Structural changes in the model of the outer cell membrane of Gram-negative bacteria interacting with melittin: An in situ spectroelectrochemical study
A cell membrane of Gram-negative bacteria interacting with an antimicrobial peptide represents a complex supramolecular assembly. Fabrication of the models of bacterial cell membranes remains a large experimental challenge. Langmuir-Blodgett and Langmuir-Schaefer (LS-LB) transfer enables deposition of multicomponent asymmetric lipid bilayers onto a gold surface. In this work 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and di [3-deoxy-D-manno-octulosonyl]-lipid A (KLA) are used to fabricate a model of the outer membrane of Gram-negative bacteria. Molecular scale changes in the model membrane exposed to physiological electric fields interacting with melittin antimicrobial peptide are examined. Interaction of the outer membrane with melittin leads to an increase in membrane capacitance and permeability to ions and water. At positive membrane potential the stability of the outer membrane with bound melittin decreases. In situ polarization modulation infrared reflection absorption spectroscopy is used to investigate membrane potential-dependent changes in the structure of the outer membrane interacting with melittin. The hydration of the polar head groups is not affected by the interaction with melittin. However, the orientation and hydrogen bond network to the carboxylate groups in KLA changes drastically after POPE-KLA bilayer interaction with melittin. Positively charged groups at the C-terminus of the peptide interact directly with the polar head group of KLA. The N-terminus enters into the hydrophobic region of the membrane and forms a channel to the hydrophilic head groups in POPE, in the inner leaflet. The electrostatic interactions between the N-terminus and the inner side of the bilayer are stabilized at negative membrane potentials. The packing order in hydrocarbon chains in the membrane with bound melittin increases. It is associated with hydrophobic matching between the chains in lipids and the peptide which spans the membrane.
- This article is part of the themed collection: Peptide-membrane interactions