Architecture of the ring formed by the tubulin homologue FtsZ in bacterial cell division

Abstract

Membrane constriction is a prerequisite for cell division. The most common membrane constriction system in prokaryotes is based on the tubulin homologue FtsZ, whose filaments in E. coli are anchored to the membrane by FtsA and enable the formation of the Z-ring and divisome. The precise architecture of the FtsZ ring has remained enigmatic. In this study, we report three-dimensional arrangements of FtsZ and FtsA filaments in C. crescentus and E. coli cells and inside constricting liposomes by means of electron cryomicroscopy and cryotomography. In vivo and in vitro, the Z-ring is composed of a small, single-layered band of filaments parallel to the membrane, creating a continuous ring through lateral filament contacts. Visualisation of the in vitro reconstituted constrictions as well as a complete tracing of the helical paths of the filaments with a molecular model favour a mechanism of FtsZ-based membrane constriction that is likely to be accompanied by filament sliding.DOI: http://dx.doi.org/10.7554/eLife.04601.001

Defining the rate-limiting processes of bacterial cytokinesis

“…We note that, in vitro, membrane-attached FtsZ can form long, continuous protofilaments (33,35) and that a recent ECT study observed long, single-layered protofilaments at cell division sites (35). These studies support a smooth, continuous Z-ring organization.…”

“…Active GTP hydrolysis may thus serve to constantly remodel the Z-ring, generating a discontinuous, clustered organization that can reorganize promptly in response to cellular cues. This GTPase-dependent remodeling may explain why long FtsZ protofilaments were more apparent with an overexpressed FtsZ variant with low GTPase activity (D212A) (35).…”

“…For example, purified, membrane-tethered FtsZ was shown to assemble into ring-like structures that deform and constrict liposome membranes (30)(31)(32)(33)(34)(35). Mechanistically, it has been proposed that a constrictive force could be generated by the bending of FtsZ protofilaments because of their preferred curvature or GTP hydrolysis-induced conformation change (36)(37)(38)(39)(40)(41), immediate reannealing of FtsZ protofilaments upon GTP hydrolysis-induced subunit loss (42), condensation of FtsZ protofilaments caused by their lateral affinity (43), or a combination of these mechanisms (38,42,44,45).…”

The bacterial divisome: ready for its close-up

“…These experiments suggested that FtsZ and FtsA were sufficient to exert a significant inward pinching force on a membrane and could be doing so in the cell. Cryo-EM of inside-out Z ring complexes on liposomes displayed long parallel bundled filaments on the membrane [71,95], supporting the in vivo cryo-ET data. The second type of reconstitution comes from Martin Loose and Tim Mitchison, who investigated the interplay between purified FtsA and FtsZ on supported lipid bilayers (SLBs) [96].…”

“…Such an arrangement is consistent with known interactions between FtsZ and its membrane anchor proteins such as FtsA (ZipA is absent in C. crescentus), which are lower in abundance than FtsZ and should periodically tether FtsZ polymers to the membrane. A more recent cryo-ET study also visualized long polymers, and more controls were done that suggested these polymers were FtsZ itself [71]. A major conclusion of this study was that the Z ring is comprised at least partially of continuous long FtsZ polymers, which seems to be at odds with the patchy nature of Z rings visualized by 3D-SIM and PALM.…”