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 Cu2+ 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 Cu2+ 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 Cu2+ to Hexa(4) induced an increase in random coil to resemble Octa(4). The fluorescence of both peptides was quenched by Cu2+ and this was used to calculate Kd's of 6.7 mu M for Octa(4) and 4.5 mu M for Hexa(4). Other divalent cations showed lesser effects on the fluorescence of the peptides. (C) 1995 Academic Press, Inc.