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Updated: Oct 2, 2026
Co-immunoprecipitation of the Mouse Mx1 Protein with the Influenza A Virus Nucleoprotein
Published on: April 21, 2015
Permeation and activation of the M2 ion channel of influenza A virus
J A Mould1, J E Drury, S M Frings
1Department of Neurobiology and Physiology and the Department of Biochemistry, Molecular Biology, and Cell Biology, Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois 60208-3500, USA.
Abstract:
The M(2) ion channel protein of influenza A virus is essential for mediating protein-protein dissociation during the virus uncoating process that occurs when the virus is in the acidic environment of the lumen of the secondary endosome. The difficulty of determining the ion selectivity of this minimalistic ion channel is due in part to the fact that the channel activity is so great that it causes local acidification in the expressing cells and a consequent alteration of reversal voltage, V(rev). We have confirmed the high proton selectivity of the channel (1.5-2.0 x 10(6)) in both oocytes and mammalian cells by using four methods as follows: 1) comparison of V(rev) with proton equilibrium potential; 2) measurement of pH(in) and V(rev) while Na(+)(out) was replaced; 3) measurements with limiting external buffer concentration to limit proton currents specifically; and 4) comparison of measurements of M(2)-expressing cells with cells exposed to a protonophore. Increased currents at low pH(out) are due to true activation and not merely increased [H(+)](out) because increased pH(out) stops the outward current of acidified cells. Although the proton conductance is the biologically relevant conductance in an influenza virus-infected cell, experiments employing methods 1-3 show that the channel is also capable of conducting NH(4)(+), probably by a different mechanism from H(+).
Insights
The M2 ion channel of influenza A virus is highly proton-selective, crucial for viral uncoating. Researchers confirmed this selectivity using four methods, also finding it conducts ammonium ions.
Area of Science:
- Virology
- Ion Channel Physiology
- Molecular Biology
Background:
- The M2 protein of influenza A virus forms a proton-selective ion channel essential for viral uncoating.
- Determining the M2 channel's ion selectivity is challenging due to its high activity causing local cellular acidification and altered reversal voltage (Vrev).
Purpose of the Study:
- To confirm the high proton selectivity of the M2 ion channel.
- To investigate the M2 channel's conductance properties beyond protons.
Main Methods:
- Utilized four distinct electrophysiological methods to assess M2 channel ion selectivity in oocytes and mammalian cells.
- Methods included comparing reversal voltage (Vrev) with proton equilibrium potential, manipulating external sodium concentrations, limiting external buffer capacity, and comparing M2-expressing cells with protonophore-treated cells.
Main Results:
- Confirmed high proton selectivity of the M2 channel, with a selectivity ratio of 1.5-2.0 x 10^6.
- Demonstrated that increased currents at low external pH are due to channel activation, not just increased proton concentration.
- Showed that the M2 channel can conduct ammonium ions (NH4+), likely through a distinct mechanism compared to proton conduction.
Conclusions:
- The M2 ion channel exhibits significant proton selectivity, consistent with its biological role in influenza virus uncoating.
- While proton conductance is biologically dominant, the M2 channel possesses the capacity for ammonium ion transport.
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