Department of Chemistry, University of Sheffield, Sheffield, United Kingdom
Frank Sobott
Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, Antwerpen, Belgium; Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom; School of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom
Heath Murray
Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle, United Kingdom
Matthew P Crump
School of Chemistry, University of Bristol, Bristol, United Kingdom
Fernando Moreno-Herrero
Department of Macromolecular Structures, Centro Nacional de Biotecnologia, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
The ParB protein forms DNA bridging interactions around parS to condense DNA and earmark the bacterial chromosome for segregation. The molecular mechanism underlying the formation of these ParB networks is unclear. We show here that while the central DNA binding domain is essential for anchoring at parS, this interaction is not required for DNA condensation. Structural analysis of the C-terminal domain reveals a dimer with a lysine-rich surface that binds DNA non-specifically and is essential for DNA condensation in vitro. Mutation of either the dimerisation or the DNA binding interface eliminates ParB-GFP foci formation in vivo. Moreover, the free C-terminal domain can rapidly decondense ParB networks independently of its ability to bind DNA. Our work reveals a dual role for the C-terminal domain of ParB as both a DNA binding and bridging interface, and highlights the dynamic nature of ParB networks in Bacillus subtilis.