How do the mechanical properties of the membrane affect the activity of an antimicrobial peptide?

FELSZTYNA, IVÁN; WILKE, NATALIA

Córdoba

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofísica; 2023

Sociedad Argentina de Biofísica

Antimicrobial peptides (AMPs) are biosynthesized by many classes of organisms as part oftheir immune response. Most of the AMPs act through the disruption of lipid membranes.Because of their positive net charges, AMPs tend to interact preferentially with thenegatively charged bacterial membranes, being this the most accepted reason for theselectivity of these peptides to the target membranes. In particular, MP1 is an AMPextracted from the brazilian wasp Polybia paulista. It presents a broad spectrum activity,without being hemolytic. MP1 has a low positive net charge (+2) in comparison to otherAMPs, suggesting that its selectivity could be only marginally based on electrostaticinteractions, but more related to other membrane properties. With the aim ofunderstanding how the membrane mechanical properties influence MP1 activity, weconducted experiments on model membranes composed of zwitterionicphosphatidylcholine lipids with varying chain lengths, unsaturation degree and phasestates. Carboxyfluorescein (CF) leakage experiments performed on large unilamellarvesicles (LUVs) showed that the phase state was determinant for membrane permeation.LUVs in the fluid phase were permeated at low peptide/lipid (P/L) ratios, while no effectwas observed in the gel phase. In addition, unsaturated LUVs showed CF leakage at higherP/L ratios than the saturated ones. Size measurements by dynamic light scatteringindicated that saturated LUVs in the fluid phase were disrupted at P/L ratios depending onthe chain length. In unsaturated LUVs, their size was polydisperse even at low P/L ratios. Inthe gel phase, no effects in vesicle size were observed. Given that previous experimentsshowed that the maximum insertion surface pressures for MP1 in DMPC and DPPCmonolayers were around 30 mN/m, the absence of effects in the gel phase could becaused by a lack of adsorption/insertion to the bilayer. Future studies evaluatingtryptophan fluorescence will allow us to confirm this observation.