Characterization of Prion Protein Conformational Changes

Transmissible spongiform encephalopathies (TSEs) are caused by a conformational change in the prion protein (PrP), which is a membrane-associated, glycoprotein. TSEs, or prion diseases, include Creutzfeldt-Jakob disease, fatal familial insomnia and Kuru in humans, scrapie in sheep, bovine spongiform encephalopathy in cattle, and chronic wasting disease in deer and elk. While rare, these diseases are always fatal.<P> Given that they are also transmissible, they don't necessarily just affect the afflicted patient or animal: the human forms represent a threat to blood and organ recipients and the animal forms are a threat to our food supply. The central hypothesis in prion disease is that it is a protein-only disease, whereby the prion protein is the only agent necessary for propagation and transmission.<P> In the disease process, the prion protein converts from its primarily helical, cellular form (PrPC) to a conformer rich in beta-structure with retention of most of the helical structure (PrPSc). PrPSc aggregates, causes disease, and is infectious. While most studies focus on just the protein, PrP's N-linked glycans influence PrP expression, distribution, and deposition in the brain, which in turn determines patient symptoms. Unfortunately it has proved impossible to obtain high-resolution structural information for the conversion process and corresponding disease-associated conformers from experiment. <P> Consequently, our hypothesis is that all-atom molecular dynamics simulations will provide testable models (to be tested in collaboration with Dr. Byron Caughey, NIH RML) for the conversion process, species barriers, the infectious oligomers, and the effect of glycosylation and the lipid membrane on the process. Specifically, we will: <ul><li> Perform multiple molecular dynamics (MD) simulations of the cellular prion protein (PrPC) from different species (human, bovine, hamster, ovine, mouse, chicken, turtle, pig and elk) in water at neutral and low pH (low pH triggers the conformational change to PrPSc both in vivo and in vitro) <LI> Perform MD simulations of more biologically relevant protein constructs by including glycans, the GPI anchor, and the membrane environment at neutral and low pH to assess their effect on conversion <LI> Construct molecular models for the infectious, toxic protofibrillar oligomers (not fibrils) of PrPSc and perform MD simulations of these constructs as well as hetero-oligomers (for example bovine PrPSc + human PrPC) to investigate species barriers.