The Saccharomyces cerevisiae Spo7 basic tail is required for Nem1-Spo7/Pah1 phosphatase cascade function in lipid synthesis

The Saccharomyces cerevisiae Nem1-Spo7 protein phosphatase complex dephosphorylates and thereby activates Pah1 at the nuclear/endoplasmic reticulum membrane. Pah1, a phosphatidate phosphatase catalyzing the dephosphorylation of phosphatidate to produce diacylglycerol, is one of the most highly regulated enzymes in lipid metabolism. The diacylglycerol produced in the lipid phosphatase reaction is utilized for the synthesis of triacylglycerol that is stored in lipid droplets. Disruptions of the Nem1-Spo7/Pah1 phosphatase cascade cause a plethora of physiological defects. Spo7, the regulatory subunit of the Nem1-Spo7 complex, is required for the Nem1 catalytic function and interacts with the acidic tail of Pah1. Spo7 contains three conserved homology regions (CR1-3) that are important for the interaction with Nem1, but its region for the interaction with Pah1 is unknown. Here, by deletion and site-specific mutational analyses of Spo7, we revealed that the C-terminal basic tail (residues 240-259) containing five arginine and two lysine residues is important for the Nem1-Spo7 complex-mediated dephosphorylation of Pah1 and its cellular function (triacylglycerol synthesis, lipid droplet formation, maintenance of nuclear/endoplasmic reticulum membrane morphology, and cell growth at elevated temperatures). The glutaraldehyde cross-linking analysis of synthetic peptides indicated that the Spo7 basic tail interacts with the Pah1 acidic tail. This work advances our understanding of the Spo7 function and the Nem1-Spo7/Pah1 phosphatase cascade in yeast lipid synthesis.

Conserved regions of the regulatory subunit Spo7 are required for Nem1-Spo7/Pah1 phosphatase cascade function in yeast lipid synthesis

In the yeast Saccharomyces cerevisiae, the Nem1-Spo7 complex is a protein phosphatase that activates Pah1 phosphatidate (PA) phosphatase at the nuclear/endoplasmic reticulum membrane for the synthesis of triacylglycerol. The Nem1-Spo7/Pah1 phosphatase cascade largely controls whether PA is partitioned into the storage lipid triacylglycerol or into membrane phospholipids. The regulated synthesis of the lipids is crucial for diverse physiological processes during cell growth. Spo7 in the protein phosphatase complex is required as a regulatory subunit for the Nem1 catalytic subunit to dephosphorylate Pah1. The regulatory subunit contains three conserved homology regions (CR1, CR2, and CR3). Previous work showed that the hydrophobicity of LLI (residues 54-56) within CR1 is important for Spo7 function in the Nem1-Spo7/Pah1 phosphatase cascade. In this work, by deletion and site-specific mutational analyses, we revealed that CR2 and CR3 are also required for Spo7 function. Mutations in any one of the conserved regions were sufficient to disrupt the function of the Nem1-Spo7 complex. We determined that the uncharged hydrophilicity of STN (residues 141-143) within CR2 was required for Nem1-Spo7 complex formation. Additionally, the hydrophobicity of LL (residues 217 and 219) within CR3 was important for Spo7 stability, which indirectly affected complex formation. Finally, we showed the loss of Spo7 CR2 or CR3 function by the phenotypes (e.g., reduced amounts of triacylglycerol and lipid droplets, temperature sensitivity) that are attributed to defects in membrane translocation and dephosphorylation of Pah1 by the Nem1-Spo7 complex. These findings advance knowledge of the Nem1-Spo7 complex and its role in lipid synthesis regulation.

Mutant phosphatidate phosphatase Pah1-W637A exhibits altered phosphorylation, membrane association, and enzyme function in yeast

The Saccharomyces cerevisiae PAH1-encoded phosphatidate (PA) phosphatase, which catalyzes the dephosphorylation of PA to produce diacylglycerol, controls the bifurcation of PA into triacylglycerol synthesis and phospholipid synthesis. Pah1 is inactive in the cytosol as a phosphorylated form and becomes active on the membrane as a dephosphorylated form by the Nem1–Spo7 protein phosphatase. We show that the conserved Trp-637 residue of Pah1, located in the intrinsically disordered region, is required for normal synthesis of membrane phospholipids, sterols, triacylglycerol, and the formation of lipid droplets. Analysis of mutant Pah1-W637A showed that the tryptophan residue is involved in the phosphorylation-mediated/dephosphorylation-mediated membrane association of the enzyme and its catalytic activity. The endogenous phosphorylation of Pah1-W637A was increased at the sites of the N-terminal region but was decreased at the sites of the C-terminal region. The altered phosphorylation correlated with an increase in its membrane association. In addition, membrane-associated PA phosphatase activity in vitro was elevated in cells expressing Pah1-W637A as a result of the increased membrane association of the mutant enzyme. However, the inherent catalytic function of Pah1 was not affected by the W637A mutation. Prediction of Pah1 structure by AlphaFold shows that Trp-637 and the catalytic residues Asp-398 and Asp-400 in the haloacid dehalogenase-like domain almost lie in the same plane, suggesting that these residues are important to properly position the enzyme for substrate recognition at the membrane surface. These findings underscore the importance of Trp-637 in Pah1 regulation by phosphorylation, membrane association of the enzyme, and its function in lipid synthesis.

Hormonal regulation of glycine decarboxylase and its relationship to oxidative stress

In both humans and rodent models, circulating glycine levels are significantly reduced in obesity, glucose intolerance, type II diabetes, and non-alcoholic fatty liver disease. The glycine cleavage system and its rate-limiting enzyme, glycine decarboxylase (GLDC), is a major determinant of plasma glycine levels. The goals of this study were to determine if the increased expression of GLDC contributes to the reduced plasma glycine levels seen in disease states, to characterize the hormonal regulation of GLDC gene expression, and to determine if altered GLDC expression has physiological effects that might affect the development of diabetes. The findings presented here show that hepatic GLDC gene expression is elevated in mouse models of obesity and diabetes, as well as by fasting. We demonstrated that GLDC gene expression is strongly regulated by the metabolic hormones glucagon and insulin, and we identified the signaling pathways involved in this regulation. Finally, we found that GLDC expression is linked to glutathione levels, with increased expression associated with elevated levels of glutathione and reduced expression associated with a suppression of glutathione and increased cellular ROS levels. These findings suggest that the hormonal regulation of GLDC contributes not only to the changes in circulating glycine levels seen in metabolic disease, but also affects glutathione production, possibly as a defense against metabolic disease-associated oxidative stress.

Plant growth promoting potential and soil enzyme production of the most abundant Streptomyces spp. from wheat rhizosphere

AIM

To evaluate the plant growth promotion (PGP) potential and soil enzyme production under solid state fermentation (SSF) by most abundant Streptomyces spp. isolated from the wheat rhizosphere and to evaluate their effect on plant growth parameters.

METHODS AND RESULTS

Actinomycetes were isolated from wheat rhizosphere and screened for PGP activities. Three actinomycete isolates having significantly higher PGP activities (Streptomyces rochei IDWR19, Streptomyces carpinensis IDWR53, Streptomyces thermolilacinus IDWR81) were selected. The soil enzymes production potential of these isolates using soil extract and wheat straw under ssf was assessed. Utilization of soil extract as a fermentation medium for soil enzyme production by Actinomycetes has been reported first time in this study. Maximum chitinase (S. rochei IDWR19 12·2 U mg(-1) protein) and phytase activity (S. carpinensis IDWR53 5·2 U mg(-1) protein) was produced on 7th day of incubation, whereas maximum alkaline protease (S. rochei IDWR19 3·2 U mg(-1) protein) was produced on 6th day of incubation. For cellulase (S. rochei IDWR19 7·4 U mg(-1) protein) and invertase (S. carpinensis IDWR53 451 U mg(-1) protein) maximum activity was observed on 4th as well as 5th day of incubation. On the basis of PGP activity and enzyme production, two actinomycete isolates (S. rochei IDWR19 and S. thermolilacinus IDRWR81) were selected for plant growth experiment. An increase of 12·2 and 24·5% in shoot length of plants inoculated with S. rochei IDWR19 and S. thermolilacinus IDWR81 was observed, respectively. A similar increase in biomass of 1·8- and 2·3-fold was also recorded for the two isolates, respectively.

CONCLUSIONS

It could be concluded that Streptomyces sp. with high PGP activities and soil enzyme production capability significantly improved growth and development of wheat cv.

SIGNIFICANCE AND IMPACT OF THE STUDY

The abundant Actinomycetes obtained in this study (S. rochei IDWR19 and S. thermolilacinus IDWR81) are rhizosphere competent and effective strains.