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To understand the polymerization dynamics of FtsZ, a bacterial cell division protein similar to tubulin, insight is required into the nature of the nucleotide bound to the polymerized protein. In a previous study, we showed that the FtsZ polymers contain mostly GDP. A recent study challenged this result, suggesting that the polymerized FtsZ is in a GTP-bound state. Here, we show that, when radiolabelled [gamma-32P]-GTP is used to polymerize FtsZ, GTP is hydrolysed instantaneously. The FtsZ polymer contains both GDP and the radiolabelled inorganic phosphate.

Bacteria and archaea usually divide symmetrically by formation of a septum in the middle of the cell. A key event in cell division is the assembly of the FtsZ ring. FtsZ is the prokaryotic homolog of tubulin and forms polymers in the presence of guanine nucleotides. Here, we specifically address the polymerization of FtsZ and the role of nucleotide hydrolysis in polymer formation and stabilization. Recent structural and biochemical results are discussed and a model for FtsZ polymerization, similar to that for tubulin, is presented.

The prokaryotic tubulin homologue FtsZ polymerizes in vitro in a nucleotide dependent fashion. Here we report that replacement of the strictly conserved Asp212 residue of Escherichia coli FtsZ by a Cys or Asn, but not by a Glu residue results in FtsZ that polymerizes with divalent cations in the absence of added GTP. FtsZ D212C and D212N mutants co-purify with GTP as bound nucleotide, providing an explanation for the unusual phenotype. We conclude that D212 plays a critical role in the coordination of a metal ion and the nucleotide at the interface of two FtsZ monomers.