ArsD was initially reported to be a trans-acting repressor of the arsRDABC operon, which confers resistance to arsenicals and antimonials in Escherichia coli [1]. It has since been shown to be a metallochaperone that delivers As(III) to ArsA (the catalytic subunit of the ArsAB pump encoded by arsRDABC), increasing its affinity for As(III) allowing resistance to environmental concentrations of arsenic [2,3]. ArsD has three conserved cysteines Cys(12), Cys(13), and Cys(18), which form a three sulfur-coordinated As(III) binding site that is essential for delivery of As(III) to, and activation of the ArsAB pump [2,3]. This family also includes ArsD homologues which do not contain the conserved CCxxxxC required for function.

1: Evidence for cooperativity between the four binding sites of dimeric ArsD, an As(III)-responsive transcriptional regulator. Li S, Rosen BP, Borges-Walmsley MI, Walmsley AR; J Biol Chem 2002;277:25992-26002. PMID:11980902

2: ArsD residues Cys12, Cys13, and Cys18 form an As(III)-binding site required for arsenic metallochaperone activity. Lin YF, Yang J, Rosen BP; J Biol Chem. 2007;282:16783-16791. PMID:17439954

3: The ArsD As(III) metallochaperone. Ajees AA, Yang J, Rosen BP; Biometals. 2011;24:391-399. PMID:21188475