Toxin-antitoxin (TA) systems play critical roles in the environment adaptation of bacteria. Allosteric coupling between the N-terminal DNA-binding domain and the C-terminal toxin-binding domain of antitoxins contributes to conditional cooperativity in the functioning of type II TA. Herein, using circular dichroism (CD), nuclear magnetic resonance (NMR), X-ray crystallography, and size exclusion chromatography (SEC), the structure and DNA binding of CopAso, a newly identified type II antitoxin in Shewanella oneidensis, were investigated. Our data show that CopAso is a typical RHH antitoxin with an ordered N-terminal domain and a disordered C-terminal domain, and furthermore indicate that the C terminal domain facilitates DNA binding of the N-terminal domain, which in turn induces the C-terminal domain to fold and associate. (C) 2019 Elsevier Inc. All rights reserved.