Poster Presentation 2014 International Biophysics Congress

Probing the interaction dynamics between a model antimicrobial peptide and giant unilamellar vesicles (#310)

Matthew G. Burton 1 , Qi M. Huang 1 , M. Akhter Hossain 2 , John D. Wade 2 , Andrew H.A. Clayton 3 , Michelle L. Gee 1
  1. School of Chemistry, University of Melbourne, Parkville, VIC, Australia
  2. Florey Department of Neuroscience and Mental Health, Centre for Neuroscience Research Chemistry, University of Melbourne, Parkville, VIC, Australia
  3. Centre for Micro-Photonics, Swinburne University of Technology, Hawthorn, VIC, Australia

In this work, the interaction dynamics between a lytic peptide and a biomembrane was studied using time-lapse fluorescence lifetime imaging microscopy. The model membrane was pure phospholipid giant unilamellar vesicles (GUVs), and the peptide was a K14 derivative of melittin, to which the polarity-sensitive fluorescent probe AlexaFluor 430 was grafted. Based on previous photophysics characterization of the peptide, we were able to deconvolve the contribution of three distinct peptide states to the lifetime trajectory, and then use this data to develop a kinetics model for the peptide-membrane interaction. It was found that the interaction process resulted in progressive quenching of the fluorescence lifetime over a period of minutes. This interaction could be well described by a two-step mechanism: peptide monomer adsorption followed by membrane surface migration, assembly, and insertion to form membrane pores. In contrast to previous studies, there was no evidence of critical behavior; irrespective of the lipid/peptide (L/P) concentration ratio, lytic pores were the dominant peptide state at equilibrium, and were formed even at very low peptide concentrations. Furthermore, there was an equilibrium exchange between pore and surface monomers at all L/P ratios studied, indicating attainment of a fully inserted phase. We suggest that this behavior is seen in GUVs because their low curvature means low Laplace pressure. Membrane elasticity is therefore relatively ineffective at damping the thermal fluctuations of lipid molecules that lead to random molecular-level lipid protrusions and membrane undulations. The resultant localised, transient membrane deformations thus create the conditions necessary for facile peptide insertion.