Stella L, Burattini M, Mazzuca C, Palleschi A, Venanzi M, Coin
I, Peggion C, Toniolo C, Pispisa B.Alamethicin interaction
with lipid membranes: a spectroscopic study on synthetic
analogues.
Chem Biodivers. 2007 Jun;4(6):1299-312.
Dipartimento di Scienze e Tecnologie Chimiche, Università di
Roma Tor Vergata, Rome, Italy.
stella@stc.uniroma2.it
Alamethicin (Alm) is one of the most extensively studied
membrane-active antibiotic peptides, but several aspects of its
mechanism of action are still under debate. In this study,
synthetic analogues of natural Alm F50/5 (Alm-N), labeled with a
9H-fluoren-9-yl group at the N- (F-Alm) or C-terminus (Alm-F),
were employed to investigate the position and orientation of
this peptide in the membrane environment. Depth-dependent
fluorescence quenching and polarized ATR-FT-IR experiments
demonstrated that, in the absence of a transmembrane potential,
Alm inserts its N-terminus into the membrane, while the
C-terminus is exposed to the outer aqueous phase. We also found
that the peptaibol populates different orientations with respect
to the membrane normal. Furthermore, fluorescence
resonance-energy transfer (FRET) indicated that no peptide
translocation to the inner leaflet of lipid bilayers occurs. The
mechanism of action of Alm is discussed on the basis of these
findings.Two other Alm analogues, Alm-P and Alm-S, were
exploited to investigate the role of specific Alm residues in
terms of membrane-perturbing activity. Substitution of two or
three Gln (E) residues (the only polar amino acids in the
alamethicin sequence) by gamma-methyl glutamate (Glu(OMe))
residues induced marked variations in the aggregation and
partition behaviors of the peptaibols, which, in turn, modulate
their membrane activity. In particular, substitution of Gln(18)
and Gln(19) caused a six-fold increase in membrane-perturbing
activity, thus demonstrating that these residues are not
essential for the stabilization of Alm pores.
PMID: 17589867
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