Hsp31, a member of the DJ-1 superfamily, is a multitasking stress responder with chaperone activity

Abstract

Among different types of protein aggregation, amyloids are a biochemically well characterized state of protein aggregation that are associated with a large number of neurodegenerative diseases including Parkinson's disease, Alzheimer and Creutzfeldt-Jakob disease. Yeast, Saccharomyces cerevisiae is an insightful model to understand the underlying mechanism of protein aggregation. Many yeast molecular chaperones can modulate aggregation and misfolding of proteins including α-Syn and the Sup35 prion. Hsp31 is a homodimeric protein structurally similar to human DJ-1, a Parkinson's disease-linked protein, and both are members of the DJ-1/ThiJ/PfpI superfamily. An emerging view is that Hsp31 and its associated superfamily members each have divergent multitasking functions that have the common theme of responding and managing various types of cellular stress. Hsp31 has several biochemical activities including chaperone and detoxifying enzyme activities that modulate at various points of a stress pathway such as toxicity associated with protein misfolding. However, we have shown the protective role of Hsp31's chaperone activity can operate independent of detoxifying enzyme activities in preventing the early stages of protein aggregate formation and associated cellular toxicities. We provide additional data that collectively supports the multiple functional roles that can be accomplished independent of each other. We present data indicating Hsp31 purified from yeast is more active compared to expression and purification from E. coli suggesting that posttranslational modifications could be important for Hsp31 to be fully active. We also compare the similarities and differences in activities among paralogs of Hsp31 supporting a model in which this protein family has overlapping but diverging roles in responding to various sources of cellular stresses.

Keywords: Hsp31, DJ-1 superfamily; chaperone; degylcase; methylglyoxalase; prion, α-synuclein; stress response.

FIGURE 1.

The hyperbolic plot of substrate concentration versus rate of D-lactate production by Hsp31 (circles), MORF Hsp31 (squares) and DJ-1 (triangles) are shown and the solid line represents the Michaelis-Menten best-fit model. The Vmax parameters were determined based on this model.

FIGURE 2.

Hsp31 cannot resolve the Sup35 amyloids. [PSI+] cells were transferred with pAG415-GPD-Hsp31-DsRed, p2HG Hsp104 and their corresponding empty vectors. Cultures were incubated at 30°C for 16 hrs before plating on ¼ YPD medium to develop colony color. Change from white to red color phenotype demonstrated curing. Hsp104 is able to cure the [PSI+] phenotype as seen by the red colonies. Hsp31 expression under these conditions can transiently reduce prion aggregation as shown by semi-denaturing gels and microscopy but is not able to cure prions.

FIGURE 3.

The homeostatic functions of Hsp31 associated with protecting cells from stress. Hsp31 is a methylglyoxalase that converts MGO into D-lactate independent of glutathione. Proteotoxic stress induced the expression of Hsp31, which exerts a protective function against toxic effect of oligomers in yeast cells. Oxidative stress induces the expression of Hsp31, re-localizes it to mitochondria resulting in reduced levels of ROS. Response to other stresses leads to Hsp31 localization to P bodies and stress granules. HSP31 deletion under carbon starvation compromises the autophagy pathway, which is a pathway used to clear oligomerized or aggregated proteins. Despite the role of Hsp31 in autophagy, it has a protective effect against α-Syn oligomerization independent of its role in autophagy because of its inhibitory effect early in the oligomerization process.