PEPTIDE ORIENTATION IN LIPID BILAYERS STUDIED BY ORIENTED CIRCULAR DICHROISM SPECTROSCOPY

Antimicrobial peptides (AMPs) are biomolecules involved in the innate immune response of a wide range of organisms, exhibiting strong inhibitory activity against the growth of bacteria, fungi, and viruses. Their mechanism of action is directly associated with interactions with biological membranes, involving membrane adsorption, structural reorganization, insertion into the lipid bilayer, and, in some cases, pore formation. Despite their considerable biotechnological and pharmacological potential, many aspects concerning the spatial orientation and molecular organization of these peptides within membranes remain poorly understood. Here, the orientation of cationic AMPs from the Temporin and Plantaricin families in lipid bilayers is being investigated by Oriented Circular Dichroism (OCD) spectroscopy, enabling the evaluation of the preferential alignment of the peptide helix with respect to the membrane plane. Lipid chain length and peptide net charge were shown to effectively modulate peptide orientation within the membrane. Peptides were incorporated at different peptide-to-lipid molar ratios. The systems were characterized by both conventional Circular Dichroism (CD) and Oriented Circular Dichroism (OCD) spectroscopy, and helix tilt was correlated with membrane composition, hydration level, and lipid acyl chain length. These insights are expected to contribute to a fundamental understanding of AMP mechanisms of action and support the rational design of novel antimicrobial agents.