Functional and structural characterization of AntR, an Sb(III) responsive transcriptional repressor

Area of Science:

• Microbiology
• Structural Biology
• Environmental Science

Background:

• The ant operon in *Comamonas testosterone* JL40 provides resistance to Sb(III).
• Transcriptional regulation of the ant operon is mediated by AntR, a metalloid-responsive repressor from the ArsR/SmtB family.

Purpose of the Study:

• To purify and characterize the *C. testosterone* AntR protein.
• To determine the structure and Sb(III) binding properties of AntR.

Main Methods:

• Protein purification and characterization of AntR from *C. testosterone*.
• X-ray crystallography to solve the 3D structure of AntR at 2.1 Å resolution.
• Metalloid response assays to determine AntR's binding selectivity.

Main Results:

• AntR was purified and characterized, showing a response order of Sb(III) = methylarsenite (MAs(III)) >> arsenite (As(III)).
• The homodimeric structure of AntR was solved, revealing a classical ArsR/SmtB topology.
• Five cysteine residues were identified, with specific pairs proposed to form two Sb(III) binding sites.

Conclusions:

• This work presents the first structural and binding data for a transcriptional repressor highly selective for environmental antimony.
• The findings elucidate the molecular basis of antimony resistance in *C. testosterone*.
• The characterized AntR provides a model for understanding metalloid-responsive regulation.