Structure of an infectious mammalian prion

Classical mammalian prions are assemblies of prion protein molecules that are extraordinarily transmissible, with a microgram of protein containing up to 10⁸lethal doses of infectivity^1,2. Unlike most other pathologic and amyloidogenic proteins, prions typically contain glycolipid anchors³and abundant asparagine‐linked glycans^4‐6. The infectious nature, complexity, and biophysical properties of prions have complicated structural analyses and stymied any prior elucidation of 3D conformation at the polypeptide backbone level⁷. Here we have determined the structure of the core of a fully infectious, brain‐derived prion by cryo‐electron microscopy with ∼3.1 Å resolution. The purified prions are amyloid fibrils comprised of monomers assembled with parallel in‐register intermolecular beta sheets and connecting chains. Residues ∼95‐227 of each monomer provide one rung of the ordered fibril core, with the glycans and glycolipid anchor projecting from the lateral surfaces of the fibril. The fibril ends, where prion growth occurs, are formed by single monomers in an extended serpentine combination of β‐ arches, a Greek key, and loops that presumably template the refolding of incoming monomers. Our results describe an atomic model to underpin detailed molecular hypotheses of how pathologic prion proteins can propagate as infectious agents, and how such propagation and associated pathogenesis might be impeded.