Interactions between the aspartic acid-rich antimicrobial peptide D4 and model membranes

The anionic antimicrobial peptide D4 (D-D-D-D-OH) was previously shown to be bactericidal for Pasteurella Haemolytica in the presence of zinc saline solution. This study focuses on the effect of zinc and copper ions on the ability of D4 to bind to DPPC and DMPC model membranes in acidic medium. Dynamic light scattering (DLS), thermogravimetric analysis (TGA), infrared (IR), and scanning electron microscopy (SEM) techniques are employed. FTIR with FT self-deconvolution, second derivative resolution enhancement methods, and curve-fitting procedures were applied for quantitative analysis of peptide conformation variations. The quantitative analysis indicated that D4 adopts mainly an alpha-helix structure. Upon metal addition, a major reduction of the &agr;-helix structure was observed, with Cu inducing beta-sheet and turn structures. Zinc induced beta-sheet structures. D4 strongly interacts with DPPC and DMPC in the presence of zinc and copper. The interaction with DPPC and DMPC is stronger in the presence of zinc than in the presence of copper. DLS data showed that Zn-D4 complex is smaller than Cu-D4 complex, while TGA data indicated that Zn-D4 complex is more thermally stable than Cu-D4 complex. SEM images revealed that zinc-D4 complex has a fiber-like morphology, which makes it a promising candidate for "bioinspired" materials.