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

This variant is of interest because it maintains cellular phenotypes despite an increase of the CTT κ by a factor of two when compared to the WT CTT. Like WT, we observed a canonical dependence of light scattering intensity on monovalent salt ( Figure 4D ). At high salt, the interactions that hold the bundles together are screened and CTLV4 forms unbundled polymers that are similar to those formed by WT FtsZ (Figure 4E ). Simulations predict the CTT of CTLV4 is 10% smaller than the WT CTT ( Figure 2C ). Compaction is mediated by increased electrostatic interactions between charged blocks on the CTT sequence. While the simulations illustrate charge-dependent intramolecular interactions, these interactions could also occur in an intermolecular fashion. Concordant with this expectation, we observed a two-fold increase in the peak scattering intensity in the presence of 50 mM KCl for the CTLV4 variant when compared to the WT FtsZ ( Figure 4F ). This increase in scattering intensity derives from two distinct features as revealed by negative stain EM images ( Figure 4E) . When compared to the WT FtsZ, CTLV4 forms longer polymers that become part of thicker bundles in the presence of low salt. Figure 4F shows a comparison of the relative strengths of filament / polymer bundling by comparing the maximum scattering intensities measured for the WT versus CTLV4 in the presence of three different concentrations of KCl. The major differences between the variants are manifest at low salt. However, under physiologically relevant salt concentrations, the morphological differences All rights reserved. No reuse allowed without permission.