Tying Up a Loose End: On the Role of the C‐Terminal CCHHRAG Fragment of the Metalloregulator CueR

Abstract

The transcriptional regulator CueR is activated by the binding of Cu I , Ag I , or Au I to two cysteinates in a near-linear fashion. The C-terminal CCHHRAG sequence in Escherichia coli CueR present potential additional metal binding ligands and here we explore the effect of deleting this fragment on the binding of Ag I to CueR. CD spectroscopic and ESI-MS data indicate that the high Ag I -binding affinity of WT-CueR is significantly reduced in Δ7C-CueR. [111 Ag PAC spectroscopy demonstrates that the WT-CueR metal site structure (AgS 2 ) is conserved, but less populated in the truncated variant. Thus, the function of the Cterminal fragment may be to stabilize the two-coordinate metal site for cognate monovalent metal ions. In a broader perspective this is an example of residues beyond the second coordination sphere affecting metal site physicochemical properties while leaving the structure unperturbed.

Inducing α‐Helicity in Peptides by Silver Coordination to Cysteine

“…The authors have cited additional references within the Supporting Information. [30][31][32][33][34][35][36][37][38]…”

“…Detailed experimental procedures, compound data, circular dichroism spectra, analysis of pH‐potentiometric data, HPLC chromatograms, LCMS data and NMR spectra are provided in the Supporting Information. The authors have cited additional references within the Supporting Information [30–38] …”

Probing the Bioinorganic Chemistry of Cu(I) with 111Ag Perturbed Angular Correlation (PAC) Spectroscopy

“…Ser77 from the other monomer of the protein dimer is positioned close to the metal site. 111 Ag PAC was applied to characterize the CueR metal binding site [32,33], see Figure 7, and the decay of 111 Ag to 111 Cd(II) provided a means to elucidate the effect of instantaneously changing from Ag(I), which activates the protein function, to Cd(II), which does not. Contrary to the rigid small blue copper proteins, vide supra, significant structural changes are induced at the CueR metal site by the Ag(I) to Cd(II) transition.…”

“…One of the signals is in good agreement with an almost linear structure with two coordinating thiolates, as expected, possibly with a weak ligand in the equatorial plane, such as carbonyl oxygen, suggested to be from Ser77 (high frequency signal, top panel, Figure 7). The other signal indicated a higher coordination number, thus im- 111 Ag PAC was applied to characterize the CueR metal binding site [32,33], see Figure 7, and the decay of 111 Ag to 111 Cd(II) provided a means to elucidate the effect of instantaneously changing from Ag(I), which activates the protein function, to Cd(II), which does not. Contrary to the rigid small blue copper proteins, vide supra, significant structural changes are induced at the CueR metal site by the Ag(I) to Cd(II) transition.…”

“…With this work, we review applications of 111 Ag PAC spectroscopy within Cu(I) bioinorganic chemistry, which so far only encompasses electron transfer proteins (plastocyanin and azurin) [26][27][28][29], an oxygen transport protein (hemocyanin) [30], and metal-ionsensing proteins functioning as transcriptional regulators (CueR and BxmR) [31][32][33].…”