Bacterial FtsZ monomers are ~ 300-400 amino acid proteins that contain one molecule each of GTP/GDP nucleotides, Mg ++ and K + as cofactors. FtsZ filaments are formed by adding non-covalent top-to-bottom adjacent monomers (Figure ). FtsZ filaments are dynamic assembling / disassembling protein polymers constantly exchanging with soluble monomers every ~10 seconds . According to crystallographic, mutational and other studies 2, 3 , FtsZ contains two main binding-cavities for known ligands, the interdomain cleft (idc) and the nucleotide binding domain (nbd). The nbd binds GTP/GDP, and participates in FtsZ folding and GTP γ-phosphate hydrolysis . FtsZ switches from a closed-relaxed conformation in monomers to an open-tense conformation in filaments . Suggested by crystallographic observations , the FtsZ transitions were confirmed by several studies 3, 7-9 . At each dimerization step, a new interface is generated including the cocatalytic loop from one of the monomers and the complementary GTP-containing nbd from other monomer.