Domain Analysis of Arabidopsis Thaliana Sis1 Orthologs in Yeast Prion Propagation

Protein misfolding is associated with many common neurological diseases such as Alzheimer’s disease and Parkinson’s disease. A hallmark of these neurodegenerative diseases is protein aggregation in the form of amyloids. Amyloids are also the structural basis of at least some prions. Amyloid‐based prions are infectious, self‐propagating protein conformers that cause normally‐folded protein to adopt a similar misfolded conformation and aggregate to form amyloid. This amyloid‐based prion propagation is observed in the baker’s yeast Saccharomyces cerevisiae . In S. cerevisiae , chaperone proteins are also involved in the propagation of prions within cell populations. One such chaperone, the J‐protein Sis1, is required for propagating all amyloid‐based yeast prions, including the prions [ PSI + ] and [ RNQ + ]. Sis1 is a multi‐domain protein and numerous experiments have shown domain‐specific requirements for the propagation of distinct prions. We previously identified six functional orthologs of Sis1 in the model plant Arabidopsis thaliana and showed that these six paralogous proteins differ in their ability to maintain distinct prions when complementing a deletion of SIS1 in yeast; however, the combination of domains needed to propagate each prion is unknown. Therefore, this study focuses on testing the individual prion‐propagating properties of various A. thaliana Sis1 constructs to elucidate the domain combinations of each ortholog necessary to propagate specific prions using biochemical assays and yeast plasmid shuffling. Preliminary results indicate the primacy of the glycine‐rich region of the Sis1 protein. Additionally they indicate that, although naturally occurring as dimers, these proteins may function as well or better as monomers in prion propagation, consistent with previous work on Sis1 itself. The long‐term goal of the investigation is to decipher specific structural characteristics, and amino acid sequences, that give rise to prion‐specific propagating functions in chaperone proteins.