Investigating metallo-peptides as antibacterial agents

Abstract

Increasing bacterial drug resistance and the emergence of dangerous resistant pathogens like methicillin-resistant Staphylococcus aureus is driving an urgent need to develop new antibiotics. Antimicrobial peptides (AMPs) and metals are two classes of antibacterial agents being explored as novel therapeutics. AMPs are produced as a part of innate immune system of living organisms and have broad spectrum activity and a bactericidal effect making bacteria less able to develop resistance., Metals are one of the oldest antibacterial agents known to humans. Notably, silver is very effective, and although its exact mode of action/s is unclear its ability to bind to a variety of enzymes is likely important. This project aims to investigate whether the coordination of silver to AMPs can create a synergistic antibacterial agent. To achieve this, AMPs, based on their potential to bind Ag(I), were selected from large AMP databases available online. Three AMPs, latarcin 3b, pleurain R1, tigerinin1, were selected. Further two Ag(I)-binding neuropeptides having properties consistent with antibacterial activity were also investigated. These were the tachykinins Neurokinin B, Substance P. Finally, Substance P was modified to include a methionine at its N-terminus (M1 Substance P) to generate a predicted high-affinity Ag(I)-binding site. The physiochemical properties of all the peptides were assessed using the R computational tool and these were related to potential antibacterial potential. Neurokinin B and Substance P have previously been shown to bind Ag(I), and the ability of the remaining peptides to coordinate Ag(I) was assessed using NMR and electronic spectroscopy. All but pleurain R1 and tigerinin1 could coordinate Ag(I), and further investigation of pleurain indicated that the lack of Ag(I)-binding was due to disulphide-bond formation. The Peptide-Ag(I) complexes were then studied for their antibacterial properties against gram negative bacteria using percentage inhibition and time-kill analysis. The results of this analysis showed that two complexes, latarcin 3b-Ag(I), and M1SP-Ag(I) displayed synergistic activity. Finally, the cellular location of silver after cultures were treated with these complexes was determined. These results show that silver alone is located mainly in the periplasm, but coordination to the peptides traps the metal in the membrane. This suggests that the synergistic effect is due to improved membrane-lytic activity. It can be concluded that the Peptide-Ag(I) complex can hold potential as next-generation antibacterial agents.

Date of Award	2018
Original language	English