electrons between reactant species. Electrochemistry as a field has evolved to yield sufficient insights on the fundamental principles of redox chemistry and multiple...
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Redox-coupled quinone dynamics in the respiratory complex I.

Judith Warnau1,2, Vivek Sharma3,4, Ana P Gamiz-Hernandez1

  • 1Department Chemie, Technische Universität München, D-85748 Garching, Germany.

Proceedings of the National Academy of Sciences of the United States of America
|August 19, 2018
PubMed
Summary
This summary is machine-generated.

Complex I uses quinone (Q) reduction to pump protons. Simulations reveal Q dynamics are redox-state dependent, with distinct binding sites in the Q tunnel, suggesting a mechanism for long-range proton-electron coupling.

Keywords:
NADH:ubiquinone oxidoreductasecell respirationdiffusion modelelectron transfermolecular simulations

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Bioenergetics

Background:

  • Complex I is crucial for cellular respiration, coupling quinone (Q) reduction to proton pumping across membranes.
  • A significant distance separates the Q reduction site from the proton-pumping domain, posing a challenge to understanding proton-electron coupling.

Purpose of the Study:

  • To elucidate the molecular mechanism of long-range proton-electron coupling in Complex I.
  • To investigate the redox-state-dependent dynamics and binding sites of quinone (Q) within Complex I.

Main Methods:

  • Full atomistic molecular dynamics simulations.
  • Free energy calculations.
  • Continuum electrostatics calculations on Complex I from *Thermus thermophilus*.

Main Results:

  • Quinone (Q) dynamics are redox-state dependent, with quinol (QH2) moving to a Q-binding site within the Q tunnel.
  • A second Q-binding site was identified near the membrane domain opening, with specific interactions between the Q headgroup and protein residues.
  • The effective diffusion coefficient of Q in the tunnel was estimated, providing characteristic times for Q and QH2 movement.

Conclusions:

  • Quinone (Q) movement within the Q tunnel is redox-state dependent and involves distinct binding sites formed by conserved residues.
  • This redox-state-dependent Q motion is proposed to be coupled to the proton-pumping machinery of Complex I, explaining long-range proton-electron coupling.