Structures and Dynamics of the E. Coli FtsZ-Ring and its Associated Proteins during Cell Division Revealed by Superresolution Imaging

Abstract

Cell division is essential for all organisms. In prokaryotes, the FtsZ protein, a tubulin-like GTPase, plays a central role. FtsZ is highly conserved across bacterial species and has been identified as a novel drug target for antimicrobial therapy. In vivo FtsZ assembles into a supramolecular ring-like structure (Z-ring) at the leading edge of the invaginating membrane. The Z-ring serves as an essential scaffold to recruit all other division proteins and generates contractile force for cytokinesis. Despite the essential role of the Z-ring in bacterial cell division, it is not known what the structure of the Z-ring is or how the contractile force is generated.We employ the newly developed single-molecule-based superresolution imaging technique to characterize the in vivo structure of the cell division apparatus in E. coli. We discovered that the Z-ring of E. coli adopts a compressed helical conformation in addition to the expected ring-conformation. The Z-ring is likely composed of a loose bundle of FtsZ protofilaments that randomly overlap with each other in both longitudinal and radial directions of the cell. We also observed the structural dynamics of the Z-ring during cell division and found that the Z-ring goes through a condensation phase before it finally collapses toward the end of septum closure. Furthermore, we extend the work into other cell division proteins that play important roles in maintaining the structural integrity of the cell division ring. We imaged two Z-ring binding proteins, ZapA and ZapB, and characterized their influence on the structure of the Z-ring. Our results provide significant insight into the spatial organization of the bacterial cell division apparatus and open the door for further investigations of structure-function relationships and cell cycle-dependent regulation of the Z-ring.