Importance of low-oligomeric-weight species for prion propagation in the yeast prion system Sup35/Hsp104

Publisher Website
Google Scholar
Abstract
The [PSI+] determinant of Saccharomyces cerevisiae, consisting of the cytosolic translation termination factor Sup35, is a prion-type genetic element that induces an inheritable conformational change and converts the Sup35 protein into amyloid fibers. The molecular chaperone Hsp104 is required to maintain self-replication of [PSI+]. We observe in vitro that addition of catalytic amounts of Hsp104 to the prion-determining region of the NM domain of Sup35, Sup355–26, results in the dissociation of oligomeric Sup35 into monomeric species. Several intermediates of Sup355–26 could be detected during this process. Strong interactions are found between Hsp104 and hexameric/tetrameric Sup355–26, whereas the intermediate and monomeric “release” forms show a decreased affinity with respect to Hsp104, as monitored by saturation transfer difference and diffusion-ordered NMR spectroscopic experiments. Interactions are mediated mostly by the side chains of Gln, Asn, and Tyr residues in Sup355–26. No interaction can be detected between Hsp104 and higher oligomeric states (≥8) of Sup355–26. Taking into account the fact that Hsp104 is required for maintenance of [PSI+], we suggest that low-oligomeric-weight species of Sup35 are important for prion propagation in yeast.