Jessica Steigenberger

Abstract

Our general interest is to understand the mode of action of membrane-active peptides, drugs, and other molecules that interfere with the transport or barrier functions of membranes.

My specific attention is dedicated to cyclic lipopeptides (CLiP), produced by Pseudomonas spp., which show plant beneficial and antimicrobial properties acting presumably by perturbing cellular membranes.

In general, the membrane perturbing activity of a compound involves a two-step process depending on (i) its affinity to bind to the membrane and (ii) the damage done by a membrane-inserted molecule, i.e., how poorly the compound harmonizes with the structure and dynamics of the lipid bilayer (“molecular disharmony”). A typical dose-response function does not distinguish between these contributions and since the membrane-bound fraction depends on the absolute lipid concentration, it is only valid at this lipid concentration, even if plotted versus the peptide-to-lipid ratio.

We aim at telling binding apart from disharmony contributions to dose-response curves. This will improve our biophysical understanding of membrane permeabilization and shall provide a much better insight into the mode of action and interactions governing lipid selectivity, aiding a more rational optimization of new antibiotics and pesticides.

Therefore, we measure CLiP induced membrane permeabilization as a function of lipid composition and lipid concentration utilizing time-correlated single-photon counting experiments of calcein self-quenching in liposomes. Moreover, we investigate the effects of molecular charge and acyl chain length of CLiPs on affinity and disharmony contributions.

Methods

• Microcalorimetry (DSC, IMC, ITC)
• Time-correlated single-photon counting
• Dynamic light scattering