Activation pH and Gating Dynamics of Influenza A M2 Proton Channel Revealed by Single‐Molecule Spectroscopy

• Published in: Angewandte Chemie International Edition 2017-05, Vol.56 (19), p.5283-5287
• Main Authors: Lin, Chun‐Wei, Mensa, Bruk, Barniol‐Xicota, Marta, DeGrado, William F., Gai, Feng
• Format: Article
• Language: English
• Subjects: conformational dynamics; Electron Transport; fluorescence correlation spectroscopy; Fluorescent Dyes - chemistry; Hydrogen-Ion Concentration; Influenza A virus; M2 proton channels; Orthomyxoviridae; pH titration; Photochemical Processes; photoinduced electron transfer; Protein Conformation; Spectrometry, Fluorescence; Thermodynamics; Viral Matrix Proteins - chemistry; Viral Matrix Proteins - metabolism
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201701874

Because of its importance in viral replication, the M2 proton channel of the influenza A virus has been the focus of many studies. Although we now know a great deal about the structural architecture underlying its proton conduction function, we know little about its conformational dynamics, especially those controlling the rate of this action. Herein, we employ a single‐molecule fluorescence method to assess the dynamics of the inter‐helical channel motion of both full‐length M2 and the transmembrane domain of M2. The rate of this motion depends not only on the identity of the channel and membrane composition but also on the pH in a sigmoidal manner. For the full‐length M2 channel, the rate is increased from approximately 190 μs−1 at high pH to approximately 80 μs−1 at low pH, with a transition midpoint at pH 6.1. Because the latter value is within the range reported for the conducting pKa value of the His37 tetrad, we believe that this inter‐helical motion accompanies proton conduction. Motion of the gate: The Trp41 gate of the M2 proton channel is shown to undergo a spontaneous conformational motion on a timescale of tens to hundreds of microseconds. The time constant of this motion exhibits a sigmoidal dependence on pH with a midpoint that closely matches the electrophysiologically determined conducting pKa value of the His37 tetrad, suggesting that this motion accompanies proton conduction.