The Cell Division Protein FtsZ from Streptococcus pneumoniae Exhibits a GTPase Activity Delay

The cell division protein FtsZ assembles in vitro by a mechanism of cooperative association dependent on GTP, monovalent cations, and Mg2+. We have analyzed the GTPase activity and assembly dynamics of Streptococcus pneumoniae FtsZ (SpnFtsZ). SpnFtsZ assembled in an apparently cooperative process, with a higher critical concentration than values reported for other FtsZ proteins. It sedimented in the presence of GTP as a high molecular mass polymer with a well defined size and tended to form double-stranded filaments in electron microscope preparations. GTPase activity depended on K+ and Mg2+ and was inhibited by Na+. GTP hydrolysis exhibited a delay that included a lag phase followed by a GTP hydrolysis activation step, until reaction reached the GTPase rate. The lag phase was not found in polymer assembly, suggesting a transition from an initial non-GTP-hydrolyzing polymer that switches to a GTP-hydrolyzing polymer, supporting models that explain FtsZ polymer cooperativity. Background: The FtsZ cell division protein has nucleotide-dependent GTPase and assembly activities. The mechanism coupling these two activities is uncertain. Results: Purified Streptococcus pneumoniae FtsZ (SpnFtsZ) presents a lag in the GTPase activity but not in filament assembly. Conclusion: The differences between the initial polymerization and GTPase activities of SpnFtsZ suggest a transition from inactive to active polymers. Significance: Nucleotide hydrolysis by SpnFtsZ polymers involves an activation step.