Towards the role of metal ions in the structural variability of proteins: CdII speciation of a metal ion binding loop motif

Abstract

A de novo designed dodecapeptide (HS), inspired by the metal binding loops of metal-responsive transcriptional activators, was synthesized. The aim was to create a model system for structurally promiscuous and intrinsically unstructured proteins, and explore the effect of metal ions on their structure and dynamics. The interaction with Cd(II) was investigated by UV, synchrotron radiation CD, (1)H NMR, and perturbed angular correlation (PAC) of γ-rays spectroscopy, pH-potentiometry, and molecular modelling. The peptide mainly displays characteristics of random coil in the CD spectra, and the molecular dynamics simulations demonstrate that it is unstructured with transient and varying helical content. The spectroscopic studies revealed the formation of loop structures with the coordination of the two Cys-thiolates close to each end of the HS peptide, in the presence of one equivalent of Cd(II) per ligand. The imidazole moiety from histidine is also bound to Cd(II) at neutral pH and above. In the presence of 0.5 equivalent of Cd(II) per HS metal bridged structures with e.g. CdS(2)N(2) and possibly CdS(4) coordination geometries are formed above pH ~6. In an equilibrium of several co-existing species the peptide is exchanging between a number of structures also in its metal ion bound state(s), as indicated by NMR and PAC data.

Competition of zinc(II) with cadmium(II) or mercury(II) in binding to a 12-mer peptide

“…The ligand (Scheme 1) contains two cysteine residues as the most potent binding sites for d 10 metal ions close to the termini of the molecule..In order to increase the flexibility of the ligand one of the two proline units of the native sequence was replaced by a serine residue that is, indeed, present in a number of other MerR family member proteins [31] being sensitive for divalent metal ions. The metal-bound peptide may form a loop structure, as shown previously for the cadmium(II)-complexes of a related ligand [32]. It may be asked, however, whether zinc(II) and cadmium(II) or mercury(II) form similarly stable and structurally analogous complexes with the dodecapeptide.…”

“…The investigated peptide N-acetyl-Ser-Cys-Pro-Gly-Asp-Gln-Gly-Ser-Asp-Cys-Ser-Ile-NH 2 (Ac-SCPGDQGSDCSI-NH 2 , PS) was prepared by solid phase peptide synthesis using the Fmoc methodology (Fmoc = 9-fluorenylmethoxycarbonyl) and purified by reversed-phase HPLC, as described for a related ligand [32]. All other chemicals and solvents were obtained from Sigma-Aldrich and used without further purification unless otherwise described.…”

Cd(II) Capture Ability of an Immobilized, Fluorescent Hexapeptide

“…Data could be well fitted by considering four consecutive deprotonation steps corresponding to dissociation of the two cysteine sidechain thiol and two tyrosine sidechain phenol groups. The determined pK a values (shown in Table 1) fall in the range characteristic to Cys 33,51 and Tyr residues 55,56 within a peptide chain.…”

“…The metal-ion binding features of several short oligopeptides, containing two cysteine residues, have already been investigated in our group from different perspectives. 33,34 The studied 12-mer oligopeptide ligands proved to coordinate the studied group-12 metal ions (Zn(II), Cd(II) and Hg(II)) rather efficiently. Reports discussing the heavy metal ion binding capabilities of similar compounds, such as cysteine and poly-L-cysteine, 35,36 as well as poly-L-aspartate, 37 coupled to various solid supports (e.g.…”

Metalloproteinek fémkötőhelyein alapuló oligopeptidek, mint potenciális toxikus fémion érzékelők

“…28 The major result of our studies on the various metal ionoligopeptide systems is a finding that the model ligands possess fundamentally distinct binding features for the monovalent ion Ag + and the divalent ions Zn 2+ , Cd 2+ and Hg 2+ . [29][30][31][32] The binding of Ag + to the ligands under acidic conditions (even at pH = 2) was proved by UV-, CD-and 1 H-NMR experiments, as well as pH-potentiometric titrations ( Figure 6). 31 Spectroscopic data suggest the coordination of at least one of the Cys-sidechain donors as a thiolate to Ag + in the Ag + -PP 1:1 system (PP = Ac-SCPGDQGSDCPI-NH 2 ).…”