Originally published as Genetics Published Articles Ahead of Print on April 2, 2006.

Genetics, Vol. 173, 611-620, June 2006, Copyright © 2006
doi:10.1534/genetics.106.056820

N-Terminal Domain of Yeast Hsp104 Chaperone Is Dispensable for Thermotolerance and Prion Propagation but Necessary for Curing Prions by Hsp104 Overexpression

Guo-Chiuan Hung and Daniel C. Masison¹

Laboratory of Biochemistry and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0851

¹ Corresponding author: Building 8, Room 407, Laboratory of Biochemistry and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, 8 Center Dr., Bethesda, MD 20892-0851.
E-mail: masisond{at}helix.nih.gov

Hsp104 is a hexameric protein chaperone that resolubilizes stress-damaged proteins from aggregates. Hsp104 promotes [PSI⁺] prion propagation by breaking prion aggregates, which propagate as amyloid fibers, into more numerous prion "seeds." Inactivating Hsp104 cures cells of [PSI⁺] and other amyloid-like yeast prions. Overexpressing Hsp104 also eliminates [PSI⁺], presumably by completely resolubilizing prion aggregates. Inexplicably, however, excess Hsp104 does not cure the other prions. Here we identify missense mutations in Hsp104's amino-terminal domain (NTD), which is conserved among Hsp100 proteins but whose function is unknown, that improve [PSI⁺] propagation. Hsp104147, engineered to lack the NTD, supported [PSI⁺] and functioned normally in thermotolerance and protein disaggregation. Hsp104147 failed to cure [PSI⁺] when overexpressed, however, implying that excess Hsp104 does not eliminate [PSI⁺] by direct dissolution of prion aggregates. Curing of [PSI⁺] by overexpressing catalytically inactive Hsp104 (Hsp104KT), which interferes with endogenous Hsp104, did not require the NTD. We further found that Hsp104 mutants defective in threading peptides through the hexamer pore had reduced ability to support [PSI⁺] in proportion to protein resolubilization defects, suggesting that [PSI⁺] propagation depends on this threading and that Hsp104 "breaks" prion aggregates by extracting protein monomers from the amyloid fibers.

This article has been cited by other articles:

				D. Sharma, R. F. Stanley, and D. C. Masison Curing of Yeast [URE3] Prion by the Hsp40 Cochaperone Ydj1p Is Mediated by Hsp70 Genetics, January 1, 2009; 181(1): 129 - 137. [Abstract] [Full Text] [PDF]

				D. Sharma and D. C. Masison Functionally Redundant Isoforms of a Yeast Hsp70 Chaperone Subfamily Have Different Antiprion Effects Genetics, July 1, 2008; 179(3): 1301 - 1311. [Abstract] [Full Text] [PDF]

				S. N. Bagriantsev, E. O. Gracheva, J. E. Richmond, and S. W. Liebman Variant-specific [PSI+] Infection Is Transmitted by Sup35 Polymers within [PSI+] Aggregates with Heterogeneous Protein Composition Mol. Biol. Cell, June 1, 2008; 19(6): 2433 - 2443. [Abstract] [Full Text] [PDF]

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