1. DNA Topoisomerases
Natassja G Bush, Katherine Evans-Roberts, Anthony Maxwell EcoSal Plus. 2015;6(2). doi: 10.1128/ecosalplus.ESP-0010-2014.
DNA topoisomerases are enzymes that control the topology of DNA in all cells. There are two types, I and II, classified according to whether they make transient single- or double-stranded breaks in DNA. Their reactions generally involve the passage of a single- or double-strand segment of DNA through this transient break, stabilized by DNA-protein covalent bonds. All topoisomerases can relax DNA, but DNA gyrase, present in all bacteria, can also introduce supercoils into DNA. Because of their essentiality in all cells and the fact that their reactions proceed via DNA breaks, topoisomerases have become important drug targets; the bacterial enzymes are key targets for antibacterial agents. This article discusses the structure and mechanism of topoisomerases and their roles in the bacterial cell. Targeting of the bacterial topoisomerases by inhibitors, including antibiotics in clinical use, is also discussed.
2. Microcin 7: purification and properties
J F García-Bustos, N Pezzi, C Asensio Biochem Biophys Res Commun. 1984 Mar 15;119(2):779-85. doi: 10.1016/s0006-291x(84)80318-6.
Microcin 7 is an antibiotic peptide, produced and excreted to the culture medium by E. coli strains harboring the plasmid pRYC7. This peptide was extracted from the culture media by adsorbing it on octadecyl silica. It was purified by gel filtration on Sephadex G-25 and reverse phase high performance liquid chromatography. Its amino acid composition is the following: Ala (0.8), Arg (1.9), Asx (1.9), Gly (1.5), Met (0.8) and Thr (0.9). The purified peptide dose not react with ninhydrin and it is resistant to carboxypeptidase degradation, indicating that the molecule may be a cyclic or end-blocked oligopeptide.
3. Multifaceted ABC transporters associated to microcin and bacteriocin export
Konstantinos Beis, Sylvie Rebuffat Res Microbiol. 2019 Nov-Dec;170(8):399-406. doi: 10.1016/j.resmic.2019.07.002. Epub 2019 Aug 8.
Microcins and bacteriocins are ribosomally-synthesized defence peptides produced by Gram-negative and -positive bacteria to target competitors in their niche. Some of them carry posttranslational modifications established by dedicated enzymes. To protect themselves from their own toxic peptides, bacteria use dedicated immunity proteins or expel the toxin using ATP-binding cassette (ABC) transporters. In this last case, this immunity function is associated to export of the antimicrobial peptide out of the producing cells for targeting their competitors. Here we review the characteristics of these ABC-exporters and the mechanisms they use that unexpectedly cover from high promiscuity to high specificity or ensure another function concomitantly.
