Selective assembly and insertion of ubiquicidin antimicrobial peptide in lipid monolayers

Antimicrobial-resistant bacteria pose a significant threat to humans, prompting extensive research into developing new antimicrobial peptides (AMPs). The biomembrane is the first barrier of a biological cell, hence, comprehending the interaction and self-assembly of AMPs in and around such membranes is of great importance. In the present study, several biophysical techniques have been applied to explore the self-assembly of ubiquicidin (29–41), an archetypical AMP, in and around the phospholipid monolayers formed at air–water interface. Such a monolayer mimics one of the leaflets of a lipid bilayer. The surface pressure–area isotherm exhibits the strongest interaction with a negatively charged lipid, 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (sodium salt) (DPPG). The weakest affinity was towards the zwitterionic lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Another zwitterionic lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), shows an intermediate affinity. This affinity was quantified by analyzing alterations in the effective mean molecular area of the lipid, the in-plane compressional modulus of the assembly, and the electrostatic potential induced by the presence of peptides. The precise organization of the peptide around the lipid monolayer at a sub-nanometre length scale was revealed using synchrotron-based X-ray reflectivity measurements from the air–water interface. Information about the selective interaction of the peptide with lipids and their varied orientation at the lipid–water interface could be useful in understanding the selectivity of AMP in developing new antibiotics.