Evolved sequence features within the intrinsically disordered tail influence FtsZ assembly and bacterial cell division

Megan C. Cohan; Ammon E. Posey; Steven J. Grigsby; Anuradha Mittal; Alex S. Holehouse; Paul J. Buske; Petra A. Levin; Rohit V. Pappu

To further assess the robustness of altering charge patterning within evolutionarily observed bounds (Figure 1D) , we quantified the comparative efficiencies of GTP hydrolysis of FtsZ variants. Figure 4G shows results from measurements that compare the efficiencies of WT FtsZ to those for CTLV4 and ∆CTT. The latter is a variant of FtsZ that lacks the CTT. The efficiency of GTP hydrolysis remains unchanged for CTLV4 when compared to the WT FtsZ ( Figure 4G ). Higher-order assembly, such as protofilament bundling and Z-ring formation, are compromised for ∆CTT (Buske and Levin, 2013; Sundararajan and Goley, 2017; Sundararajan et al., 2015) and we do not observe a measurable increase in light scattering that is distinguishable from the background. Despite this, we find that ∆CTT is much more efficient as a GTPase with an enzymatic activity that is ~3 times higher than the WT or CTLV4. Taken together with the observation that GTP hydrolysis promotes the severing of protofilaments (Mukherjee and Lutkenhaus, 1998) our data suggest that ∆CTT, as a result of being unencumbered by the absence of the CTT, is able to bind GTP, polymerize, hydrolyze GTP, disassemble and repeat the cycle in an extremely efficient manner. Accordingly, we propose that the CTT, which is essential for Z-ring formation, promotes FtsZ assembly and this suppresses GTPase activity. This suppression could arise from steric effects of the CTT, a reduction in subunit turnover, and possible protofilament stabilization through interactions with neighboring filaments mediated by the CTT.