Dual mechanism of ion permeation through VDAC revealed with inorganic phosphate ions and phosphate metabolites

PLoS One. 2015 Apr 10;10(4):e0121746. doi: 10.1371/journal.pone.0121746. eCollection 2015.

Abstract

In the exchange of metabolites and ions between the mitochondrion and the cytosol, the voltage-dependent anion channel (VDAC) is a key element, as it forms the major transport pathway for these compounds through the mitochondrial outer membrane. Numerous experimental studies have promoted the idea that VDAC acts as a regulator of essential mitochondrial functions. In this study, using a combination of molecular dynamics simulations, free-energy calculations, and electrophysiological measurements, we investigated the transport of ions through VDAC, with a focus on phosphate ions and metabolites. We showed that selectivity of VDAC towards small anions including monovalent phosphates arises from short-lived interactions with positively charged residues scattered throughout the pore. In dramatic contrast, permeation of divalent phosphate ions and phosphate metabolites (AMP and ATP) involves binding sites along a specific translocation pathway. This permeation mechanism offers an explanation for the decrease in VDAC conductance measured in the presence of ATP or AMP at physiological salt concentration. The binding sites occur at similar locations for the divalent phosphate ions, AMP and ATP, and contain identical basic residues. ATP features a marked affinity for a central region of the pore lined by two lysines and one arginine of the N-terminal helix. This cluster of residues together with a few other basic amino acids forms a "charged brush" which facilitates the passage of the anionic metabolites through the pore. All of this reveals that VDAC controls the transport of the inorganic phosphates and phosphate metabolites studied here through two different mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Monophosphate / metabolism
  • Adenosine Triphosphate / metabolism
  • Binding Sites
  • Electrophysiological Phenomena
  • Ions / metabolism
  • Membrane Potential, Mitochondrial
  • Mitochondria / metabolism
  • Molecular Dynamics Simulation
  • Phosphates / metabolism*
  • Protein Structure, Tertiary
  • Thermodynamics
  • Voltage-Dependent Anion Channels / chemistry
  • Voltage-Dependent Anion Channels / metabolism*

Substances

  • Ions
  • Phosphates
  • Voltage-Dependent Anion Channels
  • Adenosine Monophosphate
  • Adenosine Triphosphate

Grants and funding

The funders of this study are the ARC grant (AUWB 2010-15-2) from the Fédération Wallonie-Bruxelles (grant number 20052), and the Fonds de la Recherche Scientifique (http://www1.frs-fnrs.be/). FH is a Research Director, MP is a Senior Research Associate, and EMK is a Postdoctoral Researcher at the Fonds de la Recherche Scientifique (F.R.S.-FNRS) (Belgium). Computational resources were provided by the Computing Centre HPC cluster, co-funded by the Université Libre de Bruxelles (ULB) and the Vrije Universiteit Brussel (VUB), the Consortium des Équipements de Calcul Intensif (CÉCI), and the Fonds de la Recherche Scientifique de Belgique (F.R.S.-F.N.R.S.) under convention 2.5020.11, together with the supercomputing facilities of the Université catholique de Louvain (CISM/UCL) and the ULB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.