Prions are the causative agents of a group of transmissible degenerative brain diseases that are fatal to humans and animals. The properties of the infectious agent and its mechanism of replication are unique. Prions are comprised of PrPSc, an abnormally folded, aggregated version of its host-encoded counterpart protein (PrPC); PrPSc self-replicates in the absence of informational nucleic acids by imposing its infectious conformation on PrPC. Our poor understanding of the structural properties of PrPSc represents an important knowledge gap in prion biology. This information is critical to elucidate the detailed mechanism of prion replication, the molecular basis of prion strain variation, and the factors controlling prion transmission between species. In this project, we focus on ascertaining the structural properties of prions causing chronic wasting disease (CWD), an uncontrollable, contagious epidemic of North American deer, elk, and other members of the cervid family, which is also emergent in Asian and European countries. The significant zoonotic potential and emergence of novel strains have established CWD as a significant public health concern. The specific objectives of our research are therefore (i) To determine structural properties of North American elk and deer CWD prions; (ii) To determine the effects of primary structural variation at prion protein residue 226 and route of transmission on CWD prion strain properties; and (iii) To determine the structural basis of strain variation in emerging Scandinavian CWD strains and an adapted derivative. Our proposed studies are truly interdisciplinary since they combine the complementary resources of two laboratories with expertise in novel mouse models for studying CWD, cell culture approaches, biochemical assays, and a host of state-of-the-art methods of structural biology. The later include several complementary mass spectrometry-based structural methods and cryo-electron microscopy, an emerging approach with high potential for providing long-sought insights into high-resolution structures of different prion strains.