Amyloid of the prion domain of Sup35p has an in-register parallel β-sheet structure

Abstract

The [ PSI + ] prion of Saccharomyces cerevisiae is a self-propagating amyloid form of Sup35p, a subunit of the translation termination factor. Using solid-state NMR we have examined the structure of amyloid fibrils formed in vitro from purified recombinant Sup35 1–253 , consisting of the glutamine- and asparagine-rich N-terminal 123-residue prion domain (N) and the adjacent 130-residue highly charged M domain. Measurements of magnetic dipole–dipole couplings among 13 C nuclei in a series of Sup35NM fibril samples, 13 C-labeled at backbone carbonyl sites of Tyr, Leu, or Phe residues or at side-chain methyl sites of Ala residues, indicate intermolecular 13 C– 13 C distances of ≈0.5 nm for nearly all sites in the N domain. Certain sites in the M domain also exhibit intermolecular distances of ≈0.5 nm. These results indicate that an in-register parallel β-sheet structure underlies the [ PSI + ] prion phenomenon.