Interactions of human β-defensin 28 with solid supports mimicking bacterial and mammalian cell membranes

Development of resistance to conventional antibiotics by several bacterial strains is on the rise. To address this issue, antimicrobial peptides (AMPs) have recently proposed as alternatives to conventional antibiotics. Beside their excellent antimicrobial performance, these new antibiotics have less susceptibility to bacterial resistance development, making them safe and effective alternatives. Thus, this work presents a quantitative study on the interactions of human β-defensin 28 (an antimicrobial peptide) with bacterial-like (POPG-terminated) and mammalian-like (POPC-terminated) bilayer membranes. The first leaflet of both membranes was created through the self-assembly of thiolipid (TL) on the gold surface of a surface plasmon resonance (SPR) sensor chip. The second membrane leaflet was created by the fusion of either 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1-rac-glycerol) (abbreviated as POPG) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (abbreviated as POPC) phospholipid on the TL layer. The binding kinetics of human β-defensin 28 (hBD28) onto POPG and POPC surfaces were investigated. The surface saturation (Γ_max) and affinity (K_a) of hBD28 for the POPG surface were estimated to be 4.51 ± 0.12 mg m⁻² and 0.12 ± 0.01 mL μg⁻¹, respectively. However, Γ_max and K_a of the peptide (i.e., hBD28) for POPC surface were much lower: 1.65 mg m⁻² and 0.03 mL μg⁻¹, respectively. These findings suggest that hBD28 is reasonably selective towards pathogen-like membranes (i.e., POPG). hBD28 was also found to form an acceptably stable coating (via adsorption) on hydrophobic (TL) and negatively charged hydrophilic (11-mercaptoundecanoic acid, abbreviated as MUA) surfaces. The surface concentrations of the peptide on the TL and MUA surfaces at saturation were estimated to be 3.82 ± 0.32 and 4.47 ± 0.25 mg m⁻², while its affinities for those surfaces were estimated to be 0.14 ± 0.05 and 0.13 ± 0.03 mL μg⁻¹, respectively.