Copper Binding Regulates Cellular Prion Protein Function

The cellular prion protein (PrP (c)), mainly known for its role in neurodegenerative diseases, is involved in several physiological processes including neuritogenesis. In addition, its ability to bind copper or zinc has been suggested for its role in metal homeostasis. Although PrP (c) has been known as a copper-binding molecule, little is known about how copper can affect PrP (c) physiological functions. By combining genomic approaches, cellular assays, and focal stimulation technique, we found that PrP (c) neuritogenesis function is directly influenced by N-terminal copper-binding amino acids. Several recombinant mouse PrP (recMoPrP) mutants at N-terminal copper-binding sites were produced, and primary hippocampal cultures were treated either in bulk or exposed near the hippocampal growth cones (GC) of single neurons in local stimulation manner. While focal stimulation of GC with wild-type recMoPrP induced neurite outgrowth and rapid GC turning toward the source, N-terminal mutants fail to support this effect. Indeed, disrupting all the copper-binding sites at the N-terminus of PrP (c) was toxic to neurons indicating that these regions are crucial for the protein function. Mutants at both octarepeat and non-octarepeat region abolished the neuritogenesis effect. Altogether, our findings indicate the crucial role of copper-binding sites in maintaining the neuritogenesis function in PrP, suggesting a potential link between loss-of-function of the protein and disease initiation.