The structural basis for dynamic DNA binding and bridging interactions which condense the bacterial centromere.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The ParB protein is crucial for bacterial chromosome segregation by forming DNA networks around parS sites.
• The precise molecular mechanisms governing ParB network formation and DNA condensation remain incompletely understood.

Purpose of the Study:

• To elucidate the molecular mechanisms of ParB-mediated DNA condensation and network formation.
• To investigate the distinct roles of the central and C-terminal domains of ParB in DNA binding and condensation.

Main Methods:

• Structural analysis of the ParB C-terminal domain.
• In vitro DNA binding and condensation assays.
• In vivo studies using ParB-GFP fusion proteins in Bacillus subtilis.

Main Results:

• The central DNA binding domain anchors ParB at parS but is dispensable for DNA condensation.
• The C-terminal domain dimer forms a lysine-rich surface essential for non-specific DNA binding and in vitro DNA condensation.
• Mutations in dimerization or DNA binding interfaces disrupt in vivo ParB-GFP foci formation.
• The free C-terminal domain can rapidly decondense ParB networks, independent of DNA binding.

Conclusions:

• The ParB C-terminal domain plays a dual role in DNA binding and bridging, facilitating DNA condensation.
• ParB network dynamics are essential for bacterial chromosome organization and segregation in Bacillus subtilis.