CTP and parS coordinate ParB partition complex dynamics and ParA-ATPase activation for ParABS-mediated DNA partitioning
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Evaluation Summary:
This manuscript reports carefully executed experiments on the dynamics of ParA-ParB and ParB-ParB interactions. Two main findings are presented: a change in stoichiometry of ParA-ParB interactions upon ligand binding and ligand dependent DNA condensation by ParB. The work is solid, the conclusions are generally well supported by the data, however, the relevance of some of the findings could be established more directly.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)
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Abstract
ParABS partition systems, comprising the centromere-like DNA sequence parS , the parS -binding ParB-CTPase, and the nucleoid-binding ParA-ATPase, ensure faithful segregation of bacterial chromosomes and low-copy-number plasmids. F-plasmid partition complexes containing ParB F and parS F move by generating and following a local concentration gradient of nucleoid-bound ParA F . However, the process through which ParB F activates ParA F -ATPase has not been defined. We studied CTP- and parS F -modulated ParA F –ParB F complex assembly, in which DNA-bound ParA F -ATP dimers are activated for ATP hydrolysis by interacting with two ParB F N-terminal domains. CTP or parS F enhances the ATPase rate without significantly accelerating ParA F –ParB F complex assembly. Together, parS F and CTP accelerate ParA F –ParB F assembly without further significant increase in ATPase rate. Magnetic-tweezers experiments showed that CTP promotes multiple ParB F loading onto parS F -containing DNA, generating condensed partition complex-like assemblies. We propose that ParB F in the partition complex adopts a conformation that enhances ParB F –ParB F and ParA F –ParB F interactions promoting efficient partitioning.
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Reviewer #2 (Public Review):
The recent discovery of CTP as a co-factor for the ParB protein family has prompted the field to revisit all the experimental data and models on ParABS-mediated chromosome/plasmid segregation from the past 35 years. Some recent research has been performed to investigate ParB-CTP interaction and the roles of CTP on ParB spreading/sliding. However, the important roles of CTP on ParB-ParA interaction have not been investigated so far. This manuscript from Taylor et al is the first to investigate this important area, thus this work is timely and is very welcomed. I note that Mizuuchi et al proposed the ground-breaking "diffusion-ratchet" model of plasmid/chromosome segregation, and the latest findings in his manuscript here have very important implications for this model. The work here has been done rigorously; …
Reviewer #2 (Public Review):
The recent discovery of CTP as a co-factor for the ParB protein family has prompted the field to revisit all the experimental data and models on ParABS-mediated chromosome/plasmid segregation from the past 35 years. Some recent research has been performed to investigate ParB-CTP interaction and the roles of CTP on ParB spreading/sliding. However, the important roles of CTP on ParB-ParA interaction have not been investigated so far. This manuscript from Taylor et al is the first to investigate this important area, thus this work is timely and is very welcomed. I note that Mizuuchi et al proposed the ground-breaking "diffusion-ratchet" model of plasmid/chromosome segregation, and the latest findings in his manuscript here have very important implications for this model. The work here has been done rigorously; I have read it with much interest.
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Reviewer #1 (Public Review):
This manuscript by Taylor et al. carefully investigates (1) ParB-ParA and (2) ParB-ParB interactions in the F Plasmid SopABC system using microfluidics, TIRF microscopy and magnetic tweezers.
(1) The work shows that the activation of ParA ATP hydrolysis requires a dimer of ParA to bind to two protomers of ParB. Surprisingly, ParB can bind to ParA either using the two protomers of a single dimer or two protomers from distinct dimers. The former occurs in the absence of ligands, the latter upon addition of either CTP or parS DNA, thus presumably corresponding to the state of ParB found in the cells near a parS site. The authors suggest that this is crucial for the precise timing of ParA-ParB anchoring and release.
(2) Magnetic tweezer experiments demonstrate nucleotide-dependent compaction of DNA by ParB. This …
Reviewer #1 (Public Review):
This manuscript by Taylor et al. carefully investigates (1) ParB-ParA and (2) ParB-ParB interactions in the F Plasmid SopABC system using microfluidics, TIRF microscopy and magnetic tweezers.
(1) The work shows that the activation of ParA ATP hydrolysis requires a dimer of ParA to bind to two protomers of ParB. Surprisingly, ParB can bind to ParA either using the two protomers of a single dimer or two protomers from distinct dimers. The former occurs in the absence of ligands, the latter upon addition of either CTP or parS DNA, thus presumably corresponding to the state of ParB found in the cells near a parS site. The authors suggest that this is crucial for the precise timing of ParA-ParB anchoring and release.
(2) Magnetic tweezer experiments demonstrate nucleotide-dependent compaction of DNA by ParB. This compaction is strictly parS-sequence dependent and robust even at elevated DNA extension force (5 pN) and at relatively low ParB concentrations. This implies ParB dimer-ParB dimer interactions exclusively on parS DNA.
The conclusions are generally well supported by the data. Few control experiments are suggested.
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Evaluation Summary:
This manuscript reports carefully executed experiments on the dynamics of ParA-ParB and ParB-ParB interactions. Two main findings are presented: a change in stoichiometry of ParA-ParB interactions upon ligand binding and ligand dependent DNA condensation by ParB. The work is solid, the conclusions are generally well supported by the data, however, the relevance of some of the findings could be established more directly.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)
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