Polymerization of C-terminally truncated Mycobacterium tuberculosis FtsZ is unlikely to be physiologically relevant

Mycobacterium tuberculosis FtsZ (MtbFtsZ) exhibits unusually slow polymerization kinetics in vitro (White et al., 2000). Recently, Anand et al. (2004) hypothesized that removal of the non-conserved C terminus would bestow rapid polymerization to MtbFtsZ, comparable to the much faster-polymerizing Escherichia coli FtsZ (EcFtsZ) (Mukherjee & Lutkenhaus, 1999). Indeed, MtbFtsZ(ΔC169), in which the last 169 residues were deleted (Δ211379; Fig. 1), was found to polymerize much faster than wild-type MtbFtsZ (Anand et al., 2004). It also formed polymers that were 1·5-times thicker and that exhibited an altered morphology, compared with wild-type MtbFtsZ protofilaments (White et al., 2000). We show here, however, that the three-dimensional structure of MtbFtsZ(ΔC169) is so perturbed the truncation exposes a large hydrophobic patch that is normally buried (Fig. 2) that polymerization of MtbFtsZ(ΔC169) is unlikely to be physiologically relevant. The cause(s) of the slow polymerization of wild-type MtbFtsZ must therefore be sought elsewhere.