Transport mechanisms of SARS-CoV-E viroporin in calcium solutions: Lipid-dependent Anomalous Mole Fraction Effect and regulation of pore conductance

Biochim Biophys Acta Biomembr. 2021 Jun 1;1863(6):183590. doi: 10.1016/j.bbamem.2021.183590. Epub 2021 Feb 20.

Abstract

The envelope protein E of the SARS-CoV coronavirus is an archetype of viroporin. It is a small hydrophobic protein displaying ion channel activity that has proven highly relevant in virus-host interaction and virulence. Ion transport through E channel was shown to alter Ca2+ homeostasis in the cell and trigger inflammation processes. Here, we study transport properties of the E viroporin in mixed solutions of potassium and calcium chloride that contain a fixed total concentration (mole fraction experiments). The channel is reconstituted in planar membranes of different lipid compositions, including a lipid mixture that mimics the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) membrane where the virus localizes within the cell. We find that the E ion conductance changes non-monotonically with the total ionic concentration displaying an Anomalous Mole Fraction Effect (AMFE) only when charged lipids are present in the membrane. We also observe that E channel insertion in ERGIC-mimic membranes - including lipid with intrinsic negative curvature - enhances ion permeation at physiological concentrations of pure CaCl2 or KCl solutions, with a preferential transport of Ca2+ in mixed KCl-CaCl2 solutions. Altogether, our findings demonstrate that the presence of calcium modulates the transport properties of the E channel by interacting preferentially with charged lipids through different mechanisms including direct Coulombic interactions and possibly inducing changes in membrane morphology.

Keywords: Calcium regulation; Electrophysiology; Ion channel; Lipid-protein interactions; Transport mechanisms; Viroporin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Calcium / metabolism*
  • Calcium Channels / metabolism
  • Ion Transport
  • Membrane Lipids / metabolism
  • Protein Binding
  • Protein Transport
  • Severe acute respiratory syndrome-related coronavirus / metabolism*
  • Solutions
  • Viroporin Proteins / chemistry
  • Viroporin Proteins / metabolism*

Substances

  • Calcium Channels
  • Membrane Lipids
  • Solutions
  • Viroporin Proteins
  • Calcium