Rimantadine Binds to and Inhibits the Influenza A M2 Proton Channel without Enantiomeric Specificity

Jessica L. Thomaston, Marley L. Samways, Athina Konstantinidi, Chunlong Ma, Yanmei Hu, Hannah E. Bruce Macdonald, Jun Wang, Jonathan W. Essex, William F. Degrado, Antonios Kolocouris

Abstract

The influenza A M2 wild-type (WT) proton channel is the target of the anti-influenza drug rimantadine. Rimantadine has two enantiomers, though most investigations into drug binding and inhibition have used a racemic mixture. Solid-state NMR experiments using the full length-M2 WT have shown significant spectral differences that were interpreted to indicate tighter binding for (R)- vs (S)-rimantadine. However, it was unclear if this correlates with a functional difference in drug binding and inhibition. Using X-ray crystallography, we have determined that both (R)- and (S)-rimantadine bind to the M2 WT pore with slight differences in the hydration of each enantiomer. However, this does not result in a difference in potency or binding kinetics, as shown by similar values for kon, koff, and Kd in electrophysiological assays and for EC50 values in cellular assays. We concluded that the slight differences in hydration for the (R)- and (S)-rimantadine enantiomers are not relevant to drug binding or channel inhibition. To further explore the effect of the hydration of the M2 pore on binding affinity, the water structure was evaluated by grand canonical ensemble molecular dynamics simulations as a function of the chemical potential of the water. Initially, the two layers of ordered water molecules between the bound drug and the channel's gating His37 residues mask the drug's chirality. As the chemical potential becomes more unfavorable, the drug translocates down to the lower water layer, and the interaction becomes more sensitive to chirality. These studies suggest the feasibility of displacing the upper water layer and specifically recognizing the lower water layers in novel drugs.

Original languageEnglish (US)
Pages (from-to)2471-2482
Number of pages12
JournalBiochemistry
Volume60
Issue number32
DOIs
StatePublished - Aug 17 2021

ASJC Scopus subject areas

  • Biochemistry

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