The Gate of the Influenza Virus M2 Proton Channel Is Formed by a Single Tryptophan Residue

Yajun Tang,Florina Zaitseva,Robert A Lamb,Lawrence H Pinto

doi:10.1074/jbc.m206582200

Yajun Tang, Florina Zaitseva + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m206582200

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Abstract

The influenza virus M2 proton-selective ion channel is known to be essential for acidifying the interior of virions during virus uncoating in the lumen of endosomes. The M2 protein is a homotetramer that contains four 19-residue transmembrane (TM) domains. These TM domains are multifunctional, because they contain the channel pore and also anchor the protein in membranes. The M2 protein is gated by pH, and thus we have measured pH-gated currents, the accessibility of the pore to Cu2+, and the effect of a protein-modifying reagent for a series of TM domain mutant M2 proteins. The results indicate that gating of the M2 ion channel is governed by a single side chain at residue 41 of the TM domain and that this property is mediated by an indole moiety. Unlike many ion channels where the gate is formed by a whole segment of a protein, our data suggest a model of striking simplicity for the M2 ion channel protein, with the side chain of Trp(41) blocking the pore of the M2 channel when pH(out) is high and with this side chain leaving the pore when pH(out) is low. Thus, the Trp(41) side chain acts as the gate that opens and closes the pore.

Highlights

The prediction that the influenza A virus M2 protein has a proton-selective ion channel activity (Refs. 1 and 2 and reviewed in Ref. 3) arose from a coupling of various observations on the life cycle of influenza virus
The influenza virus M2 protein is a model of minimalism because it has only a single multifunctional TM domain, which contains the pore of the channel (25), acts both to target the protein initially to the membrane of the rough endoplasmic reticulum (ER) and anchor the protein in the ER membrane (61), and, as we show here, contains the activation gate
To identify the region of the M2 ion channel protein that serves as its activation gate and to assess the extent to which the M2 ion channel gate was open, oocytes of X. laevis expressing the M2 protein were used

Summary

Introduction

The prediction that the influenza A virus M2 protein has a proton-selective ion channel activity (Refs. 1 and 2 and reviewed in Ref. 3) arose from a coupling of various observations on the life cycle of influenza virus. To test the possibility that Trp[41] acts as the channel gate, mutant proteins containing residues at position 41 with less bulky side chains were examined for outward current.

Results

Conclusion