Influence of FtsZ GTPase activity and concentration on nanoscale Z‐ring structure in vivo revealed by three‐dimensional Superresolution imaging

FtsZ is an essential bacterial cytoskeletal protein that assembles into a ring‐like structure (Z‐ring) at midcell to carry out cytokinesis. In vitro, FtsZ exhibits polymorphism in polymerizing into different forms of filaments based on its GTPase activity, concentration, and buffer condition. In vivo, the Z‐ring appeared to be punctate and heterogeneously organized, although continuous, homogenous Z‐ring structures have also been observed. Understanding how the Z‐ring is organized in vivo is important because it provides a structural basis for the functional role of the Z‐ring in cytokinesis. Here, we assess the effects of both GTPase activity and FtsZ concentration on the organization of the Z‐ring in vivo using three‐dimensional (3D) superresolution microscopy. We found that the Z‐ring became more homogenous when assembled in the presence of a GTPase‐deficient mutant, and upon overexpression of either wt or mutant FtsZ. These results suggest that the in vivo organization of the Z‐ring is largely dependent on the intrinsic polymerization properties of FtsZ, which are significantly influenced by the GTPase activity and concentration of FtsZ. Our work provides a unifying theme to reconcile previous observations of different Z‐ring structures, and supports a model in which the wt Z‐ring comprises loosely associated, heterogeneously distributed FtsZ clusters. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 725–734, 2016.