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Biophys J, October 1999, p. 2102-2113, Vol. 77, No. 4
Max-Planck-Institut für-Biochemie, 82152 Martinsried, Germany
The S4 segments of voltage-gated sodium channels are
important parts of the voltage-sensing elements of these proteins.
Furthermore, the addition of the isolated S4 polypeptide to planar
lipid bilayers results in stepwise increases of ion conductivity. In
order to gain insight into the mechanisms of pore formation by
amphipathic peptides, the structure and orientation of the S4 segment
of the first internal repeat of the rat brain II sodium channel was
investigated in the presence of DPC micelles by multidimensional
solution NMR spectroscopy and solid-state NMR spectroscopy on oriented
phospholipid bilayers. Both the anisotropic chemical shift observed by
proton-decoupled 15N solid-state NMR spectroscopy and the
attenuating effects of DOXYL-stearates on TOCSY crosspeak intensities
of micelle-associated S4 indicate that the central
-helical portion
of this peptide is oriented approximately parallel to the membrane
surface. Simulated annealing and molecular dynamics calculations of the
peptide in a biphasic tetrachloromethane-water environment indicate
that the peptide
-helix extends over ~12 residues. A less regular structure further toward the C-terminus allows for the hydrophobic residues of this part of the peptide to be positioned in the
tetrachloromethane environment. The implications for possible
pore-forming mechanisms are discussed.
Biophys J, October 1999, p. 2102-2113, Vol. 77, No. 4
© 1999 by the Biophysical Society 0006-3495/99/10/2102/12 $2.00
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