Novel Glutaredoxin Activity of the Yeast Prion Protein Ure2 Reveals a Native-like Dimer within Fibrils

Abstract

Ure2 is the protein determinant of the Saccharomyces cerevisiae prion [URE3]. Ure2 has structural similarity to glutathione transferases, protects cells against heavy metal and oxidant toxicity in vivo, and shows glutathione-dependent peroxidase activity in vitro. Here we report that Ure2 (which has no cysteine residues) also shows thiol-disulfide oxidoreductase activity similar to that of glutaredoxin enzymes. This demonstrates that disulfide reductase activity can be independent of the classical glutaredoxin CXXC/CXXS motif or indeed an intrinsic catalytic cysteine residue. The kinetics of the glutaredoxin activity of Ure2 showed positive cooperativity for the substrate glutathione in both the soluble native state and in amyloid-like fibrils, indicating native-like dimeric structure within Ure2 fibrils. Characterization of the glutaredoxin activity of Ure2 sheds light on its ability to protect yeast from heavy metal ion and oxidant toxicity and suggests a role in reversible protein glutathionylation signal transduction. Observation of allosteric enzyme behavior within amyloid-like Ure2 fibrils not only provides insight into the molecular structure of the fibrils but also has implications for the mechanism of [URE3] prion formation.

The fungal glutathione S-transferase system. Evidence of new classes in the wood-degrading basidiomycete Phanerochaete chrysosporium

“…The authors thus suggest that mutations have allowed URE2p to diversify and acquire additional functions as a prion and a repressor of nitrogen catabolism. It has been recently shown that ScUREp also shows thiol-disulfide oxidoreductase activity similar to that of glutaredoxins even if it does not possess cysteine residue [50]. Concerning the investigated fungi of our study, only C. albicans and S. cerevisiae exhibit the N-terminal prion domain; however, many other fungal sequences with shorter URE2p and deprived of the prion domain cluster are present in this class (Fig.…”

Functional Divergence of the Glutathione S-Transferase Supergene Family in Physcomitrella patens Reveals Complex Patterns of Large Gene Family Evolution in Land Plants

“…S7A). Fungal and bacterial Ure2p proteins were known to be active as dimers (Wadington et al, 2009;Zhang and Perrett, 2009). Fungal Ure2p proteins did not show detectable GST activity toward the standard substrate CDNB, but they had GSH-dependent peroxidase activity (Zhang et al, 2008).…”

Prions in Yeast

“…Indeed, non-prion domains have been shown to retain their structure and activity even within the prion aggregate (Baxa et al 2002Bai et al 2004;Krzewska et al 2007;Zhang et al 2008;Zhang and Perrett 2009). More importantly, amyloid fibers of PrD fragments are infectious when transfected into non-prioncontaining cells (King and Diaz-Avalos 2004;Tanaka et al 2004;Brachmann et al 2005;Diaz-Avalos et al 2005;Patel and Liebman 2007;Du et al 2008Du et al , 2010Alberti et al 2009).…”