Influence of Hydroxylation and Copper Binding on Poly (L‐Proline) Type II Helix Formation in the N‐terminal Domain of the Prion Protein

Abstract

A family of neurodegenerative disorders including scrapie, chronic wasting disease, bovine spongiform encephalopathy and Creutzfeldt‐Jakob disease are thought to be associated with the conversion of normal cellular prion protein (PrPc) to a protease resistant prion isoform, PrPSc (prion protein scrapie). The N‐terminal region of PrP is highly flexible, containing poly (L‐proline) type II (PPII) helical content. The five octarepeat sequences in the N‐terminal region of the prion protein (amino acids 53–90) are also involved in metal ion binding. While the biological role of the N‐terminal region in the conversion of PrPc to PrPSc remains unclear, a recent report indicates that Pro 44 is post‐translationally modified to a 4‐hydroxyproline residue (4‐Hyp) and that the PPII helix content is increased in N‐terminal domain peptides that are hydroxylated. Circular dichroism spectroscopy has been used to examine the effect of hydroxylation at Pro 44 on PPII helix formation in unmodified and modified (4‐Hyp) model peptides of the N‐terminal domain containing zero, one, or two octarepeat sequences (amino acids 37–53, 37–61, 37–69). In all cases, hydroxylation of Pro 44 increases PPII helical content. The addition of copper to these peptides also alters PPII helical content, with different effects observed for each pair of peptides.