The small heat shock protein Hsp31 cooperates with Hsp104 to modulate Sup35 prion aggregation

Saccharomyces cerevisiae DJ-1 paralogs maintain genome integrity through glycation repair of nucleic acids and proteins

Reactive carbonyl species (RCS) such as methylglyoxal and glyoxal are potent glycolytic intermediates that extensively damage cellular biomolecules leading to genetic aberration and protein misfolding. Hence, RCS levels are crucial indicators in the progression of various pathological diseases. Besides the glyoxalase system, emerging studies report highly conserved DJ-1 superfamily proteins as critical regulators of RCS. DJ-1 superfamily proteins, including the human DJ-1, a genetic determinant of Parkinson's disease, possess diverse physiological functions paramount for combating multiple stressors. Although S. cerevisiae retains four DJ-1 orthologs (Hsp31, Hsp32, Hsp33, and Hsp34), their physiological relevance and collective requirement remain obscure. Here, we report for the first time that the yeast DJ-1 orthologs function as novel enzymes involved in the preferential scavenge of glyoxal and methylglyoxal, toxic metabolites, and genotoxic agents. Their collective loss stimulates chronic glycation of the proteome, and nucleic acids, inducing spectrum of genetic mutations and reduced mRNA translational efficiency. Furthermore, the Hsp31 paralogs efficiently repair severely glycated macromolecules derived from carbonyl modifications. Also, their absence elevates DNA damage response, making cells vulnerable to various genotoxins. Interestingly, yeast DJ-1 orthologs preserve functional mitochondrial content, maintain ATP levels, and redistribute into mitochondria to alleviate the glycation damage of macromolecules. Together, our study uncovers a novel glycation repair pathway in S. cerevisiae and a possible neuroprotective mechanism of how hDJ-1 confers mitochondrial health during glycation toxicity.

Redox-dependent regulation of mitochondrial dynamics by DJ-1 paralogs in Saccharomyces cerevisiae

Mitochondria are indispensable organelles that perform critical cellular functions, including energy metabolism, neurotransmission, and synaptic maintenance. Mitochondrial dysfunction and impairment in the organellar homeostasis are key hallmarks implicated in the progression of neurodegenerative disorders. The members of DJ-1/ThiJ/PfpI family are highly conserved, and loss of DJ-1 (PARK7) function in humans results in the impairment of mitochondrial homeostasis, which is one of the key cellular etiology implicated in the progression of Parkinson's Disease. However, the underlying molecular mechanism involved in mitochondrial maintenance and other cellular processes by DJ-1 paralogs is poorly understood. By utilizing genetic approaches from S. cerevisiae, we uncovered intricate mechanisms associated with the mitochondrial phenotypic variations regulated by DJ-1 paralogs. The deletion of DJ-1 paralogs led to respiratory incompetence and the accumulation of enhanced functional mitochondrial mass. The lack of DJ-1 paralogs also displayed enriched mitochondrial interconnectivity due to upregulation in the fusion-mediating proteins, facilitated by the elevation in the basal cellular ROS and oxidized glutathione levels. Intriguingly, these mitochondrial phenotypes variations cause cell size abnormalities, partially suppressed by reestablishing redox balance and upregulation of fission protein levels. Besides, in the absence of DJ-1 paralogs, cells exhibited a significant delay in the cell-cycle progression in the G2/M phase, attributed to mitochondrial hyperfusion and partial DNA damage. Additionally, the aberrations in mitochondrial dynamics and cell-cycle induce cell death mediated by apoptosis. Taken together, our findings first-time provide evidence to show how DJ-1 family members regulate mitochondrial homeostasis and other intricate cellular processes, including cell cycle and apoptosis.

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Lack of DJ-1 members causes respiratory incompetence and elevated basal ROS levels.

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Enhanced ROS and GSSG levels promote increased mitochondrial mass and hyperfusion.

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Mitochondrial hyperfusion together with ROS-induced DNA damage cause G2/M arrest.

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Impairment in cell cycle progression triggers apoptotic cell death in yeast.

Oxidative stress triggers aggregation of GFP-tagged Hsp31p, the budding yeast environmental stress response chaperone, and glyoxalase III

The Saccharomyces cerevisiae Hsp31p protein belongs to the ubiquitous DJ-1/ThiJ/PfpI family. The most prominent member of this family is human DJ-1; defects of this protein are associated with Parkinson's disease pathogenesis. Numerous recent findings reported by our group and others have revealed the importance of Hsp31p for survival in the post-diauxic phase of cell growth and under diverse environmental stresses. Hsp31p was shown to possess glutathione-independent glyoxalase III activity and to function as a protein chaperone, suggesting that it has multiple cellular roles. Our previous work also revealed that HSP31 gene expression was controlled by multiple stress-related transcription factors, which mediated HSP31 promoter responses to oxidative, osmotic, and thermal stresses, toxic products of glycolysis, and the diauxic shift. Nevertheless, the exact role of Hsp31p within budding yeast cells remains elusive. Here, we aimed to obtain insights into the function of Hsp31p based on its intracellular localization. We have demonstrated that the Hsp31p-GFP fusion protein is localized to the cytosol under most environmental conditions and that it becomes particulate in response to oxidative stress. However, the particles do not colocalize with other granular subcellular structures present in budding yeast cells. The observed particulate localization does not seem to be important for Hsp31p functionality. Instead, it is likely the result of oxidative damage, as the particle abundance increases when Hsp31p is nonfunctional, when the cellular oxidative stress response is affected, or when cellular maintenance systems that optimize the state of the proteome are compromised.

Protein aggregation in cell biology: An aggregomics perspective of health and disease

Maintaining protein homeostasis (proteostasis) is essential for cellular health and is governed by a network of quality control machinery comprising over 800 genes. When proteostasis becomes imbalanced, proteins can abnormally aggregate or become mislocalized. Inappropriate protein aggregation and proteostasis imbalance are two of the central pathological features of common neurodegenerative diseases including Alzheimer, Parkinson, Huntington, and motor neuron diseases. How aggregation contributes to the pathogenic mechanisms of disease remains incompletely understood. Here, we integrate some of the key and emerging ideas as to how protein aggregation relates to imbalanced proteostasis with an emphasis on Huntington disease as our area of main expertise. We propose the term "aggregomics" be coined in reference to how aggregation of particular proteins concomitantly influences the spatial organization and protein-protein interactions of the surrounding proteome. Meta-analysis of aggregated interactomes from various published datasets reveals chaperones and RNA-binding proteins are common components across various disease contexts. We conclude with an examination of therapeutic avenues targeting proteostasis mechanisms.