Binding properties of antimicrobial agents to dipeptide terminal of lipid II using surface plasmon resonance

Characterisation of the selective binding of antibiotics vancomycin and teicoplanin by the VanS receptor regulating type A vancomycin resistance in the enterococci

A-type resistance towards "last-line" glycopeptide antibiotic vancomycin in the leading hospital acquired infectious agent, the enterococci, is the most common in the UK. Resistance is regulated by the VanRASA two-component system, comprising the histidine sensor kinase VanSA and the partner response regulator VanRA. The nature of the activating ligand for VanSA has not been identified, therefore this work sought to identify and characterise ligand(s) for VanSA. In vitro approaches were used to screen the structural and activity effects of a range of potential ligands with purified VanSA protein. Of the screened ligands (glycopeptide antibiotics vancomycin and teicoplanin, and peptidoglycan components N-acetylmuramic acid, D-Ala-D-Ala and Ala-D-y-Glu-Lys-D-Ala-D-Ala) only glycopeptide antibiotics vancomycin and teicoplanin were found to bind VanSA with different affinities (vancomycin 70μM; teicoplanin 30 and 170μM), and were proposed to bind via exposed aromatic residues tryptophan and tyrosine. Furthermore, binding of the antibiotics induced quicker, longer-lived phosphorylation states for VanSA, proposing them as activators of type A vancomycin resistance in the enterococci.

Hydrodynamics of the VanA-type VanS histidine kinase: an extended solution conformation and first evidence for interactions with vancomycin

VanA-type resistance to glycopeptide antibiotics in clinical enterococci is regulated by the VanSARA two-component signal transduction system. The nature of the molecular ligand that is recognised by the VanSA sensory component has not hitherto been identified. Here we employ purified, intact and active VanSA membrane protein (henceforth referred to as VanS) in analytical ultracentrifugation experiments to study VanS oligomeric state and conformation in the absence and presence of vancomycin. A combination of sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge (SEDFIT, SEDFIT-MSTAR and MULTISIG analysis) showed that VanS in the absence of the ligand is almost entirely monomeric (molar mass M = 45.7 kDa) in dilute aqueous solution with a trace amount of high molar mass material (M ~ 200 kDa). The sedimentation coefficient s suggests the monomer adopts an extended conformation in aqueous solution with an equivalent aspect ratio of ~(12 ± 2). In the presence of vancomycin over a 33% increase in the sedimentation coefficient is observed with the appearance of additional higher s components, demonstrating an interaction, an observation consistent with our circular dichroism measurements. The two possible causes of this increase in s - either a ligand induced dimerization and/or compaction of the monomer are considered.

Surface mediated cooperative interactions of drugs enhance mechanical forces for antibiotic action

The alarming increase of pathogenic bacteria that are resistant to multiple antibiotics is now recognized as a major health issue fuelling demand for new drugs. Bacterial resistance is often caused by molecular changes at the bacterial surface, which alter the nature of specific drug-target interactions. Here, we identify a novel mechanism by which drug-target interactions in resistant bacteria can be enhanced. We examined the surface forces generated by four antibiotics; vancomycin, ristomycin, chloroeremomycin and oritavancin against drug-susceptible and drug-resistant targets on a cantilever and demonstrated significant differences in mechanical response when drug-resistant targets are challenged with different antibiotics although no significant differences were observed when using susceptible targets. Remarkably, the binding affinity for oritavancin against drug-resistant targets (70 nM) was found to be 11,000 times stronger than for vancomycin (800 μM), a powerful antibiotic used as the last resort treatment for streptococcal and staphylococcal bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Using an exactly solvable model, which takes into account the solvent and membrane effects, we demonstrate that drug-target interactions are strengthened by pronounced polyvalent interactions catalyzed by the surface itself. These findings further enhance our understanding of antibiotic mode of action and will enable development of more effective therapies.

Surface Plasmon Resonance Assay of Binding Properties of Antisense Oligonucleotides to Serum Albumins and Lipoproteins

In the present study, we developed an assay to evaluate the kinetic binding properties of the unconjugated antisense oligonucleotide (ASO) and lipophilic and hydrophilic ligands conjugated ASOs to mouse and human serum albumin, and lipoproteins using surface plasmon resonance (SPR). The lipophilic ligands conjugated ASOs showed clear affinity to the albumins and lipoproteins, while the unconjugated and hydrophilic ligand conjugated ASOs showed no interaction. The SPR method showed reproducible immobilization of albumins and lipoproteins as ligands on the sensor chip, and reproducible affinity kinetic parameters of interaction of ASOs conjugated with the ligands could be obtained. The kinetic binding data of these ASOs to albumin and lipoproteins by SPR were related with the distributions in the whole liver in mice after administration of these conjugated ASOs. The results demonstrated that our SPR method could be a valuable tool for predicting the mechanism of the properties of delivery of conjugated ASOs to the organs.

Antimicrobial Activity of Plectasin NZ2114 in Combination with Cell Wall Targeting Antibiotics Against VanA-Type Enterococcus faecalis

Antimicrobial peptide plectasin targeting bacterial cell wall precursor Lipid II has been reported to be active against benzylpenicillin-resistant Streptococcus pneumoniae but less potent against vancomycin-resistant enterococci than their susceptible counterparts. The aim of this work was to test plectasin NZ2114 in combination with cell wall targeting antibiotics on vancomycin-resistant Enterococcus faecalis. The activity of antibiotic combinations was evaluated against VanA-type vancomycin-resistant E. faecalis strain BM4110/pIP816-1 by disk agar-induction, double-disk assay, determination of fractional inhibitory concentration (FIC) index, and time-kill curve. The results indicated that plectasin NZ2114 was synergistic in combination with teicoplanin, moenomycin, and dalbavancin but not with vancomycin, telavancin, penicillin G, bacitracin, ramoplanin, daptomycin, and fosfomycin. To gain an insight into the synergism, we tested other cell wall antibiotic combinations. Interestingly, synergy was observed between teicoplanin or moenomycin and the majority of the antibiotics tested; however, vancomycin was only synergistic with penicillin G. Other cell wall active antibiotics such as ramoplanin, bacitracin, and fosfomycin did not synergize. It appeared that most of the synergies observed involved inhibition of the transglycosylation step in peptidoglycan synthesis. These results suggest that teicoplanin, dalbavancin, vancomycin, and telavancin, although they all bind to the C-terminal D-Ala-D-Ala of Lipid II, might act on different stages of cell wall synthesis.