Effects of pH and ionic strength on the assembly and bundling of FtsZ protofilaments: A possible role of electrostatic interactions in the bundling of protofilaments

Lateral interactions between protofilaments of the bacterial tubulin homolog FtsZ are essential for cell division

The prokaryotic tubulin homolog FtsZ polymerizes into protofilaments, which further assemble into higher-order structures at future division sites to form the Z-ring, a dynamic structure essential for bacterial cell division. The precise nature of interactions between FtsZ protofilaments that organize the Z-ring and their physiological significance remain enigmatic. In this study, we solved two crystallographic structures of a pair of FtsZ protofilaments, and demonstrated that they assemble in an antiparallel manner through the formation of two different inter-protofilament lateral interfaces. Our in vivo photocrosslinking studies confirmed that such lateral interactions occur in living cells, and disruption of the lateral interactions rendered cells unable to divide. The inherently weak lateral interactions enable FtsZ protofilaments to self-organize into a dynamic Z-ring. These results have fundamental implications for our understanding of bacterial cell division and for developing antibiotics that target this key process.

WhmD promotes the assembly of Mycobacterium smegmatis FtsZ: A possible role of WhmD in bacterial cell division

WhmD is considered to have a role in the septation and division of Mycobacterium smegmatis cells. Since FtsZ is the central protein of the septum, we determined the effect of WhmD on the assembly of Mycobacterium smegmatis FtsZ (MsFtsZ) in vitro. WhmD increased both the rate and extent of the assembly of MsFtsZ in vitro. WhmD also increased the amount of polymerized MsFtsZ as evident from a sedimentation assay. Further, the assembly promoting activity of WhmD occurred in the presence of GTP. MsFtsZ polymerized to form thin filaments in the absence of WhmD while MsFtsZ formed thick filaments in the presence of WhmD suggesting that WhmD enhanced the bundling of MsFtsZ filaments. Interestingly, WhmD neither suppressed the dilution-induced disassembly of FtsZ filaments nor significantly altered the GTPase activity of FtsZ. Using size exclusion chromatography, circular dichroism and fluorescence spectroscopy, WhmD was found to bind to MsFtsZ in vitro. The results showed that WhmD can promote the assembly of FtsZ and indicated that WhmD may play a role in the division of M. smegmatis cells by assisting the polymerization of FtsZ.

Doxorubicin inhibits E. coli division by interacting at a novel site in FtsZ

The increase in antibiotic resistance has become a major health concern in recent times. It is therefore essential to identify novel antibacterial targets as well as discover and develop new antibacterial agents. FtsZ, a highly conserved bacterial protein, is responsible for the initiation of cell division in bacteria. The functions of FtsZ inside cells are tightly regulated and any perturbation in its functions leads to inhibition of bacterial division. Recent reports indicate that small molecules targeting the functions of FtsZ may be used as leads to develop new antibacterial agents. To identify small molecules targeting FtsZ and inhibiting bacterial division, we screened a U.S. FDA (Food and Drug Administration)-approved drug library of 800 molecules using an independent computational, biochemical and microbial approach. From this screen, we identified doxorubicin, an anthracycline molecule that inhibits Escherichia coli division and forms filamentous cells. A fluorescence-binding assay shows that doxorubicin interacts strongly with FtsZ. A detailed biochemical analysis demonstrated that doxorubicin inhibits FtsZ assembly and its GTPase activity through binding to a site other than the GTP-binding site. Furthermore, using molecular docking, we identified a probable doxorubicin-binding site in FtsZ. A number of single amino acid mutations at the identified binding site in FtsZ resulted in a severalfold decrease in the affinity of FtsZ for doxorubicin, indicating the importance of this site for doxorubicin interaction. The present study suggests the presence of a novel binding site in FtsZ that interacts with the small molecules and can be targeted for the screening and development of new antibacterial agents.

Bacterial cell division proteins as antibiotic targets

Proteins involved in bacterial cell division often do not have a counterpart in eukaryotic cells and they are essential for the survival of the bacteria. The genetic accessibility of many bacterial species in combination with the Green Fluorescence Protein revolution to study localization of proteins and the availability of crystal structures has increased our knowledge on bacterial cell division considerably in this century. Consequently, bacterial cell division proteins are more and more recognized as potential new antibiotic targets. An international effort to find small molecules that inhibit the cell division initiating protein FtsZ has yielded many compounds of which some are promising as leads for preclinical use. The essential transglycosylase activity of peptidoglycan synthases has recently become accessible to inhibitor screening. Enzymatic assays for and structural information on essential integral membrane proteins such as MraY and FtsW involved in lipid II (the peptidoglycan building block precursor) biosynthesis have put these proteins on the list of potential new targets. This review summarises and discusses the results and approaches to the development of lead compounds that inhibit bacterial cell division.

Polioviral receptor binding ligand: a novel and safe peptide drug carrier from polioviral capsid

Cellular uptake enhancement of green fluorescent protein (GFP) into human colon adenocarcinoma (HT-29) and human mouth epidermal carcinoma (KB) cells by a segment of VP1-BC loop polioviral capsid (V), a polioviral receptor binding peptide and HIV-I transactivator of transcription (Tat) was evaluated. HT-29 and KB cells were incubated with various molar concentrations of GFP, V, and Tat mixtures. Both V and Tat showed potent enhancement of GFP uptake into HT-29 and KB cells. In HT-29 cells, the V-GFP, Tat-GFP, and V-Tat-GFP mixtures enhanced the GFP cellular uptake efficiency with the maximum of 3.98-, 4.59-, and 4.08-folds of GFP at 1:3, 1:1/6, and 1/6:1:1/6 molar ratios, respectively. For KB cells, the V-GFP, Tat-GFP, and V-Tat-GFP mixtures enhanced the GFP cellular uptake efficiency with the maximum of 4.05-, 5.09-, and 4.91-folds of GFP at 1:1/6, 1:1, and 1:1:1 molar ratios, respectively. Both V and V-GFP mixtures showed a lower cytotoxicity effect than Tat and Tat-GFP mixture. These studies demonstrated the potential of polioviral capsid, a polioviral receptor binding peptide as a novel, low cytotoxicity carrier for the development of peptide drugs delivery system.

ZipA binds to FtsZ with high affinity and enhances the stability of FtsZ protofilaments

A bacterial membrane protein ZipA that tethers FtsZ to the membrane is known to promote FtsZ assembly. In this study, the binding of ZipA to FtsZ was monitored using fluorescence spectroscopy. ZipA was found to bind to FtsZ with high affinities at three different (6.0, 6.8 and 8.0) pHs, albeit the binding affinity decreased with increasing pH. Further, thick bundles of FtsZ protofilaments were observed in the presence of ZipA under the pH conditions used in this study indicating that ZipA can promote FtsZ assembly and stabilize FtsZ polymers under unfavorable conditions. Bis-ANS, a hydrophobic probe, decreased the interaction of FtsZ and ZipA indicating that the interaction between FtsZ and ZipA is hydrophobic in nature. ZipA prevented the dilution induced disassembly of FtsZ polymers suggesting that it stabilizes FtsZ protofilaments. Fluorescein isothiocyanate-labeled ZipA was found to be uniformly distributed along the length of the FtsZ protofilaments indicating that ZipA stabilizes FtsZ protofilaments by cross-linking them.

Strong FtsZ is with the force: mechanisms to constrict bacteria

FtsZ, the best-known prokaryotic division protein, assembles at midcell with other proteins forming a ring during septation. Widely conserved in bacteria, FtsZ represents the ancestor of tubulin. In the presence of GTP it forms polymers able to associate into multi-stranded flexible structures. FtsZ research is aimed at determining the role of the Z-ring in division, describing the polymerization and potential force-generating mechanisms and evaluating the roles of nucleotide exchange and hydrolysis. Systems to reconstruct the FtsZ ring in vitro have been described and some of its mechanical properties have been reproduced using in silico modeling. We discuss current research in FtsZ, some of the controversies, and finally propose further research needed to complete a model of FtsZ action that reconciles its in vitro properties with its role in division.

Promoting assembly and bundling of FtsZ as a strategy to inhibit bacterial cell division: a new approach for developing novel antibacterial drugs

FtsZ plays an essential role in bacterial cell division. We have used the assembly of FtsZ as a screen to find antibacterial agents with a novel mechanism of action. The effects of 81 compounds of 29 different structural scaffolds on FtsZ assembly in vitro were examined using a sedimentation assay. Out of these 81 compounds, OTBA (3-{5-[4-oxo-2-thioxo-3-(3-trifluoromethyl-phenyl)-thiazolidin-5-ylidenemethyl]-furan-2-yl}-benzoic acid) was found to promote FtsZ assembly in vitro. OTBA increased the assembly of FtsZ, caused bundling of FtsZ protofilaments, prevented dilution-induced disassembly of FtsZ protofilaments and decreased the GTPase activity in vitro. It bound to FtsZ with an apparent dissociation constant of 15±1.5 μM. Furthermore, OTBA inhibited the proliferation of Bacillus subtilis 168 cells with an MIC (minimum inhibitory concentration) of 2 μM, whereas it exerted minimal effects on mammalian cell proliferation, indicating that it might have a potential use as an antibacterial drug. In the effective proliferation inhibitory concentration range, OTBA induced filamentation in bacteria and also perturbed the formation of the cytokinetic Z-rings in bacteria. However, the agent neither perturbed the membrane structures nor affected the nucleoid segregation in B. subtilis cells. The results suggested that the OTBA inhibited bacterial cytokinesis by perturbing the formation and functioning of the Z-ring via altering FtsZ assembly dynamics. The antibacterial mechanism of action of OTBA is similar to that of the widely used anticancer drug paclitaxel, which inhibits cancer cell proliferation by promoting the assembly of tubulin, a eukaryotic homologue of FtsZ.

Structural and functional model for ionic (K(+)/Na(+)) and pH dependence of GTPase activity and polymerization of FtsZ, the prokaryotic ortholog of tubulin

Bacterial cell division occurs through the formation of a protein ring (division ring) at the site of division, with FtsZ being its main component in most bacteria. FtsZ is the prokaryotic ortholog of eukaryotic tubulin; it shares GTPase activity properties and the ability to polymerize in vitro. To study the mechanism of action of FtsZ, we used molecular dynamics simulations of the behavior of the FtsZ dimer in the presence of GTP-Mg(2+) and monovalent cations. The presence of a K(+) ion at the GTP binding site allows the positioning of one water molecule that interacts with catalytic residues Asp235 and Asp238, which are also involved in the coordination sphere of K(+). This arrangement might favor dimer stability and GTP hydrolysis. Contrary to this, Na(+) destabilizes the dimer and does not allow the positioning of the catalytic water molecule. Protonation of the GTP gamma-phosphate, simulating low pH, excludes both monovalent cations and the catalytic water molecule from the GTP binding site and stabilizes the dimer. These molecular dynamics predictions were contrasted experimentally by analyzing the GTPase and polymerization activities of purified Methanococcus jannaschii and Escherichia coli FtsZ proteins in vitro.