Interfacial Behaviors of Antimicrobial Peptide Cecropin P1 Immobilized on Different Self-Assembled Monolayers
Qiuming Wang, Shuai Wei, Jianfeng Wu, Xingquan Zou, Olivia Sieggreen, Yuwei Liu, Chuanwu Xi, Charles L. Brooks III, Zhan Chen
The Journal of Physical Chemistry C
Surfaces immobilized with biological molecules such as peptides and proteins are widely used in many important applications including biosensors, medical devices, and food packaging. It was found that the structures of surface-immobilized peptides control their surface properties. In this study, we investigated interfacial behaviors of antimicrobial peptide cecropin P1 (CP1) immobilized onto a maleimide-terminated self-assembled monolayer (Mal SAM) and a mixed SAM (Mal-OH SAM, a mixture of maleimide-terminated SAM and hydroxyl-terminated SAM) surface via C-terminus modified cysteine (CP1c). The surface coverage, secondary structure, orientation, and antimicrobial activity of immobilized CP1c were investigated using surface plasmon resonance (SPR), circular dichroism (CD), sum frequency generation (SFG) vibrational spectroscopy, dynamic contact antimicrobial assay, and coarse grained molecular dynamics (MD) simulations. It was found that the surface coverages of CP1c on the Mal SAM and the mixed Mal-OH SAM are similar. CP1c on Mal SAM possessed a dominant helical structure with a single orientation of ∼32° versus surface normal. CP1c on Mal-OH mixed SAM surface also possessed a dominant helical structure but with multiple orientations. MD simulation results can be correlated to the experimental data: the simulation results indicate a narrow distribution of orientations of CP1c immobilized on Mal SAM, but multiple orientations are sampled on the more hydrophilic Mal-OH SAM. Even though the surface orientations of CP1c immobilized on the two SAM surfaces are different, activity against both Gram-negative and Gram-positive bacteria (Escherichia coli and Staphylococcus aureus) exhibited similar results for CP1c immobilized on both SAM surfaces. We believe that this is because the antimicrobial activity of the surface-immobilized peptides is mainly affected by the electrostatic interactions between the strong basic N-terminal residues and the negatively charged bacteria cell wall/cell membrane.
Circular dichroism, Secondary structure, Biochemistry