Abstract
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. 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.
Highlights
The efficient segregation of replicated genetic material is an essential step for cell division
We have reported the structure of the ParA2vc protein, in three states: apo, nucleotide-bound (ADP) and in a filamentous complex with nucleotide and DNA
We show that the N-terminal helix-turn-helix domain (NTD) forms additional contacts with the DNA, revealing differences between type Ia and type Ib ParA proteins
Summary
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. 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. The type I segregation system locus encodes the ATPase ParA; an adapter protein, ParB; and contains a centromere-like parS site(s). Biochemical studies have shown that ParB stimulates ParA’s ATPase activity, promoting its dissociation from DNA15–18, via a conserved arginine finger-like motif[19]
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