Bacteriophage Tubulins: Carrying Their Own Cytoskeleton Key

SummaryCytoskeletal elements are well known to be widespread in eukaryotes and prokaryotes, providing important, diverse functions for cells large and small. Two new studies report that some bacteriophages encode their own tubulin homologs to facilitate phage reproduction within the host cell

Phase chaos in the anisotropic complex Ginzburg-Landau Equation

Of the various interesting solutions found in the two-dimensional complex Ginzburg-Landau equation for anisotropic systems, the phase-chaotic states show particularly novel features. They exist in a broader parameter range than in the isotropic case, and often even broader than in one dimension. They typically represent the global attractor of the system. There exist two variants of phase chaos: a quasi-one dimensional and a two-dimensional solution. The transition to defect chaos is of intermittent type.Comment: 4 pages RevTeX, 5 figures, little changes in figures and references, typos removed, accepted as Rapid Commun. in Phys. Rev.

Proteolysis-Dependent Remodeling of the Tubulin Homolog FtsZ at the Division Septum in \u3ci\u3eEscherichia coli\u3c/i\u3e

During bacterial cell division a dynamic protein structure called the Z-ring assembles at the septum. The major protein in the Z-ring in Escherichia coli is FtsZ, a tubulin homolog that polymerizes with GTP. FtsZ is degraded by the two-component ATP-dependent protease ClpXP. Two regions of FtsZ, located outside of the polymerization domain in the unstructured linker and at the C-terminus, are important for specific recognition and degradation by ClpXP. We engineered a synthetic substrate containing green fluorescent protein (Gfp) fused to an extended FtsZ C-terminal tail (residues 317–383), including the unstructured linker and the C-terminal conserved region, but not the polymerization domain, and showed that it is sufficient to target a non-native substrate for degradation in vitro. To determine if FtsZ degradation regulates Z-ring assembly during division, we expressed a full length Gfp-FtsZ fusion protein in wild type and clp deficient strains and monitored fluorescent Z-rings. In cells deleted for clpX or clpP, or cells expressing protease-defective mutant protein ClpP(S97A), Z-rings appear normal; however, after photobleaching a region of the Z-ring, fluorescence recovers ~70% more slowly in cells without functional ClpXP than in wild type cells. Gfp-FtsZ(R379E), which is defective for degradation by ClpXP, also assembles into Z-rings that recover fluorescence ~2-fold more slowly than Z-rings containing Gfp-FtsZ. In vitro, ClpXP cooperatively degrades and disassembles FtsZ polymers. These results demonstrate that ClpXP is a regulator of Z-ring dynamics and that the regulation is proteolysis-dependent. Our results further show that FtsZ-interacting proteins in E. coli fine-tune Z-ring dynamics

The Division Inhibitor EzrA Contains a Seven-Residue Patch Required for Maintaining the Dynamic Nature of the Medial FtsZ Ring▿

The essential cytoskeletal protein FtsZ assembles into a ring-like structure at the nascent division site and serves as a scaffold for the assembly of the prokaryotic division machinery. We previously characterized EzrA as an inhibitor of FtsZ assembly in Bacillus subtilis. EzrA interacts directly with FtsZ to prevent aberrant FtsZ assembly and cytokinesis at cell poles. EzrA also concentrates at the cytokinetic ring in an FtsZ-dependent manner, although its precise role at this position is not known. Here, we identified a conserved patch of amino acids in the EzrA C terminus that is essential for localization to the FtsZ ring. Mutations in this patch (designated the “QNR patch”) abolish EzrA localization to midcell but do not significantly affect EzrA's ability to inhibit FtsZ assembly at cell poles. ezrA QNR patch mutant cells exhibit stabilized FtsZ assembly at midcell and are significantly longer than wild-type cells, despite lacking extra FtsZ rings. These results indicate that EzrA has two distinct activities in vivo: (i) preventing aberrant FtsZ ring formation at cell poles through inhibition of de novo FtsZ assembly and (ii) maintaining proper FtsZ assembly dynamics within the medial FtsZ ring, thereby rendering it sensitive to the factors responsible for coordinating cell growth and cell division

ClpX Inhibits FtsZ Assembly in a Manner That Does Not Require Its ATP Hydrolysis-Dependent Chaperone Activity▿ †

ClpX is a well-characterized bacterial chaperone that plays a role in many processes, including protein turnover and the remodeling of macromolecular complexes. All of these activities require ATP hydrolysis-dependent, ClpX-mediated protein unfolding. Here we used site-directed mutagenesis in combination with genetics and biochemistry to establish that ClpX inhibits assembly of the conserved division protein FtsZ through a noncanonical mechanism independent of its role as an ATP-dependent chaperone