The minor groove-binding agent ELB-21 forms multiple interstrand and intrastrand covalent cross-links with duplex DNA and displays potent bactericidal activity against methicillin-resistant Staphylococcus aureus

OBJECTIVES: The antistaphylococcal pyrrolobenzodiazepine dimer ELB-21 forms multiple adducts with duplex DNA through covalent interactions with appropriately spaced guanine residues; it is now known to form interstrand and intrastrand adducts with oligonucleotide sequences of variable length. We determined the DNA sequence preferences of ELB-21 in relation to its capacity to exert a bactericidal effect by damaging DNA. METHODS: Formation of adducts by ELB-21 and 12- to 14-mer DNA duplexes was investigated using ion-pair reversed phase liquid chromatography and mass spectrometry. Drug-induced changes in gene expression were measured in prophage-free Staphylococcus aureus RN4220 by microarray analysis. RESULTS: ELB-21 preferentially formed intrastrand adducts with guanines separated by three nucleotide base pairs. Interstrand and intrastrand adducts were formed with duplexes both longer and shorter than the preferred target sequences. ELB-21 elicited rapid bactericidal effects against prophage-carrying and prophage-free S. aureus strains; cell lysis occurred following activation and release of resident prophages. Killing appeared to be due to irreparable damage to bacterial DNA and susceptibility to ELB-21 was governed by the capacity of staphylococci to repair DNA lesions through induction of the SOS DNA damage response mediated by the RecA-LexA pathway. CONCLUSIONS: The data support the contention that ELB-21 arrests DNA replication, eliciting formation of ssDNA-RecA filaments that inactivate LexA, the SOS repressor, and phage repressors such as Cl, resulting in activation of the DNA damage response and de-repression of resident prophages. Above the MIC threshold, DNA repair is ineffective

Antistaphylococcal activity of DNA-interactive pyrrolobenzodiazepine (PBD) dimers and PBD-biaryl conjugates

Objectives: pyrrolobenzodiazepine (PBD) dimers, tethered through inert propyldioxy or pentyldioxy linkers, possess potent bactericidal activity against a range of Gram-positive bacteria by virtue of their capacity to cross-link duplex DNA in sequence-selective fashion. Here we attempt to improve the antibacterial activity and cytotoxicity profile of PBD-containing conjugates by extension of dimer linkers and replacement of one PBD unit with phenyl-substituted or benzo-fused heterocycles that facilitate non-covalent interactions with duplex DNA.Methods: DNase I footprinting was used to identify high-affinity DNA binding sites. A staphylococcal gene microarray was used to assess epidemic methicillin-resistant Staphylococcus aureus 16 phenotypes induced by PBD conjugates. Molecular dynamics simulations were employed to investigate the accommodation of compounds within the DNA helix.Results: increasing the length of the linker in PBD dimers led to a progressive reduction in antibacterial activity, but not in their cytotoxic capacity. Complex patterns of DNA binding were noted for extended PBD dimers. Modelling of DNA strand cross-linking by PBD dimers indicated distortion of the helix. A majority (26 of 43) of PBD-biaryl conjugates possessed potent antibacterial activity with little or no helical distortion and a more favourable cytotoxicity profile. Bactericidal activity of PBD-biaryl conjugates was determined by inability to excise covalently bound drug molecules from bacterial duplex DNA.Conclusions: PBD-biaryl conjugates have a superior antibacterial profile compared with PBD dimers such as ELB-21. We have identified six PBD-biaryl conjugates as potential drug development candidate

In vivo Lokalisations- und Interaktionsstudien der Sensorkinase KdpD aus Escherichia coli

In dieser Arbeit konnten mittels des BACTH-Systems Interaktionen des kompletten KdpD Proteins sowie der N-terminalen Domäne (KdpD1-395) mit den N- und C-terminalen (KdpD396-894) Domänen von KdpD nachgewiesen werden. Darüber hinaus wurde der Zusammenhang zwischen dem Interaktionsverhalten und den Phänotypen bestimmter Punktmutations- und Deletionsmutanten von KdpD untersucht, jedoch konnte eine solche Abhängigkeit nicht bestätigt werden. Die Lokalisation von KdpD-GFP wurde in dem kdpD-Teildeletionsstamm TKV2208 untersucht, in dem sich das Hybridprotein membrangebunden in einem gepunkteten Verteilungsmuster entlang des Zellkörpers nachweisen lässt. Besonders interessant ist das häufige Vorkommen spiralförmiger KdpD-GFP Strukturen, welche sich entlang des Zellkörpers zeigen. Daher wurde eine Beeinflussung der Lokalisation von KdpD-GFP durch MreB vermutet. Eine Behandlung der Zellen mit der Verbindung A22 veränderte die Proteinverteilung jedoch nicht. Daher ist anzunehmen, dass die KdpD-GFP Lokalisation in E. coli MreB-unabhängig erfolgt. Des Weiteren wurde eine Beeinflussung der Lokalisation des Hybridproteins durch das Penicillin-Bindeprotein 3 in Erwägung gezogen. Um diese Möglichkeit zu evaluieren wurde PBP3 mit Cephalexin spezifisch gehemmt. Jedoch konnte kein Unterschied zur vorher aufgeführten Lokalisation von KdpD-GFP beobachtet werden. Ein weiterer Aspekt der Lokalisationsstudien war, ob Cardiolipin einen Einfluss auf die KdpD-GFP Lokalisation hat. Für diese Fragestellung wurde der Stamm UE54 benutzt, welcher kein Cardiolipin synthetisieren kann. Es konnte gezeigt werden, dass Cardiolipin keinen Einfluss auf die Lokalisation von KdpD-GFP zu haben scheint. Darüber hinaus wurde die Abhängigkeit der KdpD-GFP Lokalisation von SecB und SecG mittels Deletionsmutanten getestet. Die Deletion dieser beiden Sec-Translokationsproteine führte jedoch zu keiner Veränderung der Lokalisation von KdpD-GFP

Maltose and Maltodextrin Utilization by Bacillus subtilis

Bacillus subtilis can utilize maltose and maltodextrins that are derived from polysaccharides, like starch or glycogen. In this work, we show that maltose is taken up by a member of the phosphoenolpyruvate-dependent phosphotransferase system and maltodextrins are taken up by a maltodextrin-specific ABC transporter. Uptake of maltose by the phosphoenolpyruvate-dependent phosphotransferase system is mediated by maltose-specific enzyme IICB (MalP; synonym, GlvC), with an apparent K(m) of 5 μM and a V(max) of 91 nmol · min(−1) · (10(10) CFU)(−1). The maltodextrin-specific ABC transporter is composed of the maltodextrin binding protein MdxE (formerly YvdG), with affinities in the low micromolar range for maltodextrins, and the membrane-spanning components MdxF and MdxG (formerly YvdH and YvdI, respectively), as well as the energizing ATPase MsmX. Maltotriose transport occurs with an apparent K(m) of 1.4 μM and a V(max) of 4.7 nmol · min(−1) · (10(10) CFU)(−1)