A Super-Resolution Study of the Structural Organization of the E. Coli FTSZ-Ring by ZapA and ZapB

Abstract

The first step in E. coli cell division is the localization of the FtsZ protein at midcell, where it polymerizes into a ring-like structure called the Z-ring. FtsZ is widely conserved throughout bacteria and is a structural homolog of eukaryotic tubulin. Understanding the organization of the Z-ring will provide insight into the force generation mechanism of bacterial cell division.In our previous work we used a super-resolution imaging method, photoactivated localization microscopy (PALM), to characterize the arrangement of FtsZ protofilaments inside the Z-ring1. We showed that the Z-ring is likely composed of a loose association of protofilaments overlapping in both the circumferential and radial direction of the Z-ring. Given that FtsZ protofilaments exhibit a low intrinsic self-interaction, how they are associated in vivo remains unknown.Recently a family of Z-ring associated proteins (Zap) have been shown to promote FtsZ polymerization in vitro and Z-ring formation in vivo. In this study, we investigated how ZapA and ZapB affect the organization of the Z-ring.We used live-cell PALM imaging to characterize the structure of the Z-ring in the absence of ZapA and ZapB. We found that in the absence of ZapA or ZapB, FtsZ adopts a variety of non-native structures characterized by a fractured appearance containing dispersed clusters of FtsZ. Similar FtsZ clusters have been observed to precede wild-type Z-ring assembly and are likely composed of multiple FtsZ protofilaments. Comparison of the FtsZ clusters observed in ΔzapA and ΔzapB to those observed in wild-type suggest that ZapA and ZapB may function to promote Z-ring assembly by corralling and consolidating higher-ordered FtsZ groupings.[1] G. Fu, T. Huang, J. Buss, C. Coltharp, Z. Hensel, J. Xiao, PLoS One 2010, 5, e12680.