Two Prion Variants of Sup35p Have In-Register Parallel β-Sheet Structures, Independent of Hydration

The [PSI+] prion is a self-propagating amyloid of the Sup35 protein, normally a subunit of the translation termination factor, but impaired in this vital function when in the amyloid form. The Sup35 N, M, and C domains are the amino-terminal prion domain, a connecting polar domain, and the essential C-terminal domain resembling eukaryotic elongation factor 1 alpha respectively. Different [PSI+] isolates (prion variants) may have distinct biological properties, associated with different amyloid structures. Here we use solid state NMR to examine the structure of infectious Sup35NM amyloid fibrils of two prion variants. We find that both variants have an in-register parallel beta-sheet structure, both in the fully hydrated form and in the lyophilized form. Moreover, we confirm that some leucine residues in the M domain participate in the in-register parallel P-sheet structure. Transmission of the [PSI+] prion by amyloid fibrils of Sup35NM and transmission of the [URE3] prion by amyloid fibrils of recombinant full-length Ure2p are similar whether they have been lyophilized or not (wet or dry).