Solid-state NMR characterization of conformational plasticity within the transmembrane domain of the influenza A M2 proton channel

Membrane protein function within the membrane interstices is achieved by mechanisms that are not typically available to water-soluble proteins. The whole balance of molecular interactions that stabilize three-dimensional structure in the membrane environment is different from that in an aqueous environment. As a result interhelical interactions are often dominated by non-specific van der Waals interactions permitting dynamics and conformational heterogeneity in these interfaces. Here, solid-state NMR data of the transmembrane domain of the M2 protein from influenza A virus are used to exemplify such conformational plasticity in a tetrameric helical bundle. Such data lead to very high resolution structural restraints that can identify both subtle and substantial structural differences associated with various states of the protein. Spectra from samples using two different preparation protocols, samples prepared in the presence and absence of amantadine, and spectra as a function of pH are used to illustrate conformational plasticity.