Ordering the Pathway of Prion Propagation in Yeast Through a Structure/Function Analysis of Hsp104 (Paperback)

In these studies, I investigate the role of Hsp104 in the Saccharomyces cerevisiae prion propagation pathway by an in vivo analysis using synthetic Hsp104 chimera constructs, by mutagenesis of the potentially substrate-recognizing N-terminal domain (NTD) and by extract-based assays of Hsp104 activity. The yeast prion PSI]] is an amyloid-based aggregate of the translation termination factor Sup35 and is strictly reliant upon the Clp/Hsp100 AAA+ ATPase Hsp104 for its maintenance in a dividing cell population. Early extract experiments indicated Hsp104 activity on Sup35 fibers is a severing reaction that results in the production of fiber fragments. Through my synthetic biology experiments, I find that this Hsp104 yeast prion propagation reaction depends upon an initial step mediated by the Hsp40 Sis1, and by extension the Hsp70 Ssa1/2, and proceeds by translocation of prion proteins from aggregated substrates through the central channel of Hsp104. My data indicate there is no necessary downstream coupling of Hsp104 to other yeast chaperone systems for its function in prion propagation. Finally, I identify the mutation R59A in the NTD, which has no effect on amorphous aggregates and has differing effects on distinct conformations of PSI]] aggregates. From these findings, I extend my model of prion propagation to include the NTD as an important substrate-selective gate and processivity factor for Hsp104 function.