The efficient segregation of replicated genetic material is an essential step for cell division. Bacterial cells use several evolutionarily-distinct genome segregation systems, the most common of which is the type I Par system. It consists of an adapter protein, ParB, that binds to the DNA cargo via interaction with the parS DNA sequence; and an ATPase, ParA, that binds nonspecific DNA and mediates cargo transport. However, the molecular details of how this system functions are not well understood. Here, we report the cryo-EM structure of the Vibrio cholerae ParA2 filament bound to DNA, as well as the crystal structures of this protein in various nucleotide states.
Fig: Structure of the ParA2vc dimer: a Schematic representation of the chromosome segregation systems for the V. cholerae chromosome 1 (top), and chromosome II (bottom). The centromere-like partition site is in yellow (parS), the adapter parS binding protein is in green (ParB) and the NTPase protein is in blue (ParA), with the additional N-terminal domain (NTD) found only in ChrII shown. b Cartoon representation of the ParA2vc crystal structure, in rainbow coloring, starting from blue at the N terminus, to red at the C terminus. c The crystallographic dimer of ParA2vc shown from the side (left) and top (right), with the two symmetry-related pairs in blue and magenta, respectively. The NTD and helix 1 are indicated.
These structures show that ParA forms a left-handed filament on DNA, stabilized by nucleotide binding, and that ParA undergoes profound structural rearrangements upon DNA binding and filament assembly. Collectively, our data suggest the structural basis for ParA’s cooperative binding to DNA and the formation of high ParA density regions on the nucleoid.
Parker, A.V., Mann, D., Tzokov, S.B. et al. The structure of the bacterial DNA segregation ATPase filament reveals the conformational plasticity of ParA upon DNA binding. Nat Commun 12, 5166 (2021). https://doi.org/10.1038/s41467-021-25429-2