Biology subjects

McCausland, J. W.

Publications and source records attributed to McCausland, J. W..

4 recordsLinked to original sources

bioRxiv2022

Integration of cell wall synthesis activation and chromosome segregation during cell division in Caulobacter

To divide, bacteria must synthesize and remodel their peptidoglycan (PG) cell wall, a protective meshwork that maintains cell shape. FtsZ, a tubulin homolog, dynamically assembles into a midcell band, recruiting division proteins including the PG synthases FtsW and FtsI. FtsWI are activated to synthesize PG and drive constriction at the appropriate time and place, however their activation pathway remains unresolved. In Caulobacter crescentus, FtsWI activity requires FzlA, an essential FtsZ-binding protein. Through time-lapse imaging and single-molecule tracking of C. crescentus FtsW and FzlA in perturbed genetic backgrounds, we demonstrate that FzlA is a limiting constriction activation factor that converts inactive, fast-moving FtsW to an active, slow-moving state. We find that FzlA interacts with the DNA translocase FtsK, and place FtsK genetically in a pathway with FzlA and FtsWI. Misregulation of the FzlA-FtsK-FtsWI pathway leads to heightened DNA damage and cell death. We propose that FzlA integrates the FtsZ ring, chromosome segregation, and PG synthesis to ensure robust and timely constriction during Caulobacter division.

microbiology↗

bioRxiv2021

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

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 FtsZs 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.

microbiology↗

bioRxiv2019

Treadmilling FtsZ polymers drive the directional movement of sPG-synthesis enzymes via a Brownian ratchet mechanism

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 FtsZs 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 FtsZs 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 enzymes diffusion and FtsZs 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.

biophysics↗

bioRxiv2019

FtsW exhibits distinct processive movements driven by either septal cell wall synthesis or FtsZ treadmilling in E. coli

During bacterial cell division, synthesis of new septal peptidoglycan (sPG) is crucial for successful cytokinesis and cell pole morphogenesis. FtsW, a SEDS (Shape, Elongation, Division and Sporulation) family protein and an indispensable component of the cell division machinery in all walled bacterial species, was recently identified in vitro as a new monofunctional peptidoglycan glycosyltransferase (PGTase). FtsW and its cognate monofunctional transpeptidase (TPase) class B penicillin binding protein (PBP3 or FtsI in E. coli) may constitute the essential, bifunctional sPG synthase specific for new sPG synthesis. Despite its importance, the septal PGTase activity of FtsW has not been documented in vivo. How its activity is spatiotemporally regulated in vivo has also remained unknown. Here we investigated the septal PGTase activity and dynamics of FtsW in E. coli cells using a combination of single-molecule imaging and genetic manipulations. We show that FtsW exhibits robust activity to incorporate an N-acetylmuramic acid analog at septa in the absence of other known PGTases, confirming FtsW as the essential septum-specific PGTase in vivo. Notably, we identified two populations of processive moving FtsW molecules at septa. A fast-moving population is driven by the treadmilling dynamics of FtsZ and independent of sPG synthesis. A slow-moving population is driven by active sPG synthesis and independent of FtsZs treadmilling dynamics. We further identified that FtsN, a potential sPG synthesis activator, plays an important role in promoting the slow-moving, sPG synthesis-dependent population. Our results support a two-track model, in which inactive sPG synthase molecules follow the fast treadmilling "Z-track" to be distributed along the septum; FtsN promotes their release from the "Z-track" to become active in sPG synthesis on the slow "sPG-track". This model explains how the spatial information is integrated into the regulation of sPG synthesis activity and suggests a new mechanistic framework for the spatiotemporal coordination of bacterial cell wall constriction.

biophysics↗