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.

Developing predictive rules for coordination geometry from visible circular dichroism of copper(II) and nickel(II) ions in histidine and amide main‐chain complexes

“…Hence, the nature of the first residue affects the His conformation, which affects the chirality of the complexes. This in turn determines the vis‐CD spectral pattern observed experimentally both in the peptide models and, for example, in the His96 and His111 sites of PrP and other histidine‐containing peptides .…”

“…a whole series of pentapeptides, eight in all, related to PrP(92–96) and PrP(107–111) . Furthermore, the Cu 2+ Ac‐GGGH and Ac‐GGHG visible CD spectra have the appearance of Ac‐GGH. Additionally, Cu 2+ and Ni 2+ square‐planar four nitrogen complexes of Ac‐ELAKHA and Ac‐TESHAK peptides , models of the C‐terminal tail of histone H2A, have the inverted appearance of Ac‐AAH, as predicted.…”

“…8A). Cu 2+ binding to the N-terminal amino group of PrP C shows this type of spectrum [24], while Cu 2+ binding to the N-terminal amino group of a-synuclein does not because of the additional coordination of an Asp side-chain [9].…”

Interaction between Prion Protein's Copper-Bound Octarepeat Domain and a Charged C-Terminal Pocket Suggests a Mechanism for N-Terminal Regulation

“…These sites, variably referred to as the 5 th site or non-OR sites, can each bind a single Cu 2+ ion with nanomolar to sub-nanomolar affinity, placing them roughly equal in affinity to the tightest binding OR mode (component 3) (Nadal et al, 2009; Walter et al, 2009). Finally, the extreme N-terminus of PrP is capable of binding Cu 2+ through the terminal amino group with a dissociation constant that is roughly equivalent to the single-His (component 1) OR binding mode (Stanyon et al, 2014; Whittal et al, 2008). In total, full-length PrP can bind up to seven equivalents of copper per protein molecule at physiological pH: four in the OR, two in the non-OR sites, and one at the extreme N-terminus.…”

Truncated Amyloid-β(11–40/42) from Alzheimer Disease Binds Cu2+ with a Femtomolar Affinity and Influences Fiber Assembly

“…When bound to proteins and peptides Cu 2ϩ can produce very characteristic visible CD bands (54,55). Cu 2ϩ -derived visible CD bands arise from amide-main chain coordination being in close proximity to the chiral center, fixed in a chelate ring (56,57).…”