Functional characterization of the cell division inhibitor MipZ

ended

Correct positioning of the division plane is essential for the generation of normal offspring. In Caulobacter crescentus, the spatiotemporal control of cell division is mediated by MipZ, a conserved P-loop ATPase forming bipolar gradients with a concentration minimum at the cell centre. Antagonizing the polymerization of the essential divisome component FtsZ, MipZ inhibits divisome assembly near the poles, thereby limiting cytokinesis to midcell. Gradient formation involves a dynamic localization cycle, in which freely diffusible MipZ monomers interact with polar complexes of the centromere-binding protein ParB and then dimerize in an ATP-dependent manner. Dimers dissociate from ParB and are immobilized within the cell through non-specific interaction with chromosomal DNA. Spontaneous ATP hydrolysis triggers disassembly of the complex, releasing MipZ monomers that are recaptured by ParB. How ParB stimulates dimer formation and how DNA-bound dimers inhibit FtsZ assembly is still unknown. We will address these questions by characterizing previously isolated MipZ mutants with FtsZ/ParB interaction defects, using a combination of fluorescence microscopy, two-hybrid analysis, biochemistry, and biophysical techniques such as surface plasmon resonance, microscale thermophoresis or hydrogen-deuterium-exchange mass spectrometry. We will also use synthetic biological and modelling approaches to rebuild the system in a simplistic form to thus gain in-depth knowledge of the function of the different elements.