Cooperative ordering of treadmilling filaments in cytoskeletal networks of FtsZ and its crosslinker ZapA

Paulo Caldas,Mar López-Pelegrín,Daniel J G Pearce,Nazmi Burak Budanur,Martin Loose,Jan Brugués

doi:10.1038/s41467-019-13702-4

Abstract

During bacterial cell division, the tubulin-homolog FtsZ forms a ring-like structure at the center of the cell. This Z-ring not only organizes the division machinery, but treadmilling of FtsZ filaments was also found to play a key role in distributing proteins at the division site. What regulates the architecture, dynamics and stability of the Z-ring is currently unknown, but FtsZ-associated proteins are known to play an important role. Here, using an in vitro reconstitution approach, we studied how the well-conserved protein ZapA affects FtsZ treadmilling and filament organization into large-scale patterns. Using high-resolution fluorescence microscopy and quantitative image analysis, we found that ZapA cooperatively increases the spatial order of the filament network, but binds only transiently to FtsZ filaments and has no effect on filament length and treadmilling velocity. Together, our data provides a model for how FtsZ-associated proteins can increase the precision and stability of the bacterial cell division machinery in a switch-like manner.

Highlights

During bacterial cell division, the tubulin-homolog FtsZ forms a ring-like structure at the center of the cell
With the help of novel image analysis tools, we quantified the influence of ZapA on FtsZ on three different spatial scales: First, we analyzed the large-scale organization of the membranebound filament network; we studied the underlying polymerization dynamics, and we quantified the behavior of single molecules
To study the effect of ZapA on the architecture and dynamics of the FtsZ filament network, we took advantage of an in vitro system based on supported lipid bilayers and purified proteins (Fig. 1a)

Summary

Introduction

The tubulin-homolog FtsZ forms a ring-like structure at the center of the cell. Mutants of Escherichia coli lacking one of the FtsZ-associated proteins ZapA, ZapB, ZapC or ZapD are usually longer than wild-type cells with a more heterogeneous cell length distribution They show mislocalized or misaligned Z-rings and skewed division septae, with their corresponding phenotype becoming even more severe in cells missing more than one Zap protein[8,9,10,11]. ZapA was found to reduce the GTPase activity of FtsZ suggesting that it can slow down FtsZ polymerization dynamics[15,16,17], even though this effect depends on buffer conditions[14,18] Together, these findings have led to a model where ZapA stabilizes the Z-ring by promoting antiparallel bundling of filaments and reducing polymer turnover[12,16]. Even though the reorganization of the network is slowed down significantly, ZapA leaves the treadmilling rate of FtsZ unchanged

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Conclusion