Escherichia coli ZipA Organizes FtsZ Polymers into Dynamic Ring-Like Protofilament Structures.

Marcin Krupka,Mercedes Jiménez,Marta Sobrinos-Sanguino,Germán Rivas,William Margolin,Richard Losick

doi:10.1128/mbio.01008-18

Abstract

ABSTRACTZipA is an essential cell division protein in Escherichia coli. Together with FtsA, ZipA tethers dynamic polymers of FtsZ to the cytoplasmic membrane, and these polymers are required to guide synthesis of the cell division septum. This dynamic behavior of FtsZ has been reconstituted on planar lipid surfaces in vitro, visible as GTP-dependent chiral vortices several hundred nanometers in diameter, when anchored by FtsA or when fused to an artificial membrane binding domain. However, these dynamics largely vanish when ZipA is used to tether FtsZ polymers to lipids at high surface densities. This, along with some in vitro studies in solution, has led to the prevailing notion that ZipA reduces FtsZ dynamics by enhancing bundling of FtsZ filaments. Here, we show that this is not the case. When lower, more physiological levels of the soluble, cytoplasmic domain of ZipA (sZipA) were attached to lipids, FtsZ assembled into highly dynamic vortices similar to those assembled with FtsA or other membrane anchors. Notably, at either high or low surface densities, ZipA did not stimulate lateral interactions between FtsZ protofilaments. We also used E. coli mutants that are either deficient or proficient in FtsZ bundling to provide evidence that ZipA does not directly promote bundling of FtsZ filaments in vivo. Together, our results suggest that ZipA does not dampen FtsZ dynamics as previously thought, and instead may act as a passive membrane attachment for FtsZ filaments as they treadmill.

Highlights

IntroductionTogether with FtsA, ZipA tethers dynamic polymers of FtsZ to the cytoplasmic membrane, and these polymers are required to guide synthesis of the cell division septum
ZipA is an essential cell division protein in Escherichia coli
In Escherichia coli, the earliest event in the septum formation is the assembly of FtsZ, FtsA, and ZipA in the protoring, a discontinuous structure at midcell that serves as a scaffold for the rest of the divisome components [1, 2]

Summary

Introduction

Together with FtsA, ZipA tethers dynamic polymers of FtsZ to the cytoplasmic membrane, and these polymers are required to guide synthesis of the cell division septum This dynamic behavior of FtsZ has been reconstituted on planar lipid surfaces in vitro, visible as GTP-dependent chiral vortices several hundred nanometers in diameter, when anchored by FtsA or when fused to an artificial membrane binding domain. We use electron microscopy and confocal fluorescence imaging to show that one of the proteins required to attach FtsZ polymers to the membrane during E. coli cell division, ZipA, can promote dynamic swirls of FtsZ on a lipid surface in vitro. Through connections involving other divisome proteins that cross the cytoplasmic membrane, these treadmilling FtsZ protofilaments help to guide the septum synthesis machinery in concentric circles, resulting in inward growth of the septal wall until it closes and the daughter cells are separated [8, 9]

Methods

Results

Conclusion