Figure 2. Spectroscopic studies of the peptides corresponding to the human and Xenopus Zn knuckles (pep-hZnK and pep-xZnK).

(A) The CD spectra of the two peptides are characteristic of unfolded proteins (black and yellow, respectively). The addition of Zn²⁺ in equimolar amount, triggers the formation of secondary structures for the Xenopus peptide but not for the human one. (B) Left: 1D ¹H NMR spectra of pep-hZnK in absence (black) and presence (blue) of Zn²⁺. Right: 1D ¹H NMR spectra of pep-xZnK in absence (black) and presence (pink) of Zn²⁺. (C) Left: NMR bundle of the best 15 structures for the Xenopus Zn knuckle peptide (pep-xZnK). Right: Cartoon representation of one representative NMR structure. The Zn²⁺ metal ion is in purple and residues involved in Zn²⁺ coordination are depicted as ball-and-sticks.