Helix tilt of the M2 transmembrane peptide from influenza A virus: An intrinsic property

Solid-state NMR has been used to study the influence of lipid bilayer hydrophobic thickness on the tilt of a peptide (M2-TMP) representing the transmembrane portion of the M2 protein from influenza A. Using anisotropic ¹⁵N chemical shifts as orientational constraints, single-site isotopically labeled M2-TMPs were studied in hydrated dioleoylphosphatidylcholine (DOPC) and dimyristoylphosphatidylcholine (DMPC) lipid bilayers oriented between thin glass plates. These chemical shifts provide orientational information for the molecular frame with respect to the magnetic field in the laboratory frame. When modeled as a uniform ideal α-helix, M2-TMP has a tilt of 37 (± 3)°in DMPC and 33 (± 3)°in DOPC with respect to the bilayer normal in these lipid environments. The difference in helix tilt between the two environments appears to be small. This lack of a substantial change in tilt further suggests that significant interactions occur between the helices, as in an oligomeric state, to prevent a change in tilt in thicker lipid bilayers.