VIBRIO CHOLERAE PARD2:PARE2 TOXIN-ANTITOXIN COMPLEX STRUCTURE REVEALS A SINGULAR CONFORMATION

The Vibrio cholerae parDE2 chromosomal locus encodes a type II TA system that shows a modest similarity to the parDE operon in the RK2 plasmid. ParE2,
like plasmid RK2-encoded ParE, targets DNA gyrase, an essential enzyme that is also the target of quinolone antibacterial agents (Yuan et al., 2010).
Denaturant induced dissociation of the pre-purified ParD2:ParE2 complex yields pure separate components, which are currently being used to characterize
ParE2 interactions with both DNA gyrase and ParD2. The crystal structure of ParD2 shows, in the absence of its toxin, a hexadecamer, a result that is also
confirmed by SAXS. Native mass spectrometry analysis shows an unusual 6:2 stoichiometry for the ParD2:ParE2 complex in solution, which was also
confirmed by SAXS. Crystals of the complex diffract to 2.9 Å resolution and the structure was successfully determined by molecular replacement.
ParD2:ParE2 complex is present in a 6:2 antitoxin:toxin stoichiometry, in which the C-terminal region of one ParD2 monomer interacts with a ParE2 toxin,
while its N-terminal region is involved in interactions with two other ParD2 monomers, one of which then dimerizes with a ParD2 from another 3:1
ParD2:ParE2 association, to constitute the 6:2 stoichiometry that was detected in native mass spectrometry analysis and SAXS. This structure reveals the
binding mode of ParD2 to its V. cholerae toxin and constitutes the first example of a structure of one of the three RK2-plasmid ParE homologues present in
chromosome II of the human pathogen V. cholerae.