Access

Article

Nature Chemical Biology 3, 60–68 (1 January 2007) | doi:10.1038/nchembio844

CsoR is a novel Mycobacterium tuberculosis copper-sensing transcriptional regulator

Tong Liu , Arati Ramesh , Zhen Ma , Sarah K Ward , Limei Zhang , Graham N George , Adel M Talaat , James C Sacchettini & David P Giedroc

Copper is an essential element that becomes highly cytotoxic when concentrations exceed the capacity of cells to sequester the ion. Here, we identify a new copper-specific repressor (CsoR) of a copper-sensitive operon (cso) in Mycobacterium tuberculosis (Mtb) that is representative of a large, previously uncharacterized family of proteins (DUF156). Electronic and X-ray absorption spectroscopies reveal that CsoR binds a single-monomer mole equivalent of Cu(I) to form a trigonally coordinated (S2N) Cu(I) complex. The 2.6-|[Aring]| crystal structure of copper-loaded CsoR shows a homodimeric antiparallel four-helix bundle architecture that represents a novel DNA-binding fold. The Cu(I) is coordinated by Cys36, Cys65|[prime]| and His61|[prime]| in a subunit bridging site. Cu(I) binding negatively regulates the binding of CsoR to a DNA fragment encompassing the operator-promoter region of the Mtb cso operon; this results in derepression of the operon in Mtb and the heterologous host Mycobacterium smegmatis. Substitution of Cys36 or His61 with alanine abolishes Cu(I)- and CsoR-dependent regulation in vivo and in vitro. Potential roles of CsoR in Mtb pathogenesis are discussed.