Project description:The hop plant, Humulus lupulus L., contains an exceptionally high content of secondary metabolites, the hop iso-α-acids, which possess a range of beneficial properties including antiseptic action. Studies performed on the mode of action of hop iso-α-acids have hitherto been restricted to lactic acid bacteria. The present study investigates molecular mechanisms of hop iso-α-acid resistance in the model eukaryote Saccharomyces cerevisiae. Growth inhibition occurred at concentrations of hop iso-α-acids that were an order of magnitude higher than those found with hop-tolerant prokaryotes. Chemostat-based transcriptome analysis and phenotype screening of the S. cerevisiae haploid gene deletion collection were used as complementary methods to screen for genes involved in hop iso-α-acids detoxification and tolerance. Further analysis of deletion mutants confirmed that yeast tolerance to hop iso-α-acids involves two major processes: active export of iso-α-acids across the plasma membrane and active proton pumping into the vacuole by the V-ATPase to enable vacuolar sequestration of iso-α-acids. Furthermore, iso-α-acids were shown to affect cellular metal homeostasis by acting as strong zinc and iron chelator.
Project description:The hop plant, Humulus lupulus L., contains an exceptionally high content of secondary metabolites, the hop iso-α-acids, which possess a range of beneficial properties including antiseptic action. Studies performed on the mode of action of hop iso-α-acids have hitherto been restricted to lactic acid bacteria. The present study investigates molecular mechanisms of hop iso-α-acid resistance in the model eukaryote Saccharomyces cerevisiae. Growth inhibition occurred at concentrations of hop iso-α-acids that were an order of magnitude higher than those found with hop-tolerant prokaryotes. Chemostat-based transcriptome analysis and phenotype screening of the S. cerevisiae haploid gene deletion collection were used as complementary methods to screen for genes involved in hop iso-α-acids detoxification and tolerance. Further analysis of deletion mutants confirmed that yeast tolerance to hop iso-α-acids involves two major processes: active export of iso-α-acids across the plasma membrane and active proton pumping into the vacuole by the V-ATPase to enable vacuolar sequestration of iso-α-acids. Furthermore, iso-α-acids were shown to affect cellular metal homeostasis by acting as strong zinc and iron chelator. Experiment Overall Design: Two complementary genome-wide approaches were employed to investigate cellular responses of S. cerevisiae to hop extracts enriched in iso-α-acids. Microarray transcriptome analysis was performed on chemostat cultures of an S. cerevisiae reference strain grown in the presence and absence of iso-α-acids. In addition, screening of the nearly complete set of yeast open reading frame (ORF) haploid knock-outs generated by the Saccharomyces Genome Deletion Project (SGDP) (Open Biosystems) identified the mutants with increased hop sensitivity. Subsequently, involvement of selected genes and cellular processes in hop acid sensitivity and tolerance was analyzed by construction and detailed analysis of selected mutant strains.
Project description:Scope: Alcoholic liver disease (ALD) is a major cause of chronic liver disease and is induced by alcohol consumption. Acetaldehyde produced by alcohol metabolism enhances the fibrosis of the liver through hepatic stellate cells. Additionally, alcohol administration causes the accumulation of reactive oxygen species (ROS), which induce hepatocyte-injury-mediated lipid peroxidation. The purpose of this study was to investigate the protective effects of iso-α-acids against alcoholic liver injury in hepatocytes in mice. Methods and results: C57BL/6N mice were fed diets containing isomerized hop extract, which mainly consists of iso-α-acids. After 7 days of feeding, acetaldehyde was administered by a single intraperitoneal injection. The acetaldehyde-induced increases in serum AST and ALT levels were suppressed by iso-α-acids intake. Hepatic gene expression analyses showed the upregulation of the glutathione-S-transferase, alcohol dehydrogenase and aldehyde dehydrogenase genes. In vitro, iso-α-acids induced the nuclear translocation of nuclear factor erythroid 2-like 2 (Nfe2l2; Nrf2), a master regulator of antioxidant and detoxifying systems, and upregulated the enzymatic activities of glutathione-S-transferase and aldehyde dehydrogenase. Conclusions: These results suggest that iso-α-acids intake prevents alcoholic liver disease injury by reducing oxidative stress via the Nrf2-mediated pathway.
Project description:Plant vacuoles serve as the primary intracellular compartments for inorganic phosphate (Pi) storage. Passage of Pi across vacuolar membranes plays a critical role in buffering the cytoplasmic Pi level against fluctuations of external Pi and metabolic activities. Here we demonstrate that the SPX-MFS proteins, designated as Phosphate Transporter 5 family (PHT5), also named Vacuolar Phosphate Transporter (VPT), function as vacuolar Pi transporters. Based on 31P-magnetic resonance spectroscopy analysis, Arabidopsis pht5;1 loss-of-function mutants accumulate less Pi and exhibit a lower vacuolar-to-cytoplasmic Pi ratio than controls. Conversely, overexpression of PHT5 leads to massive Pi sequestration into vacuoles and altered regulation of Pi starvation-responsive genes. Furthermore, we show that heterologous expression of OsSPX-MFS1, the rice PHT5 homolog, mediates Pi influx to yeast vacuoles. Our findings uncover a group of Pi transporters in vacuolar membranes that regulate the cytoplasmic Pi homeostasis required for the fitness of plant growth. 10-day seedlings grown on Pi-sufficient medium or followed by 1-day or 3-day Pi starvation, shoot RNA and root RNA were extracted separately
Project description:Amino acid homeostasis is critical for many cellular processes. It is well established that amino acids are compartmentalized using pH gradients generated between organelles and the cytoplasm; however, the dynamics of this partitioning has not been explored. We have developed a highly sensitive pH reporter, and we find that the major amino acid storage compartment in Saccharomyces cerevisiae, the lysosome-like vacuole, alkalinizes prior to cell division and re-acidifies as cells divide. The vacuolar pH dynamics require the uptake of extracellular amino acids and activity of TORC1, the v-ATPase and the cycling of the vacuolar specific lipid, PI3,5P2 which is regulated by the cyclin-dependent kinase, CDK5/Pho85. Vacuolar pH regulation enables amino acid sequestration and mobilization from the organelle, which is important for mitochondrial function, ribosome homeostasis and cell size control. Collectively, our data provide a new paradigm for the use of dynamic pH-dependent amino acid compartmentalization during cell growth/division.
Project description:Plant vacuoles serve as the primary intracellular compartments for inorganic phosphate (Pi) storage. Passage of Pi across vacuolar membranes plays a critical role in buffering the cytoplasmic Pi level against fluctuations of external Pi and metabolic activities. Here we demonstrate that the SPX-MFS proteins, designated as Phosphate Transporter 5 family (PHT5), also named Vacuolar Phosphate Transporter (VPT), function as vacuolar Pi transporters. Based on 31P-magnetic resonance spectroscopy analysis, Arabidopsis pht5;1 loss-of-function mutants accumulate less Pi and exhibit a lower vacuolar-to-cytoplasmic Pi ratio than controls. Conversely, overexpression of PHT5 leads to massive Pi sequestration into vacuoles and altered regulation of Pi starvation-responsive genes. Furthermore, we show that heterologous expression of OsSPX-MFS1, the rice PHT5 homolog, mediates Pi influx to yeast vacuoles. Our findings uncover a group of Pi transporters in vacuolar membranes that regulate the cytoplasmic Pi homeostasis required for the fitness of plant growth.
Project description:Biogenesis of eukaryotic messenger ribonucleoprotein complexes (mRNPs) involves the synthesis, splicing, and 3’-processing of pre-mRNA, and the assembly of mature mRNPs for nuclear export. We mapped 23 mRNP biogenesis factors onto the newly synthesized yeast transcriptome, providing ~10^5-10^6 high-confidence RNA interaction sites per factor.
Project description:Folding of stringent clients requires transfer from Hsp70 to Hsp90. The co-chaperone Hop physically connects the chaperone machineries. Here we define its role from the remodeling of Hsp70/40-client complexes to the mechanism of client transfer and the conformational switching from stalled to active client-processing states of Hsp90. We show that Hsp70 together with Hsp40 completely unfolds a stringent client, the glucocorticoid receptor ligand binding domain (GR-LBD) in large assemblies. Hop remodels these for efficient transfer onto Hsp90. As p23 enters, Hsp70 leaves the complex via switching between binding sites in Hop. To proceed to client folding, current concepts assume that Hop dissociates and the co-chaperone p23 stabilizes the Hsp90 closed state. In contrast, we show that p23 directly interacts with Hop, relieves the stalling Hsp90-Hop interaction and closes Hsp90. This reaction allows folding of the client and is thus the key regulatory step for the progression of the chaperone cycle. To study the interaction between the different proteins, especially p23 and the DP2 domain of Hop, we performed crosslinking-MS.
Project description:Biogenesis of eukaryotic messenger ribonucleoprotein complexes (mRNPs) involves the synthesis, splicing, and 3M-bM-^@M-^Y-processing of pre-mRNA, and the assembly of mature mRNPs for nuclear export. We mapped 23 mRNP biogenesis factors onto the newly synthesized yeast transcriptome, providing ~10^5-10^6 high-confidence RNA interaction sites per factor. PAR-CLIP data of 23 mRNP biogenesis factors in Saccharomyces cerevisiae