"Biological Ice-nine: Resolving the Structural Conversion, Aggregation and Neurotoxicity of Prion Proteins at the Single Molecule Level "

Sanjeevi Sivasankar, Ph.D.
Associate Professor
Department of Physics & Astronomy
Iowa State University

In Kurt Vonnegut’s Cat’s Cradle, the physicist Felix Hoenikker creates ice-nine, a highly stable form of crystalline water that seeds its own replication and instantly freezes any liquid water it touches. Vonnegut’s fictitious ice-nine has a very real biological counterpart: the prion protein. When a prion protein misfolds, it imposes its structure upon natively folded proteins and templates their aggregation. The consequence of this self-amplifying cycle is an accumulation of toxic prion protein aggregates that destroys neurons and invariably kill the organism. Copper exposure has been linked to the formation of pathogenic prion aggregates, however, the mechanism of its action is unknown. Here, we use quantitative biophysical measurements and system level assays to establish a direct link, at the molecular level, between copper exposure and prion pathology. Using fluorescence and force based single molecule assays, we demonstrate that copper induces prion protein monomers to misfold into a high-affinity conformation before assembling into oligomers; the flexible tail of the protein is obligatory in this process. Using a cell-free seeding assay, we show that misfolded proteins serve as seeds that impose their structures upon native prion proteins and template their aggregation. Finally, using brain slice cultures, we demonstrate that the copper induced oligomers mediate inflammation and degeneration of neuronal tissue.