Structure and dynamics of fluid nanofilms: study of peptide-membrane interactions with classical and new techinques

DUPUY, FERNANDO G.

Sao Paulo

Congreso; 28th Annual User Meeting (RAU); 2018

Centro Nacional de Pesquisa em Energia e Materiais

Bacterial cell membranes are important target fornew antimicrobial strategies based on amphipathic peptides because occurrenceof resistance is slower than in protein based targets. Knowing structuraldetails of peptide-membrane interactions is of utmost importance forunderstanding the mechanism of action of antimicrobial peptides, as nonbilayerstructures can arise when bilayers encounter peptides and as a result, pores orcarpeting are formed. Even though antimicrobial peptides have been studied intensivelyin the last years, there?s still lacking a molecular view of the dynamics andstructural determinants of bacterial bilayer destabilization. In this regard, xray scattering techniques provide information on the lipid phase and itstridimentional dimensions in biologically relevant aqueous dilutions. Westudied membrane model systems resembling Gram positive and Gram negativebacterial cells and their interaction with antimicrobial peptides enterocinCRL35 and microcin J25 active against Listeria and Escherichia colicells, respectively. Our methods included x ray scattering at small angle inliquid samples at different temperatures consisting in liposomes made of PG andPE at different proportions according to the model coincubated with peptides a20:1 lipid:peptide ratio. The results indicated that control samples formeduncorrelated bilayers due to repulsive forces of the negatively charged lipidsbut in the presence of peptides, correlated bilayers and even non-bilayersstructures are formed. By using oriented multilamellar stacks of membranes, wealso studied how mechanical properties of lipid bilayers at full hydration arechanged by measuring diffuse x ray scattering at grazing incidance, applyingliquid crystal theory for calculating bending moduli Kc. The two techniquesprovide useful complementary information for understanding molecular detailsand dynamics of the mechanism of action of antimicrobials in membranes.