The prokaryotic cytoskeleton: a putative target for inhibitors and antibiotics?

Measuring the stiffness of bacterial cells from growth rates in hydrogels of tunable elasticity

Although bacterial cells are known to experience large forces from osmotic pressure differences and their local microenvironment, quantitative measurements of the mechanical properties of growing bacterial cells have been limited. We provide an experimental approach and theoretical framework for measuring the mechanical properties of live bacteria. We encapsulated bacteria in agarose with a user-defined stiffness, measured the growth rate of individual cells and fit data to a thin-shell mechanical model to extract the effective longitudinal Young's modulus of the cell envelope of Escherichia coli (50-150 MPa), Bacillus subtilis (100-200 MPa) and Pseudomonas aeruginosa (100-200 MPa). Our data provide estimates of cell wall stiffness similar to values obtained via the more labour-intensive technique of atomic force microscopy. To address physiological perturbations that produce changes in cellular mechanical properties, we tested the effect of A22-induced MreB depolymerization on the stiffness of E. coli. The effective longitudinal Young's modulus was not significantly affected by A22 treatment at short time scales, supporting a model in which the interactions between MreB and the cell wall persist on the same time scale as growth. Our technique therefore enables the rapid determination of how changes in genotype and biochemistry affect the mechanical properties of the bacterial envelope.

Targeting the assembly of bacterial cell division protein FtsZ with small molecules

FtsZ is the key protein of bacterial cell division and an emergent target for new antibiotics. It is a filament-forming GTPase and a structural homologue of eukaryotic tubulin. A number of FtsZ-interacting compounds have been reported, some of which have powerful antibacterial activity. Here we review recent advances and new approaches in modulating FtsZ assembly with small molecules. This includes analyzing their chemical features, binding sites, mechanisms of action, the methods employed, and computational insights, aimed at a better understanding of their molecular recognition by FtsZ and at rational antibiotic design.

Clostridial binary toxins: iota and C2 family portraits

There are many pathogenic Clostridium species with diverse virulence factors that include protein toxins. Some of these bacteria, such as C. botulinum, C. difficile, C. perfringens, and C. spiroforme, cause enteric problems in animals as well as humans. These often fatal diseases can partly be attributed to binary protein toxins that follow a classic AB paradigm. Within a targeted cell, all clostridial binary toxins destroy filamentous actin via mono-ADP-ribosylation of globular actin by the A component. However, much less is known about B component binding to cell-surface receptors. These toxins share sequence homology amongst themselves and with those produced by another Gram-positive, spore-forming bacterium also commonly associated with soil and disease: Bacillus anthracis. This review focuses upon the iota and C2 families of clostridial binary toxins and includes: (1) basics of the bacterial source; (2) toxin biochemistry; (3) sophisticated cellular uptake machinery; and (4) host–cell responses following toxin-mediated disruption of the cytoskeleton. In summary, these protein toxins aid diverse enteric species within the genus Clostridium.

Targeting the Wolbachia cell division protein FtsZ as a new approach for antifilarial therapy

The use of antibiotics targeting the obligate bacterial endosymbiont Wolbachia of filarial parasites has been validated as an approach for controlling filarial infection in animals and humans. Availability of genomic sequences for the Wolbachia (wBm) present in the human filarial parasite Brugia malayi has enabled genome-wide searching for new potential drug targets. In the present study, we investigated the cell division machinery of wBm and determined that it possesses the essential cell division gene ftsZ which was expressed in all developmental stages of B. malayi examined. FtsZ is a GTPase thereby making the protein an attractive Wolbachia drug target. We described the molecular characterization and catalytic properties of Wolbachia FtsZ. We also demonstrated that the GTPase activity was inhibited by the natural product, berberine, and small molecule inhibitors identified from a high-throughput screen. Furthermore, berberine was also effective in reducing motility and reproduction in B. malayi parasites in vitro. Our results should facilitate the discovery of selective inhibitors of FtsZ as a novel anti-symbiotic approach for controlling filarial infection. NOTE: The nucleotide sequences reported in this paper are available in GenBank™ Data Bank under the accession number wAlB-FtsZ (JN616286).

Fungal lectin of Peltigera canina induces chemotropism of compatible Nostoc cells by constriction-relaxation pulses of cyanobiont cytoskeleton

A glycosylated arginase acting as a fungal lectin from Peltigera canina is able to produce recruitment of cyanobiont Nostoc cells and their adhesion to the hyphal surface. This implies that the cyanobiont would develop organelles to motility towards the chemoattractant. However when visualized by transmission electron microscopy, Nostoc cells recently isolated from P. canina thallus do not reveal any motile, superficial organelles, although their surface was covered by small spindles and serrated layer related to gliding. The use of S-(3,4-dichlorobenzyl)isothiourea, blebbistatin, phalloidin and latrunculin A provide circumstantial evidence that actin microfilaments rather than MreB, the actin-like protein from prokaryota, and, probably, an ATPase which develops contractile function similar to that of myosin II, are involved in cell motility. These experimental facts, the absence of superficial elements (fimbriae, pili or flagellum) related to cell movement, and the appearance of sunken cells during of after movement verified by scanning electron microscopy, support the hypothesis that the motility of lichen cyanobionts could be achieved by contraction-relaxation episodes of the cytoskeleton induced by fungal lectin act as a chemoattractant.

Chemical-biological studies of subcellular organization in bacteria

The subcellular organization of biological molecules is a critical determinant of many bacterial processes, including growth, replication of the genome, and division, yet the details of many mechanisms that control intracellular organization remain unknown. Decoding this information will impact the field of bacterial physiology and can provide insight into eukaryotic biology, including related processes in mitochondria and chloroplasts. Small molecule probes provide unique advantages in studying these mechanisms and manipulating the organization of biomolecules in live bacterial cells. In this review, we describe small molecules that are available for investigating subcellular organization in bacteria, specifically targeting FtsZ, MreB, peptidoglycan, and lipid bilayers. We discuss how these probes have been used to study microbiological questions and conclude by providing suggestions about important areas in which chemical-biological approaches will have a revolutionary impact on the study of bacterial physiology.

A combined global and local approach to elucidate spatial organization of the Mycobacterial ParB-parS partition assembly

Combining diverse sets of data at global (size, shape) and local (residue) scales is an emerging trend for elucidating the organization and function of the cellular assemblies. We used such a strategy, combining data from X-ray and neutron scattering with H/D-contrast variation and X-ray footprinting with mass spectrometry, to elucidate the spatial organization of the ParB-parS assembly from Mycobacterium tuberculosis. The ParB-parS participates in plasmid and chromosome segregation and condensation in predivisional bacterial cells. ParB polymerizes around the parS centromere(s) to form a higher-order assembly that serves to recruit cyto-skeletal ParA ATPases and SMC proteins for chromosome segregation. A hybrid model of the ParB-parS was built by combining and correlating computational models with experiment-derived information about size, shape, position of the symmetry axis within the shape, internal topology, DNA-protein interface, exposed surface patches, and prior knowledge. This first view of the ParB-parS leads us to propose how ParB spread on the chromosome to form a larger assembly.

Therapeutic potential of FtsZ inhibition: a patent perspective

INTRODUCTION

Filamentous temperature sensitive mutant Z (FtsZ), an essential protein for bacterial cell division, has emerged as an attractive therapeutic target for the development of efficacious antibacterial agents active against drug-sensitive and drug-resistant bacterial strains. Recently, FtsZ has garnered special attention in the antibacterial research field, which is evident by the amount of research papers and patents disclosed in the public domain. Because of the significance of FtsZ as a highly promising target for the development of novel antibacterial agents, it is timely to review the patents on this subject so far published to date.

AREAS COVERED

This review article covers the patent literature on FtsZ-targeting potential antibacterial agents up to November 2010, including their pharmacological findings.

EXPERT OPINION

Since FtsZ is well preserved in various bacteria, the FtsZ-targeting agents would act as novel broad-spectrum antibacterial drugs in addition to their use against particular bacteria, especially drug-resistant strains. Based on the increasing interest and advancement in this field of research, it looks almost certain that a good number of clinical candidates targeting FtsZ will emerge in the near future.

Multiple effects of benzamide antibiotics on FtsZ function

Cell division in almost all bacteria is orchestrated by the essential tubulin homologue FtsZ, which assembles into a ring-like structure and acts as a scaffold for the division machinery. Division was recently validated as an important target for antibiotics by the demonstration that low-molecular-weight inhibitors of FtsZ, called benzamides, can cure mice infected with Staphylococcus aureus. In treated cells of Bacillus subtilis we show that FtsZ assembles into foci throughout the cell, including abnormal locations at the cell poles and over the nucleoid. These foci are not inactive aggregates because they remain dynamic, turning over almost as rapidly as untreated polymers. Remarkably, although division is completely blocked, the foci efficiently recruit division proteins that normally co-assemble with FtsZ. However, they show no affinity for components of the Min or Nucleoid occlusion systems. In vitro, the benzamides strongly promote the polymerization of FtsZ, into hyperstable polymers, which are highly curved. Importantly, even at low concentrations, benzamides transform the structure of the Z ring, resulting in abnormal helical cell division events. We propose that benzamides act principally by promoting an FtsZ protomer conformation that is incompatible with a higher-order level of assembly needed to make a division ring.

Novel trisubstituted benzimidazoles, targeting Mtb FtsZ, as a new class of antitubercular agents

Libraries of novel trisubstituted benzimidazoles were created through rational drug design. A good number of these benzimidazoles exhibited promising MIC values in the range of 0.5-6 μg/mL (2-15 μM) for their antibacterial activity against Mtb H37Rv strain. Moreover, five of the lead compounds also exhibited excellent activity against clinical Mtb strains with different drug-resistance profiles. All lead compounds did not show appreciable cytotoxicity (IC(50) > 200 μM) against Vero cells, which inhibited Mtb FtsZ assembly in a dose dependent manner. The two lead compounds unexpectedly showed enhancement of the GTPase activity of Mtb FtsZ. The result strongly suggests that the increased GTPase activity destabilizes FtsZ assembly, leading to efficient inhibition of FtsZ polymerization and filament formation. The TEM and SEM analyses of Mtb FtsZ and Mtb cells, respectively, treated with a lead compound strongly suggest that lead benzimidazoles have a novel mechanism of action on the inhibition of Mtb FtsZ assembly and Z-ring formation.

Practical synthesis of PC190723, an inhibitor of the bacterial cell division protein FtsZ

A high-yielding and practical synthesis of the bacterial cell division inhibitor PC190723 is described. The synthesis is completed in a longest linear sequence of five steps from commercially available starting materials and can be readily executed on a multigram scale.

Insights into nucleotide recognition by cell division protein FtsZ from a mant-GTP competition assay and molecular dynamics

Essential cell division protein FtsZ forms the bacterial cytokinetic ring and is a target for new antibiotics. FtsZ monomers bind GTP and assemble into filaments. Hydrolysis to GDP at the association interface between monomers leads to filament disassembly. We have developed a homogeneous competition assay, employing the fluorescence anisotropy change of mant-GTP upon binding to nucleotide-free FtsZ, which detects compounds binding to the nucleotide site in FtsZ monomers and measures their affinities within the millimolar to 10 nM range. We have employed this method to determine the apparent contributions of the guanine, ribose, and the α-, β-, and γ-phosphates to the free energy change of nucleotide binding. Similar relative contributions have also been estimated through molecular dynamics and binding free energy calculations, employing the crystal structures of FtsZ-nucleotide complexes. We find an energetically dominant contribution of the β-phosphate, comparable to the whole guanosine moiety. GTP and GDP bind with similar observed affinity to FtsZ monomers. Loss of the regulatory γ-phosphate results in a predicted accommodation of GDP which has not been observed in the crystal structures. The binding affinities of a series of C8-substituted GTP analogues, known to inhibit FtsZ but not eukaryotic tubulin assembly, correlate with their inhibitory capacity on FtsZ polymerization. Our methods permit testing of FtsZ inhibitors targeting its nucleotide site, as well as compounds from virtual screening of large synthetic libraries. Our results give insight into the FtsZ-nucleotide interactions, which could be useful in the rational design of new inhibitors, especially GTP phosphate mimetics.

Synthesis of antimicrobial natural products targeting FtsZ: (+)-totarol and related totarane diterpenes

An efficient, convergent synthesis of totarol by a diastereoselective epoxide/alkene/arene bicyclization is described. The reported synthesis enables the preparation of related diterpenes totaradiol and totarolone as well as previously unavailable derivatives that exhibit comparable inhibition of the bacterial cell division protein FtsZ.

Creating an antibacterial with in vivo efficacy: synthesis and characterization of potent inhibitors of the bacterial cell division protein FtsZ with improved pharmaceutical properties

3-Methoxybenzamide (1) is a weak inhibitor of the essential bacterial cell division protein FtsZ. Alkyl derivatives of 1 are potent antistaphylococcal compounds with suboptimal drug-like properties. Exploration of the structure−activity relationships of analogues of these inhibitors led to the identification of potent antistaphylococcal compounds with improved pharmaceutical properties.

Calculations of binding affinity between C8-substituted GTP analogs and the bacterial cell-division protein FtsZ

The FtsZ protein is a self-polymerizing GTPase that plays a central role in bacterial cell division. Several C8-substituted GTP analogs are known to inhibit the polymerization of FtsZ by competing for the same binding site as its endogenous activating ligand GTP. Free energy calculations of the relative binding affinities to FtsZ for a set of five C8-substituted GTP analogs were performed. The calculated values agree well with the available experimental data, and the main contribution to the free energy differences is determined to be the conformational restriction of the ligands. The dihedral angle distributions around the glycosidic bond of these compounds in water are known to vary considerably depending on the physicochemical properties of the substituent at C8. However, within the FtsZ protein, this substitution has a negligible influence on the dihedral angle distributions, which fall within the narrow range of −140° to −90° for all investigated compounds. The corresponding ensemble average of the coupling constants ³J(C4,H1′) is calculated to be 2.95 ± 0.1 Hz. The contribution of the conformational selection of the GTP analogs upon binding was quantified from the corresponding populations. The obtained restraining free energy values follow the same trend as the relative binding affinities to FtsZ, indicating their dominant contribution.

Mapping flexibility and the assembly switch of cell division protein FtsZ by computational and mutational approaches

The molecular switch for nucleotide-regulated assembly and disassembly of the main prokaryotic cell division protein FtsZ is unknown despite the numerous crystal structures that are available. We have characterized the functional motions in FtsZ with a computational consensus of essential dynamics, structural comparisons, sequence conservation, and networks of co-evolving residues. Employing this information, we have constructed 17 mutants, which alter the FtsZ functional cycle at different stages, to modify FtsZ flexibility. The mutant phenotypes ranged from benign to total inactivation and included increased GTPase, reduced assembly, and stabilized assembly. Six mutations clustering at the long cleft between the C-terminal beta-sheet and core helix H7 deviated FtsZ assembly into curved filaments with inhibited GTPase, which still polymerize cooperatively. These mutations may perturb the predicted closure of the C-terminal domain onto H7 required for switching between curved and straight association modes and for GTPase activation. By mapping the FtsZ assembly switch, this work also gives insight into FtsZ druggability because the curved mutations delineate the putative binding site of the promising antibacterial FtsZ inhibitor PC190723.

FtsQ interaction mutants: a way to identify new antibacterial targets

FtsQ is a highly conserved component of the divisome that plays a central role in the assembly of early and late cell division proteins. The biological activity of this protein is still largely unknown, but its ability to interact with many components of the divisome was described by both two-hybrid assays and co-immunoprecipitation experiments. This paper describes the behaviour of ftsQ point mutants, created by random mutagenesis without regard to their phenotype, in which FtsQ is impaired in its ability to interact with its Escherichia coli division partners. Our results allow the identification of FtsQ residues involved in the interaction with other partner proteins and the determination of the biological significance of these interactions. The knowledge derived by this study could constitute not only the basis for understanding how these proteins assemble in the divisome, but also a starting point for the design of new antibacterial drugs that disrupt the bacterial division machinery.

The antibacterial cell division inhibitor PC190723 is an FtsZ polymer-stabilizing agent that induces filament assembly and condensation

Cell division protein FtsZ can form single-stranded filaments with a cooperative behavior by self-switching assembly. Subsequent condensation and bending of FtsZ filaments are important for the formation and constriction of the cytokinetic ring. PC190723 is an effective bactericidal cell division inhibitor that targets FtsZ in the pathogen Staphylococcus aureus and Bacillus subtilis and does not affect Escherichia coli cells, which apparently binds to a zone equivalent to the binding site of the antitumor drug taxol in tubulin (Haydon, D. J., Stokes, N. R., Ure, R., Galbraith, G., Bennett, J. M., Brown, D. R., Baker, P. J., Barynin, V. V., Rice, D. W., Sedelnikova, S. E., Heal, J. R., Sheridan, J. M., Aiwale, S. T., Chauhan, P. K., Srivastava, A., Taneja, A., Collins, I., Errington, J., and Czaplewski, L. G. (2008) Science 312, 1673-1675). We have found that the benzamide derivative PC190723 is an FtsZ polymer-stabilizing agent. PC190723 induced nucleated assembly of Bs-FtsZ into single-stranded coiled protofilaments and polymorphic condensates, including bundles, coils, and toroids, whose formation could be modulated with different solution conditions. Under conditions for reversible assembly of Bs-FtsZ, PC190723 binding reduced the GTPase activity and induced the formation of straight bundles and ribbons, which was also observed with Sa-FtsZ but not with nonsusceptible Ec-FtsZ. The fragment 2,6-difluoro-3-methoxybenzamide also induced Bs-FtsZ bundling. We propose that polymer stabilization by PC190723 suppresses in vivo FtsZ polymer dynamics and bacterial division. The biochemical action of PC190723 on FtsZ parallels that of the microtubule-stabilizing agent taxol on the eukaryotic structural homologue tubulin. Both taxol and PC190723 stabilize polymers against disassembly by preferential binding to each assembled protein. It is yet to be investigated whether both ligands target structurally related assembly switches.

Oleanolic acid and ursolic acid affect peptidoglycan metabolism in Listeria monocytogenes

The plant pentacyclic triterpenoids, oleanolic and ursolic acids, inhibit the growth and survival of many bacteria, particularly Gram-positive species, including pathogenic ones. The effect of these compounds on the facultative human pathogen Listeria monocytogenes was examined. Both acids affected cell morphology and enhanced autolysis of the bacterial cells. Autolysis of isolated cell walls was inhibited by oleanolic acid, but the inhibitory activity of ursolic acid was less pronounced. Both compounds inhibited peptidoglycan turnover and quantitatively affected the profile of muropeptides obtained after digestion of peptidoglycan with mutanolysin. These results suggest that peptidoglycan metabolism is a cellular target of oleanolic and ursolic acids.

An oldie but a goodie - cell wall biosynthesis as antibiotic target pathway

Bacterial cell wall biosynthesis represents the target pathway for penicillin, the first antibiotic that was clinically applied on a large scale. Penicillin, by means of its beta-lactam ring, inhibits a number of enzymes which participate in inserting monomeric cell wall building blocks into the cell wall polymer and which have been termed penicillin-binding proteins (PBPs). Ever since the introduction of penicillin, hundreds of beta-lactam antibiotics have been developed and details of their molecular activities elaborated. Meanwhile, various additional classes of antibiotics have been described, which inhibit the same pathway, yet use target molecules others than the PBPs. Such classes include the glycopeptide antibiotics, lipopeptide and lipodepsipeptide antibiotics, the lantibiotics and various other natural product antibiotics with comparatively complex structures. They usually target the membrane-bound steps of the biosynthesis pathway and the highly conserved lipid-bound intermediates of the building block such as lipid II, which represents a particular "Achilles' heel" for antibiotic attack. With in-depth analysis of the activity of more recently identified inhibitors and with the availability of novel techniques for studying prokaryotic cell biology, new insights were obtained into the molecular organisation of the cell wall biosynthesis machinery and its interconnections with other vital cellular processes such as cell division. This, in turn, provides hints for new targets to be exploited and for the development of novel cell wall biosynthesis inhibitors.

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.

Structure-activity relationship of isoform selective inhibitors of Rac1/1b GTPase nucleotide binding

The synthesis of a series of berberine, phenantridine and isoquinoline derivatives was realized to explore their Rho GTPase nucleotide inhibitory activity. The compounds were evaluated in a nucleotide binding competition assay against Rac1, Rac1b, Cdc42 and in a cellular Rac GTPase activation assay. The insertion of 19 AA in the splice variant Rac1b is shown to be sufficient to introduce a conformational difference that allows compounds 4, 21, 22, and 26 to exhibit selective inhibition of Rac 1b over Rac1.

Chemical tethering of motile bacteria to silicon surfaces

We chemically immobilized live, motile Escherichia coli on micrometer-scale, photocatalytically patterned silicon surfaces via amine- and carboxylic acid-based chemistries. Immobilization facilitated (i) controlled positioning; (ii) high resolution cell wall imaging via atomic force microscopy (AFM); and (iii) chemical analysis with time-of-flight-secondary ion mass spectrometry (ToF-SIMS). Spinning motion of tethered bacteria, captured with fast-acquisition video, proved microbe viability. We expect our protocols to open new experimental doors for basic and applied studies of microorganisms, from host-pathogen relationships, to microbial forensics and drug discovery, to biosensors and biofuel cell optimization.

Mitogen-activated protein (MAP) kinase/MAP kinase phosphatase regulation: roles in cell growth, death, and cancer

Mitogen-activated protein kinase dual-specificity phosphatase-1 (also called MKP-1, DUSP1, ERP, CL100, HVH1, PTPN10, and 3CH134) is a member of the threonine-tyrosine dual-specificity phosphatases, one of more than 100 protein tyrosine phosphatases. It was first identified approximately 20 years ago, and since that time extensive investigations into both mkp-1 mRNA and protein regulation and function in different cells, tissues, and organs have been conducted. However, no general review on the topic of MKP-1 exists. As the subject matter pertaining to MKP-1 encompasses many branches of the biomedical field, we focus on the role of this protein in cancer development and progression, highlighting the potential role of the mitogen-activated protein kinase (MAPK) family. Section II of this article elucidates the MAPK family cross-talk. Section III reviews the structure of the mkp-1 encoding gene, and the known mechanisms regulating the expression and activity of the protein. Section IV is an overview of the MAPK-specific dual-specificity phosphatases and their role in cancer. In sections V and VI, mkp-1 mRNA and protein are examined in relation to cancer biology, therapeutics, and clinical studies, including a discussion of the potential role of the MAPK family. We conclude by proposing an integrated scheme for MKP-1 and MAPK in cancer.

Antibacterial alkoxybenzamide inhibitors of the essential bacterial cell division protein FtsZ

3-Methoxybenzamide is a weak inhibitor of the essential bacterial cell division protein FtsZ. Exploration of the structure-activity relationships of 3-methoxybenzamide analogues led to the identification of potent anti-staphylococcal compounds.

Targeting the bacterial Z-ring

FtsZ is a prokaryotic homolog of eukaryotic tubulin and forms the essential bacterial cell division ring (Z-ring). A new study in this issue of Chemistry & Biology, Läppchen et al., provides further evidence that differences in nucleotide-binding properties of FtsZ and tubulin can be exploited to specifically target the bacterial Z-ring.

Probing FtsZ and tubulin with C8-substituted GTP analogs reveals differences in their nucleotide binding sites

The cytoskeletal proteins, FtsZ and tubulin, play a pivotal role in prokaryotic cell division and eukaryotic chromosome segregation, respectively. Selective inhibitors of the GTP-dependent polymerization of FtsZ could constitute a new class of antibiotics, while several inhibitors of tubulin are widely used in antiproliferative therapy. In this work, we set out to identify selective inhibitors of FtsZ based on the structure of its natural ligand, GTP. We found that GTP analogs with small hydrophobic substituents at C8 of the nucleobase efficiently inhibit FtsZ polymerization, whereas they have an opposite effect on the polymerization of tubulin. The inhibitory activity of the GTP analogs on FtsZ polymerization allowed us to crystallize FtsZ in complex with C8-morpholino-GTP, revealing the binding mode of a GTP derivative containing a nonmodified triphosphate chain.

Cell-division inhibitors: new insights for future antibiotics

The growing problem of antibiotic resistance has been exacerbated by the use of new drugs that are merely variants of older overused antibiotics. While it is naive to expect to restrain the spread of resistance without controlling antibacterial usage, the desperate need for drugs with novel targets has been recognized by health organizations, industry and academia alike. The wealth of knowledge available about the bacterial cell-division pathway has aided target-driven approaches to identify novel inhibitors. Here, we discuss the therapeutic potential of inhibiting bacterial cell division, and review the progress made in this exciting new area of antibacterial discovery.

The interactions of cell division protein FtsZ with guanine nucleotides

Prokaryotic cell division protein FtsZ, an assembling GTPase, directs the formation of the septosome between daughter cells. FtsZ is an attractive target for the development of new antibiotics. Assembly dynamics of FtsZ is regulated by the binding, hydrolysis, and exchange of GTP. We have determined the energetics of nucleotide binding to model apoFtsZ from Methanococcus jannaschii and studied the kinetics of 2'/3'-O-(N-methylanthraniloyl) (mant)-nucleotide binding and dissociation from FtsZ polymers, employing calorimetric, fluorescence, and stopped-flow methods. FtsZ binds GTP and GDP with K(b) values ranging from 20 to 300 microm(-1) under various conditions. GTP.Mg(2+) and GDP.Mg(2+) bind with slightly reduced affinity. Bound GTP and the coordinated Mg(2+) ion play a minor structural role in FtsZ monomers, but Mg(2+)-assisted GTP hydrolysis triggers polymer disassembly. Mant-GTP binds and dissociates quickly from FtsZ monomers, with approximately 10-fold lower affinity than GTP. Mant-GTP displacement measured by fluorescence anisotropy provides a method to test the binding of any competing molecules to the FtsZ nucleotide site. Mant-GTP is very slowly hydrolyzed and remains exchangeable in FtsZ polymers, but it becomes kinetically stabilized, with a 30-fold slower k(+) and approximately 500-fold slower k(-) than in monomers. The mant-GTP dissociation rate from FtsZ polymers is comparable with the GTP hydrolysis turnover and with the reported subunit turnover in Escherichia coli FtsZ polymers. Although FtsZ polymers can exchange nucleotide, unlike its eukaryotic structural homologue tubulin, GDP dissociation may be slow enough for polymer disassembly to take place first, resulting in FtsZ polymers cycling with GTP hydrolysis similarly to microtubules.

N-Benzyl-3-sulfonamidopyrrolidines as novel inhibitors of cell division in E. coli

A new small molecule inhibitor of bacterial cell division has been discovered using a high-throughput screen in Escherichia coli. Although the lead screening hit (534F6) exhibited modest inhibition of the GTPase activity of FtsZ (20+/-5% at 100microM of compound), a primary target for bacterial cell division inhibitors, several analogs caused potent bacterial growth inhibition with negligible antagonism of FtsZ GTPase activity. A library of analogs has been prepared and several alkyne-tagged photoaffinity probes have been synthesized for use in experiments to elucidate the primary target of this compound.

A Novel indole compound that inhibits Pseudomonas aeruginosa growth by targeting MreB is a substrate for MexAB-OprM

Drug efflux systems contribute to the intrinsic resistance of Pseudomonas aeruginosa to many antibiotics and biocides and hamper research focused on the discovery and development of new antimicrobial agents targeted against this important opportunistic pathogen. Using a P. aeruginosa PAO1 derivative bearing deletions of opmH, encoding an outer membrane channel for efflux substrates, and four efflux pumps belonging to the resistance nodulation/cell division class including mexAB-oprM, we identified a small-molecule indole-class compound (CBR-4830) that is inhibitory to growth of this efflux-compromised strain. Genetic studies established MexAB-OprM as the principal pump for CBR-4830 and revealed MreB, a prokaryotic actin homolog, as the proximal cellular target of CBR-4830. Additional studies establish MreB as an essential protein in P. aeruginosa, and efflux-compromised strains treated with CBR-4830 transition to coccoid shape, consistent with MreB inhibition or depletion. Resistance genetics further suggest that CBR-4830 interacts with the putative ATP-binding pocket in MreB and demonstrate significant cross-resistance with A22, a structurally unrelated compound that has been shown to promote rapid dispersion of MreB filaments in vivo. Interestingly, however, ATP-dependent polymerization of purified recombinant P. aeruginosa MreB is blocked in vitro in a dose-dependent manner by CBR-4830 but not by A22. Neither compound exhibits significant inhibitory activity against mutant forms of MreB protein that bear mutations identified in CBR-4830-resistant strains. Finally, employing the strains and reagents prepared and characterized during the course of these studies, we have begun to investigate the ability of analogues of CBR-4830 to inhibit the growth of both efflux-proficient and efflux-compromised P. aeruginosa through specific inhibition of MreB function.

Inhibition of bacterial cell division protein FtsZ by cinnamaldehyde

Cinnamaldehyde is a natural product from spices that inhibits cell separation in Bacillus cereus. Cell division is regulated by FtsZ, a prokaryotic homolog of tubulin. FtsZ assembles into the Z-ring at the site of cell division. Here, we report the effect of cinnamaldehyde on FtsZ and hence on the cell division apparatus. Cinnamaldehyde decreases the in vitro assembly reaction and bundling of FtsZ. It is found that cinnamaldehyde perturbs the Z-ring morphology in vivo and reduces the frequency of the Z ring per unit cell length of Escherichia coli. In addition, GTP dependent FtsZ polymerization is inhibited by cinnamaldehyde. Cinnamaldehyde inhibits the rate of GTP hydrolysis and binds FtsZ with an affinity constant of 1.0+/-0.2 microM(-1). Isothermal titration calorimetry reveals that binding of cinnamaldehyde to FtsZ is driven by favorable enthalpic interactions. Further, we map the cinnamaldehyde binding region of FtsZ, using the saturation transfer difference-nuclear magnetic resonance and an in silico docking model. Both predict the cinnamaldehyde binding pocket at the C terminal region involving the T7 loop of FtsZ. Our results show that cinnamaldehyde binds FtsZ, perturbs the cytokinetic Z-ring formation and inhibits its assembly dynamics. This suggests that cinnamaldehyde, a small molecule of plant origin, is a potential lead compound that can be developed as an anti-FtsZ agent towards drug design.

Synthesis of Kaempferitrin

A short synthesis of Kaempferitrin (1), a 3,7-diglycosylflavone, is reported. Key features include the synthesis of a protected form of kaempferol in which all four hydroxy groups are differentiated and the first bis-glycosylation of a dihydroxyflavone. This synthesis will allow the preparation of derivatives for further explorations into the origins of this compound's biological activity.

Of the morphogenes that make a ring, a rod and a sphere in Escherichia coli

In 1993, William Donachie wrote "The success of molecular genetics in the study of bacterial cell division has been so great that we find ourselves, armed with much greater knowledge of detail, confronted once again with the same naive questions that we set to answer in the first place". Indeed, attempts to answer the apparently simple question of how a bacterial cell divides have led to a wealth of new knowledge, in particular over the past decade and a half. And while some questions have been answered to a great extent since the early reports of isolation of division mutants of Escherichia coli, some key pieces of the puzzle remain elusive. In addition to it being a fundamental process in bacteria that merits investigation in its own right, studying the process of cell division offers an abundance of new targets for the development of new antibacterial compounds that act directly against key division proteins and other components of the cytoskeleton, which are encoded by the morphogenes of E. coli. This review aims to present the reader with a snapshot summary of the key players in E. coli morphogenesis with emphasis on cell division and the rod to sphere transition.