Solid-State NMR Study on the Conductance Mechanism and Acid Activation of M2 Proton Channel

Abstract

M2 is a 97-residue, single-pass membrane protein which functions in a tetrameric state. The tetramer forms a proton channel which has been proven to be a drug target for Influenza A virus (H3N2 and H1N1). However, the M2 protein of this virus has recently mutated so that the anti-flu drugs, amantadine and rimantadine are no longer effective; consequently there is increased urgency to define the structure and functional mechanism of this protein as an aid for drug development. Even though it has long been believed that M2 protein is a proton channel with a high selectivity, most functional assays find a low conductance rate which resembles the activity of a transporter. An atomistic mechanism has recently been proposed for the proton transport involving the His37 and Trp41 residues in this tetramer [1]. Here we present magic angle spinning solid state NMR spectroscopic data of the M2(22-62) construct and the full-length protein that bear on this mechanistic model and on the pH-induced structural changes. Solid state NMR provides an opportunity to characterize the protein in a native-like lipid bilayer environment. Recently, a comparison of M2 transmembrane domain structures obtained from detergent and lipid bilayer environments has demonstrated the importance of using good models of the membrane environment [2].[1] M. Sharma, M. Yi, H. Dong, H. Qin, E. Peterson, D. D. Busath, H.-X. Zhou, and T. A. Cross (2010). Insight into the mechanism of the influenza A proton channel from a structure in a lipid bilayer. Science (in press).[2] T. A. Cross, M. Sharma, M. Yi, and H.-X. Zhou (2010). Influence of solubilizing environments on membrane protein structures. Trends Biochem. Sci. (in press).