FtsZ-Independent Mechanism of Division Inhibition by the Small Molecule PC190723 in Escherichia coli.

While cell division is a critical process in cellular proliferation, very few antibiotics have been identified that target the bacterial cell-division machinery. Recent studies have shown that the small molecule PC190723 inhibits cell division in several Gram-positive bacteria, with a hypothesized mechanism of action involving direct targeting of the tubulin homolog FtsZ, which is essential for division in virtually all bacterial species. Here, it is shown that PC190723 also inhibits cell division in the Gram-negative bacterium Escherichia coli if the outer membrane permeability barrier is compromised genetically or chemically. The results show that the equivalent FtsZ mutations conferring PC190723 resistance in Staphylococcus aureus do not protect E. coli against PC190723, and that suppressors of PC190723 sensitivity in E. coli, which do not generically decrease outer membrane permeability, do not map to FtsZ or other division proteins. These suppressors display a wide range of morphological and growth phenotypes, and one exhibits a death phenotype in the stationary phase similar to that of a mutant with disrupted lipid homeostasis. Finally, a complementing FtsZ-msfGFP fusion is used to show that PC190723 does not affect the Z-ring structure. Taken together, the findings suggest that PC190723 inhibits growth and division in E. coli without targeting FtsZ. This study highlights the importance of utilizing a combination of genetic, chemical, and single-cell approaches to dissect the mechanisms of action of new antibiotics, which are not necessarily conserved across bacterial species.

Synthesis of (±)-Bisavenanthramide B-6 by an Anionic Anhydride Mannich Reaction.

Bisavenanthramide B-6 (2) is a highly substituted γ-lactam derived from oat leaves. Development of a new base-promoted anhydride Mannich reaction with N-sulfonylated imines that forms the core structure of 2 in a single step is presented. Further elaboration allows for a facile one-pot double Buchwald N-arylation to install the final rings onto the densely substituted γ-lactam core. This route provides the natural product in a longest linear sequence of nine steps.

Targeting the Bacterial Division Protein FtsZ.

Similar to its eukaryotic counterpart, the prokaryotic cytoskeleton is essential for the structural and mechanical properties of bacterial cells. The essential protein FtsZ is a central player in the cytoskeletal family, forms a cytokinetic ring at mid-cell, and recruits the division machinery to orchestrate cell division. Cells depleted of or lacking functional FtsZ do not divide and grow into long filaments that eventually lyse. FtsZ has been studied extensively as a target for antibacterial development. In this Perspective, we review the structural and biochemical properties of FtsZ, its role in cell biochemistry and physiology, the different mechanisms of inhibiting FtsZ, small molecule antagonists (including some misconceptions about mechanisms of action), and their discovery strategies. This collective information will inform chemists on different aspects of FtsZ that can be (and have been) used to develop successful strategies for devising new families of cell division inhibitors.

Synthesis and Evaluation of Quinazolines as Inhibitors of the Bacterial Cell Division Protein FtsZ.

The bacterial cell division protein FtsZ is one of many potential targets for the development of novel antibiotics. Recently, zantrin Z3 was shown to be a cross-species inhibitor of FtsZ; however, its specific interactions with the protein are still unknown. Herein we report the synthesis of analogues that contain a more tractable core structure and an analogue with single-digit micromolar inhibition of FtsZ's GTPase activity, which represents the most potent inhibitor of Escherichia coli FtsZ reported to date. In addition, the zantrin Z3 core has been converted to two potential photo-cross-linking reagents for proteomic studies that could shed light on the molecular interactions between FtsZ and molecules related to zantrin Z3.