E93R substitution of Escherichia coli FtsZ induces bundling of protofilaments, reduces GTPase activity, and impairs bacterial cytokinesis.

Recently, we found that divalent calcium has no detectable effect on the assembly of Mycobacterium tuberculosis FtsZ (MtbFtsZ), whereas it strongly promoted the assembly of Escherichia coli FtsZ (EcFtsZ). While looking for potential calcium binding residues in EcFtsZ, we found a mutation (E93R) that strongly promoted the assembly of EcFtsZ. The mutation increased the stability and bundling of the FtsZ protofilaments and produced a dominating effect on the assembly of the wild type FtsZ (WT-FtsZ). Although E93R-FtsZ was found to bind to GTP similarly to the WT-FtsZ, it displayed lower GTPase activity than the WT-FtsZ. E93R-FtsZ complemented for its wild type counterpart as observed by a complementation test using JKD7-1/pKD3 cells. However, the bacterial cells became elongated upon overexpression of the mutant allele. We modeled the structure of E93R-FtsZ using the structures of MtbFtsZ/Methanococcus jannaschi FtsZ (MjFtsZ) dimers as templates. The MtbFtsZ-based structure suggests that the Arg(93)-Glu(138) salt bridge provides the additional stability, whereas the effect of mutation appears to be indirect (allosteric) if the EcFtsZ dimer is similar to that of MjFtsZ. The data presented in this study suggest that an increase in the stability of the FtsZ protofilaments is detrimental for the bacterial cytokinesis.