Chlamydia trachomatis protein CT009 is a structural and functional homolog to the key morphogenesis component RodZ and interacts with division septal plane localized MreB

Abstract

Summary Cell division in Chlamydiae is poorly understood as apparent homologs to most conserved bacterial cell division proteins are lacking and presence of elongation (rod shape) associated proteins indicate non-canonical mechanisms may be employed. The rod-shape determining protein MreB has been proposed as playing a unique role in chlamydial cell division. In other organisms, MreB is part of an elongation complex that requires RodZ for proper function. A recent study reported that the protein encoded by ORF CT009 interacts with MreB despite low sequence similarity to RodZ. The studies herein expand on those observations through protein structure, mutagenesis, and cellular localization analyses. Structural analysis indicated that CT009 shares high level of structural similarity to RodZ, revealing the conserved orientation of two residues critical for MreB interaction. Substitutions eliminated MreB protein interaction and partial complementation provided by CT009 in RodZ deficient E. coli. Cellular localization analysis of CT009 showed uniform membrane staining in Chlamydia. This was in contrast to the localization of MreB, which was restricted to predicted septal planes. MreB localization to septal planes provides direct experimental observation for the role of MreB in cell division and supports the hypothesis that it serves as a functional replacement for FtsZ in Chlamydia.

Critical Role for the Unique N-Terminus of Chlamydial MreB in Directing Its Membrane Association and Interaction with Elements of the Divisome

“…As seen in Figure 1, we observed using super-resolution structured illumination microscopy (SIM) the polar localization of the major outer membrane protein (MOMP) in the budding daughter cell as previously reported(7). Consistent with its proposed role in division(8), MreB_6xH was localized in a band-like structure across the septum and not in puncta as previously reported(13, 16). Interestingly, when 3D reconstructions were assembled from the SIM images, we observed that MreB_6xH formed ring-like structures at the septum with areas of more intense signal (Fig.…”

“…Given our hypothesis for the role of chlamydial MreB in directing polarized division, we examined its localization during the first division of an RB. We were unable to detect endogenous MreB with the antibody previously used to image the distribution of MreB in Chlamydia (13). We then attempted to image wild-type and various truncation mutants of MreB using a GFP sandwich (SW) fusion strategy that, in E. coli , was reported to be functional(14) (N-or C-terminal fluorescent protein fusions with MreB display an artifactual localization(15)).…”

Peptidoglycan in obligate intracellular bacteria

“…Chlamydiales are amongst the few known bacteria that lack FtsZ, the bacterial tubulin homolog that organizes the divisome complex at midcell to direct septal peptidoglycan synthesis and facilitates cytokinesis (Busiek and Margolin, 2015). Evidence has been provided that the bacterial actin complex, composed of MreB actin and its regulator RodZ, partially substitute for the role of FtsZ in cytokinesis and spatial regulation of septal peptidoglycan synthesis Kemege et al, 2015;Liechti et al, 2016). After a complete replication cycle re-differentiation into elementary bodies takes place in response to unknown signals, and new elementary bodies are released from the cell by either lysis or extrusion.…”

Bacterial Cell Division: Nonmodels Poised to Take the Spotlight

“…This led to the model that peptidoglycan synthesis may drive cytokinesis in this organism (88). Indeed, in C. trachomatis and a related organism, MreB and RodZ (9), which are involved in spatially regulating peptidoglycan incorporation, localize to cell division sites (65, 71, 87). Interestingly, recent observations have suggested that, even in E. coli , FtsZ may not provide the force for membrane invagination and constriction during cell division and that peptidoglycan assembly may instead be the rate-limiting step that deforms the membrane (142), suggesting that cell wall-driven cytokinesis may be a widely conserved mechanism driving bacterial cell division.…”