Abstract
FtsZ, a highly conserved bacterial tubulin GTPase homolog, is a central component of the cell division machinery in nearly all walled bacteria. FtsZ polymerizes at the future division site and recruits greater than 30 proteins to assemble into a macromolecular complex termed the divisome. Many of these divisome proteins are involved in septal cell wall peptidoglycan (sPG) synthesis. Recent studies found that FtsZ polymers undergo GTP hydrolysis-coupled treadmilling dynamics along the circumference the division site, driving the processive movement of sPG synthesis enzymes. How FtsZ’s treadmilling drives the directional transport of sPG enzymes and what its precise role is in bacterial cell division are unknown. Combining theoretical modeling and experimental testing, we show that FtsZ’s treadmilling drives the directional movement of sPG-synthesis enzymes via a Brownian ratchet mechanism, where the shrinking end of FtsZ polymers introduces an asymmetry to rectify diffusions of single sPG enzymes into persistent end-tracking movement. Furthermore, we show that the processivity of this directional movement is dependent on the binding potential between FtsZ and the enzyme, and hinges on the balance between the enzyme’s diffusion and FtsZ’s treadmilling speed. This interplay could provide a mechanism to control the level of available enzymes for active sPG synthesis both in time and space, explaining the distinct roles of FtsZ treadmilling in modulating cell wall constriction rate observed in different bacterial species.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
1) We extended our analysis of FtsZ-mediated sPG synthesis to two other bacterial systems (B. subtilis and S. pneumoniae) in addition to E. coli. Figure 5 is reflected with this update. 2) We examined an alternative mechanism by which the motion of sPG synthases is coupled to the growing end of a treadmilling FtsZ polymer. See supplemental Figure 1. 3) We expanded on an additional control scheme for how different bacterial species could use to harvest the same FtsZ treadmilling dynamics to allow for different sPG cell wall synthesis needs. Specifically, we examined the stoichiometry of sPG synthases per FtsZ filament.