Entropic pressure controls oligomerization ofVibrio choleraeParD2 antitoxin

ParD2 is the antitoxin component of the parDE2 toxin-antitoxin module from Vibrio cholerae and consists of an ordered DNA binding domain followed by an intrinsically disordered ParE-neutralizing domain. In absence of the C-terminal IDP domain, VcParD2 crystallizes as a doughnut-shaped hexadecamer formed by the association of eight dimers. This assembly is stabilized via hydrogen bonds and salt bridges rather than hydrophobic contacts. In solution, oligomerization of the full-length protein is restricted to a stable, open 10-mer or 12-mer, likely as a consequence of entropic pressure from the IDP tails. The relative positioning of successive VcParD2 dimers mimics the arrangement of Streptococcus agalactiae CopG dimers on their operator and allows for an extended operator to wrap around the VcParD2 oligomer.