The noncanonical small heat shock protein HSP-17 from Caenorhabditis elegans is a selective protein aggregase

Abstract

Small heat shock proteins (sHsps) are conserved, ubiquitous members of the proteostasis network. Canonically, they act as “holdases” and buffer unfolded or misfolded proteins against aggregation in an ATP-independent manner. Whereas bacteria and yeast each have only two sHsps in their genomes, this number is higher in metazoan genomes, suggesting a spatiotemporal and functional specialization in higher eukaryotes. Here, using recombinantly expressed and purified proteins, static light-scattering analysis, and disaggregation assays, we report that the noncanonical sHsp HSP-17 of Caenorhabditis elegans facilitates aggregation of model substrates, such as malate dehydrogenase (MDH), and inhibits disaggregation of luciferase in vitro. Experiments with fluorescently tagged HSP-17 under the control of its endogenous promoter revealed that HSP-17 is expressed in the digestive and excretory organs, where its overexpression promotes the aggregation of polyQ proteins and of the endogenous kinase KIN-19. Systemic depletion of hsp-17 shortens C. elegans lifespan and severely reduces fecundity and survival upon prolonged heat stress. HSP-17 is an abundant protein exhibiting opposing chaperone activities on different substrates, indicating that it is a selective protein aggregase with physiological roles in development, digestion, and osmoregulation.

Come Together: Protein Assemblies, Aggregates and the Sarcostat at the Heart of Cardiac Myocyte Homeostasis

“…The most impressive demonstration of the significance of sHsp homologs appears to be in C. elegans where the lifespan prolongation in the ultra-long-lived insulin resistant daf-2 mutant was dependent on protein aggregates containing the CryAB homolog Hsp16.1 (Walther et al, 2015). Furthermore, recent work indicates that a non-canonical sHsp (Hsp-17) functions as an "aggregase" and loss of function mutants have shorter lifespan (Iburg et al, 2020). Similarly, the yeast analog Hsp42, harboring a prion-like domain in the N-terminus, is endowed with both chaperone and aggregase functions (Grousl et al, 2018).…”

Identification of a HTT-specific binding motif in DNAJB1 essential for suppression and disaggregation of HTT

“…Luciferase assay was performed according to previously published protocols 47 , 50 . Briefly, a 15 nM luciferase solution in 1× dilution buffer (50 mM HEPES pH 7.4, 100 mM KCl, 5 mM MgCl 2 , 1 mM DTT, 10 µM BSA, 3.5 µM Pyruvate Kinase (Sigma-Aldrich, #P7768), 3 mM Phosphoenol Pyruvate) was denatured at 45 °C for 15 min.…”

Hyperactivation of the proteasome core particle in Caenorhabditis elegans protects against proteotoxic stress and extends lifespan

“…More specifically, proteins in the HSP-16 family act as passive ligands to prevent aggregation and are known to be upregulated under conditions of oxidative stress 78 as well as during treatment with protein damaging compounds 79 . HSP-17 has been shown to prevent aggregation of specific proteins, although its mechanism of action remains unclear 80 . Previous studies have shown that sHSPs are upregulated in many long-lived mutants including daf-2 81,82 , which is consistent with the observation that increased proteostasis protects from aging.…”