ORCID Profile
0000-0002-2104-5430
Current Organisation
University of Oxford
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Publisher: Springer Science and Business Media LLC
Date: 06-10-2016
DOI: 10.1038/SREP33357
Abstract: Bacterial chromosomes are most often circular DNA molecules. This can produce a topological problem a genetic crossover from homologous recombination results in dimerization of the chromosome. A chromosome dimer is lethal unless resolved. A site-specific recombination system catalyses this dimer-resolution reaction at the chromosomal site dif . In Escherichia coli , two tyrosine-family recombinases, XerC and XerD, bind to dif and carry out two pairs of sequential strand exchange reactions. However, what makes the reaction unique among site-specific recombination reactions is that the first step, XerD-mediated strand exchange, relies on interaction with the very C-terminus of the FtsK DNA translocase. FtsK is a powerful molecular motor that functions in cell ision, co-ordinating ision with clearing chromosomal DNA from the site of septation and also acts to position the dif sites for recombination. This is a model system for unlinking, separating and segregating large DNA molecules. Here we describe the molecular detail of the interaction between XerD and FtsK that leads to activation of recombination as deduced from a co-crystal structure, biochemical and in vivo experiments. FtsKγ interacts with the C-terminal domain of XerD, above a cleft where XerC is thought to bind. We present a model for activation of recombination based on structural data.
Publisher: American Society for Microbiology
Date: 31-12-2013
Abstract: Bacterial cell ision initiates with the formation of a ring-like structure at the cell center composed of the tubulin homolog FtsZ (the Z-ring), which acts as a scaffold for the assembly of the cell ision complex, the isome. Previous studies have suggested that the isome is initially composed of FtsZ polymers stabilized by membrane anchors FtsA and ZipA, which then recruit the remaining ision proteins. The MinCDE proteins prevent the formation of the Z-ring at poles by oscillating from pole to pole, thereby ensuring that the concentration of the Z-ring inhibitor, MinC, is lowest at the cell center. We show that prior to septum formation, the early- ision proteins ZipA, ZapA, and ZapB, along with FtsZ, assemble into complexes that counter-oscillate with respect to MinC, and with the same period. We propose that FtsZ molecules distal from high concentrations of MinC form relatively slowly diffusing filaments that are bound by ZapAB and targeted to the inner membrane by ZipA or FtsA. These complexes may facilitate the early stages of isome assembly at midcell. As MinC oscillates toward these complexes, FtsZ oligomerization and bundling are inhibited, leading to shorter or monomeric FtsZ complexes, which become less visible by epifluorescence microscopy because of their rapid diffusion. Reconstitution of FtsZ-Min waves on lipid bilayers shows that FtsZ bundles partition away from high concentrations of MinC and that ZapA appears to protect FtsZ from MinC by inhibiting FtsZ turnover. IMPORTANCE A big issue in biology for the past 100 years has been that of how a cell finds its middle. In Escherichia coli , over 20 proteins assemble at the cell center at the time of ision. We show that the MinCDE proteins, which prevent the formation of septa at the cell pole by inhibiting FtsZ, drive the counter-oscillation of early-cell- ision proteins ZapA, ZapB, and ZipA, along with FtsZ. We propose that FtsZ forms filaments at the pole where the MinC concentration is the lowest and acts as a scaffold for binding of ZapA, ZapB, and ZipA: such complexes are disassembled by MinC and reform within the MinC oscillation period before accumulating at the cell center at the time of ision. The ability of FtsZ to be targeted to the cell center in the form of oligomers bound by ZipA and ZapAB may facilitate the early stages of isome assembly.
Publisher: Oxford University Press (OUP)
Date: 02-03-2011
DOI: 10.1093/NAR/GKR078
Publisher: Proceedings of the National Academy of Sciences
Date: 11-11-2013
Abstract: Newly replicated circular chromosomes are topologically linked. XerC/XerD- dif (XerCD- dif )–FtsK recombination acts in the replication termination region of the Escherichia coli chromosome to remove links introduced during homologous recombination and replication, whereas Topoisomerase IV removes replication links only. Based on gel mobility patterns of the products of recombination, a stepwise unlinking pathway has been proposed. Here, we present a rigorous mathematical validation of this model, a significant advance over prior biological approaches. We show definitively that there is a unique shortest pathway of unlinking by XerCD- dif –FtsK that strictly reduces the complexity of the links at every step. We delineate the mechanism of action of the enzymes at each step along this pathway and provide a 3D interpretation of the results.
Publisher: Cold Spring Harbor Laboratory
Date: 23-07-2013
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for David Sherratt.