Inhibition of bacterial IF2 binding to fMet-tRNA((fMet)) by aminoglycosides

Bacterial GTPases as druggable targets to tackle antimicrobial resistance

Small molecules as antibacterial agents have contributed immensely to the growth of modern medicine over the last several decades. However, the emergence of drug resistance among bacterial pathogens has undermined the effectiveness of the existing antibiotics. Thus, there is an exigency to address the antibiotic crisis by developing new antibacterial agents and identifying novel drug targets in bacteria. In this review, we summarize the importance of guanosine triphosphate hydrolyzing proteins (GTPases) as key agents for bacterial survival. We also discuss representative examples of small molecules that target bacterial GTPases as novel antibacterial agents, and highlight areas that are ripe for exploration. Given their vital roles in cell viability, virulence, and antibiotic resistance, bacterial GTPases are highly attractive antibacterial targets that will likely play a vital role in the fight against antimicrobial resistance.

In situ monitoring of structural changes during formation of 30S translation initiation complex by energy dissipation measurement using 27-MHz quartz-crystal microbalance

Ribosome is a bionanomachine that facilitates an orderly translation process during protein synthesis in living cells. Real-time monitoring of conformational changes in ribosomal subunits in aqueous solution is important to understand the regulatory mechanism of protein synthesis, because conformational changes in ribosome in E. coli have been predicted to operate the switch from translation initiation to an elongation process during translation. We performed an energy dissipation measurement by using a quartz-crystal microbalance-admittance (QCM-A) technique for in situ monitoring of conformational changes in pre-30S translation initiation complex in response to the binding of fMet-tRNA(fMet) in aqueous solution. The addition of fMet-tRNA(fMet) caused changes in the physical property (increased dehydration and elasticity) in 30S ribosomal subunit in the presence of mRNA and IF2/guanosine 5'-triphosphate (GTP) on the QCM plate. Furthermore, two sequential changes triggered by the addition of fMet-tRNA(fMet) were observed in 30S ribosomal subunit bound to mRNA in the presence of IF2/GTP and IF3. These observations suggest that the structural changes in 30S ribosomal subunit caused by the binding of fMet-tRNA(fMet) with IF2/GTP in the presence of IF3 could act as a switch to regulate the orderly processing in the construction of translation initiation complex, because the structural distinction can be a guidepost in the process for the relevant biomolecules.

Specific, efficient, and selective inhibition of prokaryotic translation initiation by a novel peptide antibiotic

Many known antibiotics target the translational apparatus, but none of them can selectively inhibit initiation of protein synthesis and/or is prokaryotic-specific. This article describes the properties of GE81112, an effective and prokaryotic-specific initiation inhibitor. GE81112 is a natural tetrapeptide produced by a Streptomyces sp. identified by an in vitro high-throughput screening test developed to find inhibitors of the prokaryotic translational apparatus preferentially acting on steps other than elongation. In vivo GE81112 inhibits protein synthesis but not other cell functions such as DNA duplication, transcription, and cell wall synthesis. In vitro GE81112 was found to target the 30S ribosomal subunit and to interfere with both coded and noncoded P-site binding of fMet-tRNA, thereby selectively inhibiting formation of the 30S initiation complex.

The Relationship between Aminoglycosides' RNA Binding Proclivity and Their Antiplasmid Effect on an IncB Plasmid

Bacteria routinely become resistant to antibiotics through the uptake of plasmids that encode resistance-mediating proteins. Such plasmid-based resistance is seen extensively in clinical settings and has been documented for a wide variety of bacterial infections from both Gram-positive and Gram-negative organisms. We recently reported that a small molecule could be used to mimic a natural process of plasmid elimination, called plasmid incompatibility, and that the addition of this compound causes elimination of an IncB plasmid from E. coli and a subsequent resensitization to antibiotics [DeNap, Thomas, Musk, and Hergenrother (2004) J. Am. Chem. Soc. 126, 15402-15404]. Described herein is a further substantiation and validation of the notion that plasmid incompatibility can be mimicked with small molecules that bind to important RNA targets controlling plasmid replication. In this study, the dissociation constant and stoichiometry of RNA binding are determined for 12 aminoglycosides with stem-loop I (SLI) of the IncB replication machinery. Importantly, it is found that compounds that do not bind to this RNA replication control element fail to induce plasmid loss in vivo, whereas those that do bind to the RNA typically cause measurable plasmid loss. These results highlight the potential for targeting key RNA regions for induction of plasmid loss and the subsequent resensitization of bacteria to antibiotics.