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The Application of 199 Hg NMR and 199m Hg Perturbed Angular Correlation (PAC) Spectroscopy to Define the Biological Chemistry of Hg II : A Case Study with Designed Two- and Three-Stranded Coiled Coils

Chemistry - A European Journal
Wiley Blackwell (John Wiley & Sons)
Publication Date
  • Biology
  • Chemistry
  • Design


The use of de novo designed peptides is a powerful strategy to elucidate Hg II –protein interactions and to gain insight into the chemistry of Hg II in biological systems. Cysteine derivatives of the designed Α-helical peptides of the TRI family [Ac-G-(L a K b A c L d E e E f K g ) 4 -G-NH 2 ] bind Hg II at high pH values and at peptide/Hg II ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting Hg II complexes are good water-soluble models for Hg II binding to the protein MerR. We have carried out a parallel study using 199 Hg NMR and 199m Hg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI 14L9C/Hg II ratios. These studies prove for the first time the formation of [Hg{(TRI 14L9C) 2 -(TRI 14L9C[bond]H)}], a dithiolate–Hg II complex in the hydrophobic interior of the three-stranded coiled coil (TRI 14L9C) 3 . 199 Hg NMR and 199m Hg PAC data demonstrate that this dithiolate–Hg II complex is different from the dithiolate [Hg(TRI 14L9C) 2 ], and that the presence of third Α-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI 14L9C) 2 ]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate–Hg II complex Hg(TRI 14L9C) 3 − on a timescale that is slower than the NMR timescale (0.01–10 14ms). The formation of the species [Hg{(TRI 14L9C) 2 (TRI 14L9C[bond]H)}] is the result of a compromise between the high affinity of Hg II to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil.

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