Copper(II) Binding Modes in the Prion Octapeptide PHGGGWGQ: A Spectroscopic and Voltammetric Study
✍ Scribed by Raffaele P. Bonomo; Giuseppe Impellizzeri; Giuseppe Pappalardo; Enrico Rizzarelli; Giovanni Tabbì
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 154 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
The N-terminal octapeptide repeat region of human prion protein (PrP c ) is known to bind Cu II . To investigate the binding modes of copper in PrP c , an octapeptide Ac-PHGGGWGQ-NH 2 (1), which corresponds to an octarepeat sequence, and a tetrapeptide Ac-HGGG-NH 2 (2) have been synthesised. The copper(ii) complexes formed with 1 and 2 have been studied by circular dichroism (CD) and electron spin resonance (ESR) spectroscopy. Both peptides form 1:1 complexes with Cu II at neutral and basic pH. CD, ESR and visible absorption spectra suggest a similar co-ordination sphere of the metal ion in both peptides, which at neutral pH consists of a square pyramidal geometry with three peptidic nitrogens and the imidazole nitrogen as donor atoms. Cyclic voltammetric measurements were used to confirm the geometrical features of these copper(ii) complexes: the observation of negative redox potentials are in good agreement with the inferred geometry. All these results taken together suggest that peptide 1 provides a single metal binding site to which copper(ii) binds strongly at neutral and basic pH and that the binding of the metal induces the formation of a stiffened structure in the HGGG peptide fragment.