Imaging-Based Identification of a Critical Regulator of FtsZ Protofilament Curvature in Caulobacter

Abstract

SUMMARY FtsZ is an essential bacterial GTPase that polymerizes at midcell, recruits the division machinery, and may generate constrictive forces necessary for cytokinesis. However, many of the mechanistic details underlying these functions are unknown. We sought to identify FtsZ-binding proteins that influence FtsZ function in Caulobacter crescentus. Here, we present a microscopy-based screen through which we discovered two FtsZ-binding proteins, FzlA and FzlC. FzlA is conserved in α-proteobacteria and was found to be functionally critical for cell division in Caulobacter. FzlA altered FtsZ structure both in vivo and in vitro, forming stable higher order structures that were resistant to depolymerization by MipZ, a spatial determinant of FtsZ assembly. Electron microscopy revealed that FzlA organizes FtsZ protofilaments into striking helical bundles. The degree of curvature induced by FzlA depended on the nucleotide bound to FtsZ. Induction of FtsZ curvature by FzlA carries implications for regulating FtsZ function by modulating its superstructure.

Extreme C Terminus of Bacterial Cytoskeletal Protein FtsZ Plays Fundamental Role in Assembly Independent of Modulatory Proteins

“…B. subtilis and Mycobacterium tuberculosis) (42,56) bundle to a significantly greater degree than others (e.g. E. coli and C. crescentus) (3,57). It will be exciting to determine the impact of the CTV from various species of FtsZ on assembly.…”

The bacterial divisome: ready for its close-up

“…As a result, we learned that many diverse bacteria, euryarchaea, plant plastids and even a few primitive mitochondria harbour Z rings, and that perturbing localization of the rings results in cytokinesis defects. Moreover, fluorescence microscopy has been crucial in screening for Z ring binding proteins [20][21][22][23], particularly as many of these proteins would be very hard to identify by genetic or biochemical methods because of transient interactions and/or modest phenotypes when inactivated.…”

Developmental and environmental regulatory pathways in alpha-proteobacteria

“…While our knowledge of the spatial and temporally regulated mechanisms underlying Z-ring formation had been scarce in the past, tremendous progress has been made in the last five years in elucidating the fundamental processes of cell division. The identification of new players controlling cytokinesis in C. crescentus -particularly MipZ, DipM, KidO and FzlA -is unearthing the mechanisms that (alpha-proteo)bacteria use for the proper timing and positioning of the cytokinetic machinery (63,(83)(84)(85). Importantly, recent work has also illuminated how chromosome segregation occurs in C. crescentus, and how this process plays a central role in division control.…”

“…A microscopy-based localization screen to search for FtsZ-interacting proteins unearthed FzlA (and FzlC) as unknown regulator(s) of FtsZ (85). FzlA is a glutathione Stransferase (GST) family member, but binding to glutathione was not observed in vitro, suggesting that FzlA function does not involve glutathione.…”

“…FzlA is a glutathione Stransferase (GST) family member, but binding to glutathione was not observed in vitro, suggesting that FzlA function does not involve glutathione. FzlC is a hypothetical protein with limited homology to known heparinases (85). Both FzlA and FzlC are widely conserved in alpha-proteobacteria.…”