Differential assembly properties of Escherichia coli FtsZ and Mycobacterium tuberculosis FtsZ: an analysis using divalent calcium.

The assembly of FtsZ is considered to be a fundamental process during the bacterial cytokinesis. We used several complimentary techniques to probe the assembly of recombinant Escherichia coli FtsZ (EcFtsZ) and Mycobacterium tuberculosis FtsZ (MtbFtsZ) proteins in vitro. As documented earlier, EcFtsZ was found to polymerize at much faster rate than MtbFtsZ. Interestingly, we found that MtbFtsZ produced higher sedimentable polymerized mass than that of the EcFtsZ and that MtbFtsZ formed thicker protofilaments than that of the EcFtsZ. The results indicated that the EcFtsZ polymers are more labile than the MtbFtsZ polymers. Further, divalent calcium exerted strikingly different effects on the assembly of EcFtsZ and MtbFtsZ. Divalent calcium strongly enhanced the assembly of EcFtsZ and promoted bundling and stability of the protofilaments. In contrast, it had no detectable effect on the assembly of MtbFtsZ. In vitro, divalent calcium bound to EcFtsZ with much stronger affinity than to MtbFtsZ and significantly affected the secondary structure of EcFtsZ whereas it did not cause any detectable change in the secondary structure of MtbFtsZ. The results suggested that the assembly characteristics of EcFtsZ and MtbFtsZ are different and indicated that the assembly dynamics of these proteins are regulated by different mechanisms.