Host defense cationic Antimicrobial Peptides (AMPs) can kill microorganisms including bacteria, viruses and fungi using various modes of action. The negatively charged bacterial membranes serve as a key target for many AMPs. Bacterial cell death by membrane permeabilization has been well perceived. A number of cationic AMPs kill bacteria by cell agglutination which is a distinctly different mode of action compared to membrane pore formation. However, mechanism of cell agglutinating AMPs is poorly understood. The outer membrane lipopolysaccharide (LPS) or the cell-wall peptidoglycans are targeted by AMPs as a key step in agglutination process. Here, we report the first atomic-resolution structure of thanatin, a cell agglutinating AMP, in complex with LPS micelle by solution NMR. The structure of thanatin in complex with LPS, revealed four stranded antiparallel β-sheet in a ‘head-tail’ dimeric topology. By contrast, thanatin in free solution assumed an antiparallel β-hairpin conformation. Dimeric structure of thanatin displayed higher hydrophobicity and cationicity with sites of LPS interactions. MD simulations and biophysical interactions analyses provided mode of LPS recognition and perturbation of LPS micelle structures. Mechanistic insights of bacterial cell agglutination obtained in this study can be utilized to develop antibiotics of alternative mode of action.
An intelligent drug release system that is triggered into action upon sensing the motion of swarmer P. mirabilis is introduced. The rational design of the drug release system focuses on a pNIPAAm-co-pAEMA copolymer that prevents drug leakage in a tobramycin-loaded mesoporous silica particle by covering its surface via electrostatic attraction. The copolymer chains are also conjugated to peptide ligands YVLWKRKRKFCFI-NH2 that display affinity to Gram-negative bacteria. When swarmer P. mirabilis cells approach and come in contact with the particle, the copolymer-YVLWKRKRKFCFI-NH2 binds to the lipopolysaccharides on the outer membrane of motile P. mirabilis and are stripped off the particle surface when the cells move away; hence releasing tobramycin into the swarmer colony and inhibiting its expansion. The release mechanism is termed Motion-Induced Mechanical Stripping (MIMS). For swarmer B. subtilis, the removal of copolymers from particle surfaces via MIMS is not apparent due to poor adherence between bacteria and copolymer-YVLWKRKRKFCFI-NH2 system.
Linear antimicrobial peptides, with their rapid bactericidal mode of action, are well-suited for development as topical antibacterial drugs. We recently designed a synthetic linear 4-residue peptide, BRBR-NH, with potent bactericidal activity against Staphylococcus aureus (MIC 6.25 μM), the main causative pathogen of human skin infections with an unknown mechanism of action. Herein, we describe a series of experiments conducted to gain further insights into its mechanism of action involving electron microscopy, artificial membrane dye leakage, solution- and solid-state NMR spectroscopy followed by molecular dynamics simulations. Experimental results point towards a SMART (Soft Membranes Adapt and Respond, also Transiently) mechanism of action, suggesting that the peptide can be developed as a topical antibacterial agent for treating drug-resistant Staphylococcus aureus infections.
Biofilm formation by opportunistic pathogens serves as one of the major causes of chronic and persistent infections. Bacterial cells in the biofilms are embedded in their self-generated protective extracellular polymeric substances (EPS), which include exopolysaccharides, large adhesin proteins and extracellular DNA. In this study, we identified an antimicrobial peptide (AMP) LG21 that is able to interact specifically with the Psl exopolysaccharide of Pseudomonas aeruginosa, thus it can be used as a diagnostic tool for P. aeruginosa biofilms. Molecular dynamics simulation analysis showed that residues numbered from 15 to 21 (WKRKRFG) in LG21 are involved in interacting with Psl. Our study indicates that host immune systems might detect and interact with microbial biofilms through AMPs. Engineering biofilm EPS-targeting AMPs might provide novel strategies for biofilm detection and treatment.
Antimicrobial
peptides are promising molecules in uprising consequences
of drug-resistant bacteria. The prodomain of furin, a serine protease,
expressed in all vertebrates including humans, is known to be important
for physiological functions. Here, potent antimicrobial peptides were
mapped by extensive analyses of overlapping peptide fragments of the
prodomain of human furin. Two peptides, YR26 and YR23, were active
against bacterial cells including MRSA-resistant Staphylococcus
aureus and Staphylococcus epidermis 51625. Peptides were largely devoid of hemolytic and cytotoxic activity.
Bacterial cell killing occurred as a result of the disruption of the
permeability barrier of the lipopolysaccharide (LPS)-outer membrane
and fragmentation of LPS into small micelles. Furthermore, antibacterial
peptides specifically interacted with the negatively charged lipids
causing membrane leakage and fusion. The YR26 peptide in sodium dodecyl
sulfate micelles demonstrated a long-helix-turn-short-helix structure
exhibiting restricted backbone motions. The cell-selective activity
of the furin peptides and their unique mode of action on membranes
have a significant potential for the development of therapeutics.
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