The assembly and stability of FtsZ protofilaments have been shown to play critical roles in bacterial cytokinesis. Recent evidence suggests that FtsZ may be considered as an important antibacterial drug target. Curcumin, a dietary polyphenolic compound, has been shown to have a potent antibacterial activity against a number of pathogenic bacteria including Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus. We found that curcumin induced filamentation in the Bacillus subtilis 168, suggesting that it inhibits bacterial cytokinesis. Further, curcumin strongly inhibited the formation of the cytokinetic Z-ring in B. subtilis 168 without detectably affecting the segregation and organization of the nucleoids. Since the assembly dynamics of FtsZ protofilaments plays a major role in the formation and functioning of the Z-ring, we analysed the effects of curcumin on the assembly of FtsZ protofilaments. Curcumin inhibited the assembly of FtsZ protofilaments and also increased the GTPase activity of FtsZ. Electron microscopic analysis showed that curcumin reduced the bundling of FtsZ protofilaments in vitro. Further, curcumin was found to bind to FtsZ in vitro with a dissociation constant of 7.3+/-1.8 microM and the agent also perturbed the secondary structure of FtsZ. The results indicate that the perturbation of the GTPase activity of FtsZ assembly is lethal to bacteria and suggest that curcumin inhibits bacterial cell proliferation by inhibiting the assembly dynamics of FtsZ in the Z-ring.

Feedback-Driven Assembly of the Axon Initial Segment Highlights d Ankyrin-G in complex with EBs recruits microtubule bundles to the plasma membrane d TRIM46 is a rescue factor that forms stable parallel microtubule bundles d TRIM46-bound microtubules direct Neurofascin-186 trafficking to the proximal axon d Ankyrin-G controls Neurofascin-186 retention in the axon initial segment

Highlights d CLASP stabilizes damaged microtubule lattices d CLASP converts partial protofilament assemblies into complete tubes d CLASP promotes complete repair of microtubule lattice defects d CLASP inhibits softening of microtubules bent by hydrodynamic flow

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Abstractγ-tubulin ring complex (γ-TuRC) is the major microtubule-nucleating factor. After nucleation, microtubules can be released from γ-TuRC and stabilized by other proteins, such as CAMSAPs, but the biochemical cross-talk between minus-end regulation pathways is poorly understood. Here, we reconstituted this process in vitro using purified components. We found that all CAMSAP proteins could bind to the minus-ends of γ-TuRC-attached microtubules. CAMSAP2 and CAMSAP3, which decorate and stabilize growing minus ends, but not the minus-end tracking protein CAMSAP1 induced microtubule release from γ-TuRC. CDK5RAP2, a γ-TuRC-interactor, and CLASP2, a regulator of microtubule growth, stimulated γ-TuRC-dependent microtubule nucleation, but only CDK5RAP2 inhibited CAMSAP-driven microtubule detachment by suppressing CAMSAP binding to γ-TuRC-anchored minus ends. CDK5RAP2 also improved γ-TuRC selectivity for 13-rather than 14-protofilament microtubules in microtubule-capping assays. Our results support a model whereby CAMSAPs exploit an imperfect attachment between γ-TuRC and the nucleated microtubule to promote minus-end elongation and release, whereas CDK5RAP2 improves the fit between γ-TuRC and 13-protofilament microtubules and enhances nucleation.