FtsN activates septal cell wall synthesis by forming a processive complex with the septum-specific peptidoglycan synthase in E. coli

Abstract

The FtsN protein of Escherichia coli and other proteobacteria is an essential and highly conserved bitopic membrane protein that triggers the inward synthesis of septal peptidoglycan (sPG) during cell division. Previous work has shown that the activation of sPG synthesis by FtsN involves a series of interactions of FtsN with other divisome proteins and the cell wall. Precisely how FtsN achieves this role is unclear, but a recent study has shown that FtsN promotes the relocation of the essential sPG synthase FtsWI from an FtsZ-associated track (where FtsWI is inactive) to an sPG-track (where FtsWI engages in sPG synthesis). Whether FtsN works by displacing FtsWI from the Z-track or capturing/retaining FtsWI on the sPG-track is not known. Here we use single-molecule imaging and genetic manipulation to investigate the organization and dynamics of FtsN at the septum and how they are coupled to sPG synthesis activity. We found that FtsN exhibits a spatial organization and dynamics distinct from those of the FtsZ-ring. Single FtsN molecules move processively as a single population with a speed of ~ 9 nm s-1, similar to the speed of active FtsWI molecules on the sPG-track, but significantly different from the ~ 30 nm s-1 speed of inactive FtsWI molecules on the FtsZ-track. Furthermore, the processive movement of FtsN is independent of FtsZ's treadmilling dynamics but driven exclusively by active sPG synthesis. Importantly, only the essential domain of FtsN, a three-helix bundle in the periplasm, is required to maintain the processive complex containing both FtsWI and FtsN on the sPG-track. We conclude that FtsN activates sPG synthesis by forming a processive synthesis complex with FtsWI exclusively on the sPG-track. These findings favor a model in which FtsN captures or retains FtsWI on the sPG-track rather than one in which FtsN actively displaces FtsWI from the Z-track.

Dynamic localisation of DamX regulates bacterial filamentation and division during UPEC dispersal from host cells

“…Our single-molecule data suggest that mEos3.2-DamX assembles into rather broad rings at the quarter or half positions along filaments, consistent with the expected locations of division, and then condenses leading up to constriction, where mEos3.1-DamX rings showed very similar dimensions as those formed by related cell division components during E. coli division 28,39,40 . Lastly, mEos3.2-DamX remained assembled at the division septum until after the envelopes had visibly separated, suggesting a role for DamX in sPG regulation until the new cell wall is completed.…”

Cell cycle-dependent recruitment of FtsN to the divisome in Escherichia coli

“…This finding can be explained if FtsN in the septal ring is not physically linked to FtsZ protofilaments. Evidence for decoupling FtsN and FtsZ protofilaments has also been documented in other measurements where their localization in the radial direction was examined (55) and from recent single-molecule studies (62).…”

An Updated Model of the Divisome: Regulation of the Septal Peptidoglycan Synthesis Machinery by the Divisome

“…The dynamics during the division of FtsZ and FtsA differ from those of FtsW, FtsI and FtsN. The speed of FtsZ filaments and FtsA proteins has been reported to be close to 30 nm/s, while the average speed of FtsWI is closer to 20 nm/s, and FtsN moves even slower at roughly 9 nm/s [ 29 , 30 , 90 , 91 ]. FtsWI appears to have slow and fast-moving populations that respectively correlate with FtsN and FtsZ treadmilling dynamics.…”

“…The fast-moving population is coupled to FtsZ treadmilling dynamics, while FtsN promotes the slow-moving population [ 29 ]. The dynamics of the slow-moving population and FtsN are affected by the rate of sPG synthesis, as the inhibition of sPG synthesis diminishes FtsN movement and the slow-moving FtsW population [ 29 , 30 ]. Overall, this suggests a fast-moving assembly track around the septum controlled by FtsZ treadmilling, and a slow-moving synthesis track promoted by FtsN.…”

“…This includes the discovery of a PG synthesis track moving independently from FtsZ-ring dynamics. The synthesis track is indicated by multiple studies where the dynamics of FtsN and FtsWI follow the rate of sPG synthesis, which differs from FtsZ treadmilling dynamics [ 29 , 30 ]. Interestingly, the FtsZ-ring appears to be involved in the spatial distribution of the synthesis track, which is proposed to be linked to the activity of the semi-essential FtsEX subcomplex.…”