20.109 (S10) W/F Green Group's Research Proposal

Research Problem and Goal

Prions are infectious proteins that are abnormally folded into an extremely stable conformation. Instead of propagating through DNA replication, they induce normal proteins to take on the misfolded structure, resulting in protein aggregates that lead to untreatable, devastating neurodegenerative conditions such as Creutzfeldt-Jakob disease (CJD) and mad cow disease. Similarities between the amyloid plaques of prion disease and those of Alzheimer’s disease suggest that prions may even play a role in more common degenerative disorders. In addition to being highly transmissible, their structural stability causes prions to be extremely difficult to eradicate, posing many challenges in finding a cure for prion diseases. Although a suggested cure involves altogether eliminating the naturally-occuring prion protein PrPC, thus preventing its shift to the diseased protein PrPSC, recent findings indicate that normal prions are critical for neuron health.
We believe that a more viable, less dangerous cure would involve inhibiting the pathogenic conversion process. This can be achieved through various approaches, including greater stabilization of the PrPC conformation, inhibition of the PrPC-PrPSC interaction, or inhibition of the pathogenic conformational shift. We plan to use protein engineering and/or RNA engineering to design biological molecules that can be used to achieve one or more of the above goals. We hope that our findings will provide greater insight into the mechanisms of prion activity, and contribute to the development of safe, effective anti-prion treatments.

Background Information and Previous Work

Bremer J, Baumann F, Tiberi C, et al. Axonal prion protein is required for peripheral myelin maintenance. Nature Neuroscience 2010; 13:310-318.

• Researchers have long wondered what the function of normal prion protein was; this study indicates that normal PrPC protein is involved in maintaining the myelin sheath of neurons. In the study, the gene for PrPC was knocked out in four strains of mice. At birth, the mice were all healthy, but within six weeks extensive myelin damage was observed. This chronic demyelinating polyneuropathy (CDP) was found when PrPC was knocked out in neurons, and suppressed when PrPC was expressed. These findings show that prevention of prion disease through ablation of normal prion protein would cause extensive damage to the nervous system, and is likely not a viable cure.

Villegas V, Zurdo J, Filimonov VV, et al. Protein engineering as a strategy to avoid formation of amyloid fibrils. Protein Science 2000; 9(9): 1700-1708.

• Aggregated molecules of human procarboxypeptidase A2 (ADA2h) protein show well-defined, stable structures that are characteristic of fibrils formed in amylodoitic diseases. It has been found that mutant ADA2h proteins that show increased stability of local helical domains are less likely to aggregate and from fibrils. This is possibly because the increased stability favors local interactions over the long-range ones needed for aggregation. These findings suggest the possibility of using protein engineering to lower the potential of a protein to form fibrils, without significantly interfering with its structure or its function.