title: Increasing prion propensity by hydrophobic insertion.
abstract: Prion formation involves the conversion of proteins from a soluble form into an infectious amyloid form. Most yeast prion proteins contain glutamine/asparagine-rich regions that are responsible for prion aggregation. Prion formation by these domains is driven primarily by amino acid composition, not primary sequence, yet there is a surprising disconnect between the amino acids thought to have the highest aggregation propensity and those that are actually found in yeast prion domains. Specifically, a recent mutagenic screen suggested that both aromatic and non-aromatic hydrophobic residues strongly promote prion formation. However, while aromatic residues are common in yeast prion domains, non-aromatic hydrophobic residues are strongly under-represented. Here, we directly test the effects of hydrophobic and aromatic residues on prion formation. Remarkably, we found that insertion of as few as two hydrophobic residues resulted in a multiple orders-of-magnitude increase in prion formation, and significant acceleration of in vitro amyloid formation. Thus, insertion or deletion of hydrophobic residues provides a simple tool to control the prion activity of a protein. These data, combined with bioinformatics analysis, suggest a limit on the number of strongly prion-promoting residues tolerated in glutamine/asparagine-rich domains. This limit may explain the under-representation of non-aromatic hydrophobic residues in yeast prion domains. Prion activity requires not only that a protein be able to form prion fibers, but also that these fibers be cleaved to generate new independently-segregating aggregates to offset dilution by cell division. Recent studies suggest that aromatic residues, but not non-aromatic hydrophobic residues, support the fiber cleavage step. Therefore, we propose that while both aromatic and non-aromatic hydrophobic residues promote prion formation, aromatic residues are favored in yeast prion domains because they serve a dual function, promoting both prion formation and chaperone-dependent prion propagation.
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Gonzalez Nelson
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Kacy R
authors.initials: KR
authors.lastname: Paul
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Michelina
authors.initials: M
authors.lastname: Petri
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Noe
authors.initials: N
authors.lastname: Flores
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Rogge
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Cascarina
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ross
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000378:metabolism*; D001216:Asparagine / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D019295:Computational Biology; D005973:Glutamine / Q000235:genetics / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation / Q000235:genetics; D011328:Prions / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
chemical_list: D000682:Amyloid; D011328:Prions; D029701:Saccharomyces cerevisiae Proteins; D005973:Glutamine; D014443:Tyrosine; D001216:Asparagine