Copper Binding to the N-Terminal Tandem Repeat Region of Mammalian and Avian Prion Protein: Structural Studies Using Synthetic Peptides

Using CD spectroscopy we have investigated the effect of Cu 2+ on the secondary structure of synthetic peptides Octa 4 and Hexa 4 corresponding to tetra-repeats of the octapeptide of mammalian PrP and the hexapeptide of chicken PrP. In addition, fluorescence spectroscopy was used to estimate the dissociation constants (Kd), of Cu 2+ binding by both peptides. Both peptides exhibited unusual CD spectra, complicated by the high proportion of aromatic residues, revealing little secondary structure in aqueous solution. Addition of Cu 2+ to Hexa 4 induced an increase in random coil to resemble Octa 4. The fluorescence of both peptides was quenched by Cu 2+ and this was used to calculate Kd′s of 6.7 μM for Octa 4 and 4.5 μM for Hexa 4. Other divalent cations showed lesser effects on the fluorescence of the peptides.