Optical Methods Elucidating Action of Antimicrobial Peptides

Interaction with biological membranes plays a key role in the activity of antimicrobial peptides (AMPs). We study changes in supported phospholipid bilayers (SPBs), a model of biological membranes, induced by cryptdin-4 (Crp-4), an AMP with β-sheet structure, and compare those interactions with those of magainin 2, a prototypical α-helical AMP. We are using a combination of complementary experimental techniques: laser scanning microscopy (LSM), ellipsometry and fluorescence correlation spectroscopy (FCS), and electronegative SPB (DOPC/DOPS 4/1). Results of LSM and ellipsometry show that Crp-4 causes much less perturbations to the bilayer than magainin 2, which induces a large loss of lipids. Crp-4 slows down the diffusion of lipids within the bilayer (FCS results), which can mean increased rigidity or formation of obstacles to the diffusion (e.g. small discrete pores).