The cellular form of the prion protein (PrP(C)) is found in both full-length and several different cleaved forms in vivo. Although the precise functions of the PrP(C) proteolytic products are not known, cleavage between the unstructured N-terminal domain and the structured C-terminal domain at Lys-109↓His-110 (mouse sequence), termed α-cleavage, has been shown to produce the anti-apoptotic N1 and the scrapie-resistant C1 peptide fragments. β-Cleavage, residing adjacent to the octarepeat domain and N-terminal to the α-cleavage site, is thought to arise from the action of reactive oxygen species produced from redox cycling of coordinated copper. We sought to elucidate the role of key members of the ADAM (a disintegrin and metalloproteinase) enzyme family, as well as Cu(2+) redox cycling, in recombinant mouse PrP (MoPrP) cleavage through LC/MS analysis. Our findings show that although Cu(2+) redox-generated reactive oxygen species do produce fragmentation corresponding to β-cleavage, ADAM8 also cleaves MoPrP in the octarepeat domain in a Cu(2+)- and Zn(2+)-dependent manner. Additional cleavage by ADAM8 was observed at the previously proposed location of α-cleavage, Lys-109↓His-110 (MoPrP sequencing); however, upon addition of Cu(2+), the location of α-cleavage shifted by several amino acids toward the C terminus. ADAM10 and ADAM17 have also been implicated in α-cleavage at Lys-109↓His-110; however, we observed that they instead cleaved MoPrP at a novel location, Ala-119↓Val-120, with additional cleavage by ADAM10 at Gly-227↓Arg-228 near the C terminus. Together, our results show that MoPrP cleavage is far more complex than previously thought and suggest a mechanism by which PrP(C) fragmentation responds to Cu(2+) and Zn(2+).
Keywords: ADAM; Alzheimer Disease; Copper; Enzyme; Metalloproteinase; Neurodegeneration; Prion Protein Proteolysis; Prions; Zinc.