Structural and biochemical analyses of Caulobacter crescentus ParB reveal the role of its N-terminal domain in chromosome segregation

The tripartite ParA-ParB- complex ensures faithful chromosome segregation in the majority of bacterial species. ParB nucleates on a centromere-like site and spreads to neighboring DNA to form a network of protein-DNA complexes. This nucleoprotein network interacts with ParA to partition the locus, hence the chromosome to each daughter cell. Here, we determine the co-crystal structure of a C-terminal domain truncated ParB- complex from , and show that its N-terminal domain adopts alternate conformations. The multiple conformations of the N-terminal domain might facilitate the spreading of ParB on the chromosome. Next, using ChIP-seq we show that ParBs from different bacterial species exhibit variation in their intrinsic capability for spreading, and that the N-terminal domain is a determinant of this variability. Finally, we show that the C-terminal domain of ParB possesses no or weak non-specific DNA-binding activity. Engineered ParB variants with enhanced non-specific DNA-binding activity condense DNA but do not spread further than wild-type . Taken all together, our results emphasize the role of the N-terminal domain in ParB spreading and faithful chromosome segregation in .