Analysis of antimicrobial peptide interactions with hybrid bilayer membrane systems using surface plasmon resonance

The lipid binding behaviour of the antimicrobial peptides magainin 1, melittin and the C-terminally truncated analogue of melittin (21Q) was studied with a hybrid bilayer membrane system using surface plasmon resonance. In particular, the hydrophobic association chip was used which is composed of long chain alkanethiol molecules upon which liposomes adsorb spontaneously to create a hybrid bilayer membrane surface. Multiple sets of sensorgrams with different peptide concentrations were generated. Linearisation analysis and curve fitting using numerical integration analysis were performed to derive estimates for the association (k(a)) and dissociation (k(d)) rate constants. The results demonstrated that magainin 1 preferentially interacted with negatively charged dimyristoyl-L-alpha-phosphatidyl-DL-glycerol (DMPG), while melittin interacted with both zwitterionic dimyristoyl-L-alpha-phosphatidylcholine and anionic DMPG. In contrast, the C-terminally truncated melittin analogue, 21Q, exhibited lower binding affinity for both lipids, showing that the positively charged C-terminus of melittin greatly influences its membrane binding properties. Furthermore the results also demonstrated that these antimicrobial peptides bind to the lipids initially via electrostatic interactions which then enhances the subsequent hydrophobic binding. The biosensor results were correlated with the conformation of the peptides determined by circular dichroism analysis, which indicated that high alpha-helicity was associated with high binding affinity. Overall, the results demonstrated that biosensor technology provides a new experimental approach to the study of peptide-membrane interactions through the rapid determination of the binding affinity of bioactive peptides for phospholipids.