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Biophys. J. BioFAST: First Published February 18, 2005. doi:10.1529/biophysj.104.056077
© 2005 by the Biophysical Society.

A more recent version of this article appeared on May 1, 2005.
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Lorenzo Stella
Mariano Venanzi
Basilio Pispisa
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MEMBRANES

Mechanism of Membrane Activity of the Antibiotic Trichogin GA IV: a Two-state Transition Controlled by Peptide Concentration

Claudia Mazzuca 1, Lorenzo Stella 1, Mariano Venanzi 1, Fernando Formaggio 2, Claudio Toniolo 2 and Basilio Pispisa 1*

1 Universitá di Roma Tor Vergata
2 Universitá di Padova

* To whom correspondence should be addressed. E-mail: pispisa{at}stc.uniroma2.it.

Submitted on November 15, 2004
Revised on January 23, 2005
Accepted on 4 February 2005


  Abstract
Synthetic fluorescent analogues of the natural lipopeptide trichogin GA IV were used to investigate the peptide position and orientation in model membranes. A translocation assay based on Förster energy transfer indicates that trichogin is associated to both the outer and inner leaflet of the membrane, even at low concentration, when it is not active. Fluorescence quenching measurements, performed by using water soluble quenchers and quenchers positioned in the membrane at different depths, indicate that at low membrane-bound peptide to lipid ratios trichogin lies close to the region of polar headgroups. By increasing peptide concentration until membrane leakage takes place, a cooperative transition occurs and a significant fraction of the peptide becomes deeply buried into the bilayer. Remarkably, this change in peptide position is strictly coupled with peptide aggregation. Therefore, the mechanism of trichogin action can be envisaged as based on a two-state transition controlled by peptide concentration. One state is the monomeric, surface bound and inactive peptide, and the other state is a buried, aggregated form, which is responsible for membrane leakage and bioactivity.

Key Words: depth-dependent quenching, fluorescence spectroscopy, peptide aggregation, peptide-membrane interactions, pore formation, resonance energy transfer




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Copyright © 2005 by the Biophysical Society.