Cu2+ binding triggers αBoPrP assembly into insoluble laminar polymers

Cu2+ binding is so far the best characterized property of the prion protein. This interaction has been mapped to the N-terminal domain of the prion protein where multiple His residues occur largely embedded within the repetitive PHGGGWGQ sequence known as octarepeats. When Cu2+ interaction is studied using a solution of full-length bovine prion protein containing six octarepeats at protein concentrations above 25 μM, a drastic increase in solution turbidity is observed due to the formation of insoluble cation–protein complexes that appear as bidimensional polymer meshes. These bidimensional meshes consist of a single layer of protein molecules crosslinked by Cu2+ cations. Polymer formation is a cooperative process that proceeds by nucleation of protein molecules with a Cu2+ site occupancy of above 2. These results support the hypothesis that the N-terminal domain of prion protein is a ligand binding module that promotes crosslinked assembly, and suggest the existence of inter-repeat Cu2+ sites. [Copyright &y& Elsevier]