Superresolution Investigation of the E. coli Cell Division Ring during Constriction

Abstract

The E. coli cell division machinery are recruited to midcell by a ring-like structure formed by the highly conserved FtsZ protein. This “Z-ring” scaffold can generate a membrane bending force that may be critical for cytokinesis. Several mechanistic models for Z-ring force generation have been presented, but are limited in detail by insufficient data regarding the arrangement of FtsZ filaments within the Z-ring and regarding the role of FtsZ's GTPase activity in constriction progression. Structural details about the Z-ring have recently become clearer due to advancements in both optical and electron microscopy. Super-resolution fluorescence microscopy and electron cryotomography studies support a loosely bundled arrangement of FtsZ filaments, resulting in both sparse regions and dense clusters within the Z-ring. Super-resolution imaging also revealed that the Z-ring can adopt both a single-ring conformation at midcell and a multiple-ring conformation reminiscent of a tight helix. We have built upon these previous studies to determine the three-dimensional structure of the E. coli Z-ring in super resolution using Photoactivated Localization Microscopy (PALM) and analyze its changes during constriction. We used quantitative analyses of PALM and time-lapse data to assess the plausibility of various FtsZ-centric constriction mechanisms. We found that the cell wall constriction rate is not correlated to Z-ring assembly/disassembly dynamics, density, or GTPase activity. These characterizations help refine and re-define the role of FtsZ in cytokinesis.