Marsh D, Jost M, Peggion C, Toniolo C.Lipid chain-length
dependence for incorporation of alamethicin in membranes:
electron paramagnetic resonance studies on TOAC-spin labeled
analogs.
Biophys J. 2007 Jun 1;92(11):4002-11. Epub 2007 Mar 9.
Max-Planck-Institut für biophysikalische Chemie, Abteilung
Spektroskopie, 37070 Göttingen, Germany.
dmarsh@gwdg.de
Alamethicin is a 19-residue hydrophobic peptide, which is
extended by a C-terminal phenylalaninol but lacks residues that
might anchor the ends of the peptide at the lipid-water
interface. Voltage-dependent ion channels formed by alamethicin
depend strongly in their characteristics on chain length of the
host lipid membranes. EPR spectroscopy is used to investigate
the dependence on lipid chain length of the incorporation of
spin-labeled alamethicin in phosphatidylcholine bilayer
membranes. The spin-label amino acid TOAC is substituted at
residue positions n = 1, 8, or 16 in the sequence of alamethicin
F50/5 [TOAC(n), Glu(OMe)(7,18,19)]. Polarity-dependent isotropic
hyperfine couplings of the three TOAC derivatives indicate that
alamethicin assumes approximately the same location, relative to
the membrane midplane, in fluid diC(N)PtdCho bilayers with chain
lengths ranging from N = 10-18. Residue TOAC(8) is situated
closest to the bilayer midplane, whereas TOAC(16) is located
farther from the midplane in the hydrophobic core of the
opposing lipid leaflet, and TOAC(1) remains in the lipid polar
headgroup region. Orientational order parameters indicate that
the tilt of alamethicin relative to the membrane normal is
relatively small, even at high temperatures in the fluid phase,
and increases rather slowly with decreasing chain length (from
13 degrees to 23 degrees for N = 18 and 10, respectively, at 75
degrees C). This is insufficient for alamethicin to achieve
hydrophobic matching. Alamethicin differs in its mode of
incorporation from other helical peptides for which
transmembrane orientation has been determined as a function of
lipid chain length.
PMID: 17351010
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