Gpd1 Regulates the Activity of Tcp-1 and Heat Shock Response in Yeast Cells: Effect on Aggregation of Mutant Huntingtin

Disruption of the nascent polypeptide-associated complex leads to reduced polyglutamine aggregation and toxicity

The nascent polypeptide-associate complex (NAC) is a heterodimeric chaperone complex that binds near the ribosome exit tunnel and is the first point of chaperone contact for newly synthesized proteins. Deletion of the NAC induces embryonic lethality in many multi-cellular organisms. Previous work has shown that the deletion of the NAC rescues cells from prion-induced cytotoxicity. This counterintuitive result led us to hypothesize that NAC disruption would improve viability in cells expressing human misfolding proteins. Here, we show that NAC disruption improves viability in cells expressing expanded polyglutamine and also leads to delayed and reduced aggregation of expanded polyglutamine and changes in polyglutamine aggregate morphology. Moreover, we show that NAC disruption leads to changes in de novo yeast prion induction. These results indicate that the NAC plays a critical role in aggregate organization as a potential therapeutic target in neurodegenerative disorders.

Identification of potential modulators for human GPD1 by docking-based virtual screening, molecular dynamics simulations, binding free energy calculations, and DeLA-drug analysis

Cytosolic Glycerol-3-phosphate dehydrogenase 1 (GPD1, EC 1.1.1.8) plays a pivotal role in regulating the Embden-Meyerhof glucose glycolysis pathway (E-M pathway), as well as in conditions such as Huntington's disease, cancer, and its potential role as a specific marker for Dormant Glioma Stem Cells. In this study, we conducted virtual screening using the ZINC database ( http://zinc.docking.org/ ) and the GPD1 structure to identify potential GPD1 modulators. The investigation involved screening active candidate ligands using ADMET (Absorption, Distribution, Metabolism, Excretion, Toxicity) parameters, combined with molecular docking, pose analysis, and interaction analysis based on Lipinski and Veber criteria. Subsequently, the top 10 ligands were subjected to 200 ns all-atom molecular dynamics (M.D.) simulations, and binding free energies were calculated. The findings revealed that specific residues, namely TRP14, PRO94, LYS120, ASN151, THR264, ASP260, and GLN298, played a crucial role in ensuring system stability. Furthermore, through a comprehensive analysis involving molecular docking, molecular M.D., and DeLA-Drug, we identified 10 promising small molecules. These molecules represent potential lead compounds for developing effective therapeutics targeting GPD1-associated diseases, thereby contributing to a deeper understanding of GPD1-associated mechanisms. This study's significance lies in identifying key residues associated with GPD1 and discovering valuable small molecules, providing a foundation for further research and development.

Glycerol 3-phosphate dehydrogenase regulates heat shock response in Saccharomyces cerevisiae

The aim of this work was to identify elements of adaptive regulatory mechanism for basal level of yeast histone deacetylase Sir2. Heat shock response (HSR) was altered in the absence of the NAD-dependent glycerol 3-phosphate dehydrogenase (Gpd1). Increase in HSR was lower in ΔGpd1 cells than wild-type cells. An inverse correlation existed between Gpd1 and Sir2; Sir2-deleted cells showed higher expression of Gpd1 while deletion of Gpd1 led to higher expression of Sir2. In the absence of Gpd1, basal activity of Sir2 promoter was higher and was increased further upon heat shock, suggesting higher Sir2 levels. No interaction between Gpd1 and Sir2 was detected without or with heat shock using immunoprecipitation. The results show that Gpd1 regulates HSR in yeast cells and likely blocks its uncontrolled activation. As uncontrolled stress adversely affects the cellular adaptive response, Gpd1 may be a component of the cell's catalogue to ensure a balanced response to unmitigated thermal stress.

Protein aggregation activates erratic stress response in dietary restricted yeast cells

Chronic stress and prolonged activation of defence pathways have deleterious consequences for the cell. Dietary restriction is believed to be beneficial as it induces the cellular stress response machinery. We report here that although the phenomenon is beneficial in a wild-type cell, dietary restriction leads to an inconsistent response in a cell that is already under proteotoxicity-induced stress. Using a yeast model of Huntington's disease, we show that contrary to expectation, aggregation of mutant huntingtin is exacerbated and activation of the unfolded protein response pathway is dampened under dietary restriction. Global proteomic analysis shows that when exposed to a single stress, either protein aggregation or dietary restriction, the expression of foldases like peptidyl-prolyl isomerase, is strongly upregulated. However, under combinatorial stress, this lead is lost, which results in enhanced protein aggregation and reduced cell survival. Successful designing of aggregation-targeted therapeutics will need to take additional stressors into account.