Copper(II) sequentially loads onto the N-terminal amino group of the cellular prion protein before the individual octarepeats.

Abstract

The cellular prion protein (PrPC) binds to Cu2+ ions in vivo, and a misfolded form of PrPC is responsible for a range of transmissible spongiform encephalopathies. Recently, disruption of Cu2+ homeostasis in mice has been shown to impart resistance to scrapie infection. Using full-length PrPC and model peptide fragments, we monitor the sequential loading of Cu2+ ions onto PrPC using visible circular dichroism. We show the N-terminal amino group of PrPC is not the principal binding site for Cu2+; however, surprisingly, it has an affinity for Cu2+ tighter than that of the individual octarepeat binding sites present within PrPC. We re-evaluate what is understood about the sequential loading of Cu2+ onto the full-length protein and show for the first time that Cu2+ loads onto the N-terminal amino group before the single octarepeat binding sites.