The alignment of a voltage-sensing peptide in dodecylphosphocholine micelles and in oriented lipid bilayers by nuclear magnetic resonance and molecular modeling

The S4 segments of voltage-gated sodium channels are important parts of the voltage-sensing elements of these proteins. Furthermore, the addition of t he isolated S4 polypeptide to planar lipid bilayers results in stepwise inc reases of ion conductivity. In order to gain insight into the mechanisms of pore formation by amphipathic peptides, the structure and orientation of t he S4 segment of the first internal repeat of the rat brain II sodium chann el was investigated in the presence of DPC micelles by multidimensional sol ution NMR spectroscopy and solid-state NMR spectroscopy on oriented phospho lipid bilayers. Both the anisotropic chemical shift observed by proton-deco upled N-15 solid-state NMR spectroscopy and the attenuating effects of DOXY L-stearates on TOCSY crosspeak intensities of micelle-associated S4 indicat e that the central ct-helical portion of this peptide is oriented approxima tely parallel to the membrane surface. Simulated annealing and molecular dy namics calculations of the peptide in a biphasic tetrachloromethane-water e nvironment indicate that the peptide ct-helix extends over similar to 12 re sidues. A less regular structure further toward the C-terminus allows for t he hydrophobic residues of this part of the peptide to be positioned in the tetrachloromethane environment. The implications for possible pore-forming mechanisms are discussed.