A complete catalog of wild-type Sup35 prion variants and their protein-only propagation

Twenty-three prion variants of the wild-type Sup35 protein are obtained, including 19 novel ones and 4 previously documented, namely, VH, VK, VL, and W8. Their uniqueness and non-composite nature are demonstrated. Specific infectivity is generated de novo for most variants by adding prion particles to solutions of a purified Sup35 N-terminal fragment, thereby supporting the protein-only composition. Sup35 prions isolated by other laboratories are identified within the collection and found to fall into a narrow set of five variant types that are readily inducible in vivo by Sup35 overexpression. The work establishes an unambiguous and extensive collection of prion variants, demonstrating that a protein, by itself, in the absence of genetic and conformational co-factors, could adopt a great number of structures. In light of recent high-resolution structures of other amyloids, we discuss how the diverse folding is achieved in spite of apparent contradiction to the classical paradigm that a protein's structure is uniquely determined by its sequence.