Abstract
Intracellular CuI is controlled by the transcriptional regulator CueR, which effectively discriminates between monovalent and divalent metal ions. It is intriguing that HgII does not activate transcription, as bis‐thiolate metal sites exhibit high affinity for HgII. Here the binding of HgII to CueR and a truncated variant, ΔC7‐CueR, without the last 7 amino acids at the C‐terminus including a conserved CCHH motif is explored. ESI‐MS demonstrates that up to two HgII bind to CueR, while ΔC7‐CueR accommodates only one HgII. 199mHg PAC and UV absorption spectroscopy indicate HgS2 structure at both the functional and the CCHH metal site. However, at sub‐equimolar concentrations of HgII at pH 8.0, the metal binding site displays an equilibrium between HgS2 and HgS3, involving cysteines from both sites. We hypothesize that the C‐terminal CCHH motif provides auxiliary ligands that coordinate to HgII and thereby prevents activation of transcription.
Highlights
CueR proteins from various bacteria contain two additional well conserved cysteines at the C-terminal, disordered segment of the protein (Figure 1).[2]
The repressor forms of the DNA-bound CueR dimer suggest that a two-turn helix between the metal binding loop and the CCHH motif may have a key role in the protein function.[5]
With the present work we aim to explore the role of the Cterminal CCHH motif with a particular focus on the binding of HgII to CueR
Summary
CueR proteins from various bacteria contain two additional well conserved cysteines at the C-terminal, disordered segment of the protein (Figure 1).[2]. For the experiment with 2.0 equivalents of HgII the signal may be satisfactorily fitted with just one (high frequency) NQI, presumably reflecting HgS2 structure for both HgII bound to CueR (Figure 3).
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