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Circular dichroism (CD) spectroscopy in the visible region (vis‐CD) is a powerful technique to study metal–protein interactions. It can resolve individual d–d electronic transitions as separate bands and is particularly sensitive to the chiral environment of the transition metals. Modern quantum chemical methods enable CD spectra calculations from which, along with direct comparison with the experimental CD data, the conformations and the stereochemistry of the metal–protein complexes can be assigned. However, a clear understanding of the observed spectra and the molecular configuration is largely lacking. In this study, we compare the experimental and computed vis‐CD spectra of Cu2+‐loaded model peptides in square‐planar complexes. We find that the spectra can readily discriminate the coordination pattern of Cu2+ bound exclusively to main‐chain amides from that involving both main‐chain amides and a side‐chain (i.e. histidine side‐chain). Based on the results, we develop a set of empirical rules that relates the appearance of particular vis‐CD spectral features to the conformation of the complex. These rules can be used to gain insight into coordination geometries of other Cu2+–or Ni2+–protein complexes.

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While it has been reported that wild type Amyloid β (1–42) aggregates are highly toxic, we demonstrate that addition of a discrete macrocyclic host molecule, cucurbit[8]uril, increases the aggregation rate of the peptide but substantially reduces its toxicity.

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.

Alpha-synuclein (αSyn) forms amyloid fibrils in the neurons of Parkinson's disease (PD) patients'. Despite a role for Cu 2+ in accelerating αSyn fibril formation, coupled with reports of copper dishomeostasis in Parkinson's disease (PD), there remain controversies surrounding the coordination geometry of Cu 2+ with αSyn. Here we compare visible circular dichroism (CD) spectra of Cu 2+ loaded on to full-length αSyn together with four peptides that model aspects of Cu 2+ binding to the N-terminus and Histidine50 of αSyn. Using glycine as a competitive ligand, the affinity of Cu 2+ for full-length αSyn is determined to have a conditional dissociation constant, at pH 7.4, of 0.1 nM. A similar affinity of 0.3 nM is determined for the tri-peptide MDV that mimics the N-terminus of αSyn, while the incorporation of a putative histidine side-chain in the Nterminal complex facilitates the formation of a macrochelate with the histidine, which results in an increase in

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