Interaction of Anionic Antimicrobial Peptides with Model Membranes

MM NOE; JA RODRIGUEZ; GR BARREDO VACCHELLI; SA CAMPERI; MA PERILLO; MV NOLAN

Rosario

Congreso; L Reunión Anual de la Sociedad Argentina de Biofísica; 2022

Sociedad Argentina de Biofísica

Anionic antimicrobial peptides (AAP) were first reported in the early 1980s. They havebeen established as part of the innate immune systems of vertebrates, invertebrates andplants, and they are active against bacteria, fungi, viruses and pests such as insects.Membrane interaction appears key to the antimicrobial function of AAMPs. In the presentwork we use the anionic peptide β-lg125-135 that is obtained from tryptic hydrolysate of β-lactoglobulin and evaluate its interaction with model membranes. We use DPPC orDPPC:DPPG equimolar mixture as a model of eukaryotic or bacterial membrane,respectively. The interaction of the anionic peptide with monolayers of differentcomposition was examined at different initial surface pressures (πi) by measuring thevariation in surface pressure after peptide injection in the subphace as a function of timeuntil reaching a plateau (πmax). The plot (πmax- πi) vs πi allows determining the maximumπ at which the peptide modifies the membrane molecular packing (through binding orinsertion) (πcut-off). Results obtained shown a πcut-off = 45,7mN/m and 22,3mN/m fordpPC:dpPG and dpPC monolayers, respectively, suggesting that β-lg125-135 interactsstrongly with anionic interfaces. Furthermore, the kinetics of β-lg125-135 – monolayerinteraction was determined from π vs. time plots at a fixed πi and diferent peptideconcentration in the subphase under a lipid monolayer. It allowed determine the peptidemonolayerassociation (ka) and dissociation (kd) rate constants and the thermodynamicassociation binding constant (Ka). The values obtained demonstrated that although theassociation and dissociation kinetics of β-lg125-135 to the dpPC:dpPG film was faster thanthat for DPPC, the β-lg125-135 - DPPC interaction affinity resulted the strongest.Changes in the peptide secondary structure induced by membrane interaction werestudied by circular dichroism and infrared spectroscopy. Using both techniques we foundthat, in solution the peptide structure was mainly disordered, with some residues probablyin α-helix conformation. No significant changes were found in the presence of lipidmembranes.