Fig. 7: Model of the ParA-ParB interaction.
From: Molecular basis of ParA ATPase activation by the CTPase ParB during bacterial chromosome segregation
a Role of the ParA-ParB interaction in DNA segregation. ParB clamps are loaded onto the centromere region and form a densely packed partition complex. ParA dimers, by contrast, diffuse across the nucleoid in a low-DNA-affinity state, which ensures a steady flux of dimers towards the partition complex. Closed ParB clamps interact with diffusible DNA-bound ParA dimers, forming a tethering complex that links the partition complex to the nucleoid. Cooperative interactions between the ParB- and DNA-binding sites stabilize the tethering complex and thus enables it to harness the elastic dynamics of chromosomal DNA loops for partition complex movement. The transition to this locked state involves structural rearrangements at the catalytic site of ParA that stimulate its ATPase activity, thereby limiting the lifetime of the tethers. ATP hydrolysis then leads to the dissociation of ParA and its release from both ParB and DNA, allowing the handover of the partition complex to adjacent DNA-bound ParA dimers. b Structural model of the M. xanthus ParA-ParB tethering complex. Shown is a model of a ParB dimer loaded onto parS-containing DNA (green) and interacting with a DNA (pink)-bound ParA dimer. ATP is shown in orange, Mg2+ in green. The ParB2-parS and ParA2-(ParB1-20)2 complexes were modeled separately with AlphaFold 3126 and then joined using UCSF-Chimera103. The DNA molecule bound to the ParA dimer was fitted into the model based on a superimposition of the predicted ParA2-(ParB1-20)2 complex with the crystal structure of a DNA-bound H. pylori ParA-D41A•ADP dimer (PDB: 6IUD35).
