Journal
MOLECULAR MICROBIOLOGY
Volume 115, Issue 6, Pages 1262-1276Publisher
WILEY
DOI: 10.1111/mmi.14671
Keywords
heat shock; Hsp70; Pep4; prion; protein cleavage; protein‐ folding; substrate‐ binding domain
Categories
Funding
- Maynooth University
- Science Foundation Ireland [SFI/13/ISCA2845, RFP/07/BIC493]
- Health Research Board [RP/04/227]
- National Natural Science Foundation of China [31770829, 31920103011]
- Ministry of Science and Technology of China [2017YFA0504000]
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Hsp70 is a conserved chaperone that plays a critical role in maintaining protein homeostasis. Mutations in the SBD disrupt its hydrophobic core, leading to impairment of heat-shock response and prion propagation. The disruption of key residues in the SBD region results in instability and cleavage of Hsp70, impacting its ATPase function and overall stability. This ultimately compromises the stress response and prion propagation abilities of yeast cells.
Hsp70 is an evolutionarily conserved chaperone involved in maintaining protein homeostasis during normal growth and upon exposure to stresses. Mutations in the beta 6/beta 7 region of the substrate-binding domain (SBD) disrupt the SBD hydrophobic core resulting in impairment of the heat-shock response and prion propagation in yeast. To elucidate the mechanisms behind Hsp70 loss of function due to disruption of the SBD, we undertook targeted mutational analysis of key residues in the beta 6/beta 7 region. We demonstrate the critical functional role of the F475 residue across yeast cytosolic Hsp70-Ssa family. We identify the size of the hydrophobic side chain at 475 as the key factor in maintaining SBD stability and functionality. The introduction of amino acid variants to either residue 475, or close neighbor 483, caused instability and cleavage of the Hsp70 SBD and subsequent degradation. Interestingly, we found that Hsp70-Ssa cleavage may occur through a vacuolar carboxypeptidase (Pep4)-dependent mechanism rather than proteasomal. Mutations at 475 and 483 result in compromised ATPase function, which reduces protein re-folding activity and contributes to depletion of cytosolic Hsp70 in vivo. The combination of reduced functionality and stability of Hsp70-Ssa results in yeast cells that are compromised in their stress response and cannot propagate the [PSI+] prion.
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