Regensburg 2022 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 29: Biomaterials (joint session BP/CPP)

CPP 29.4: Talk

Wednesday, September 7, 2022, 16:15–16:30, H15

Partition complex structure arises from sliding and bridging — •Lara Connolley and Sean Murray — Max Planck Institute for Terrestrial Microbiology, Marburg, Germany

Chromosome segregation is vital for cell replication and in many bacteria is controlled by the ParABS system. A key part of this machinery is the association of ParB proteins to the parS-containing centromeric region to form the partition complex. Despite much work, the formation and structure of this nucleoprotein complex has remained unclear. However, it was recently discovered that CTP binding allows ParB dimers to entrap and slide along the DNA, as well as leading to more efficient condensation through ParB-ParB-mediated DNA bridging. Here, we use stiff polymer simulations to show how these properties of sliding and bridging can explain partition complex formation. We find that dynamic ParB bridges condense the DNA through the formation of two structures, hairpins and helices. In separate stochastic simulations, we show that ParB sliding accurately predicts the experimentally measured multi-peaked binding profile of Caulobacter crescentus, indicating that bridging and other potential roadblocks are sufficiently short-lived that they do not hinder ParB spreading. Indeed, upon coupling the two simulation frameworks into a unified sliding and bridging polymer model, we find that short lived ParB bridges do not hinder ParB sliding from the parS sites, and can reproduce the binding profile of ParB as well as the overall condensation of the nucleoprotein complex. Overall, our model clarifies the mechanism of partition complex formation and predicts its fine structure.