Magic Angle Spinning and Oriented Sample Solid State NMR Structural Restraints Combine for Influenza A M2 Protein Functional Insights

摘要

As a small tetrameric helical membrane protein, the M2 proton channel structure is highly sensitive to its environment. As a result, structural data from a lipid bilayer environment has proven to be essential for describing the conductance mechanism. While oriented sample solid state NMR has provided a high resolution backbone structure in lipid bilayers, quaternary packing of the helices and many of the sidechain conformations have been poorly restrained. Furthermore, an understanding of the quaternary structural stability has remained a mystery. Here, the isotropic chemical shift data and interhelical cross peaks from magic angle spinning solid state NMR of a liposomal preparation strongly support the quaternary structure of the transmembrane helical bundle as a dimer of dimers structure. The data also explains how the tetrameric stability is enhanced once two charges are absorbed by the His37 tetrad prior to activation of this proton channel. The combination of these two solid state NMR techniques appear to be a powerful approach for characterizing helical membrane protein structure.