Structural and functional characterization of the transcriptional repressor CsoR from Thermus thermophilus HB8

Abstract

The TTHA1719 gene from Thermus thermophilus HB8 encodes an orthologue of the copper-sensing transcriptional repressor CsoR. X-ray crystal structure analysis of T. thermophilus CsoR indicated that it forms a homotetramer. The structures of the CsoR monomer and dimer are similar to those of Mycobacterium tuberculosis CsoR. In the absence of copper ions, T. thermophilus CsoR bound to the promoter region of the copper-sensitive operon copZ-csoR-copA, which encodes the copper chaperone CopZ, CsoR and the copper efflux P-type ATPase CopA, to repress their expression, while in the presence of approximately an equal amount of copper ion, CsoR was released from the DNA, to allow expression of the downstream genes. Both Cu(II) and Cu(I) ions could bind CsoR, and were effective for transcriptional derepression. Additionally, CsoR could also sense various other metal ions, such as Zn(II), Ag(I), Cd(II) and Ni(II), which led to transcriptional derepression. The copper-binding motif of T. thermophilus CsoR contains C-H-H, while those of most orthologues contain C-H-C. The X-ray crystal structure of T. thermophilus CsoR suggests that a histidine residue in the N-terminal domain is also involved in metal-ion binding; that is, the binding motif could be H-C-H-H, like that of Escherichia coli RcnR, which binds Ni(II)/Co(II). The non-conserved H70 residue in the metal-binding motif of T. thermophilus CsoR is important for its DNA-binding affinity and metal-ion responsiveness.

Copper-responsive gene regulation in bacteria

“…Experimental evidence for copper-responsive gene regulation by CsoR in proteobacteria and cyanobacteria is lacking to date. However, CsoR has been shown to control copper homeostasis in Thermus thermophilus belonging to the phylum Deinococcus-Thermus, which is only distantly related to proteobacteria and Grampositive species (Sakamoto et al, 2010). Apparently, CsoR homologues are the primary one-component copperresponsive regulators in prokaryotes lacking CueR (Liu et al, 2007).…”

“…T. thermophilus harbours the copZ-csoR-copA operon, which is repressed by CsoR under copper-limiting conditions (Sakamoto et al, 2010). In vitro, T. thermophilus CsoR is very promiscuous and binds various metal ions, including Cu + , Cu 2+ , Zn 2+ , Cd 2+ , Ag + and Ni 2+ , all of which release CsoR from the copZ promoter.…”

“…Gene regulation by copper proteobacteria (Sakamoto et al, 2010). Future studies are required to clarify the roles of predicted CsoR homologues in proteobacteria.…”

“…tuberculosis, Streptomyces lividans and T. thermophilus (Dwarakanath et al, 2012;Liu et al, 2007;Sakamoto et al, 2010). Mt-CsoR forms homodimers, while Sl-CsoR and Tt-CsoR form tetramers.…”

Control of Copper Resistance and Inorganic Sulfur Metabolism by Paralogous Regulators in Staphylococcus aureus

“…tuberculosis CsoR 6 (copper-sensitive operon repressor) is a founding member of large family of regulators now known collectively to respond to Cu(I), Ni(II), and perhaps other stressors, the structural basis of which is not fully understood (11, 12). All CsoR family proteins lack a known canonical DNA binding domain and are projected to adopt the flat disc-shaped dimer of dimers homotetrameric structure characteristic of Cu(I)-sensing CsoRs, with individual dimers consisting of an antiparallel four-helix bundle flanked by a C-terminal ␣3 helix (13,14). Two cysteine residues on opposite subunits within a dimer make coordination bonds to the Cu(I) ion, with the third ligand a His from the ␣2 helix (Cys 36 Ј, His 61 , Cys 65 ), thus completing a trigonal S 2 N coordination complex (13).…”