TORC1 Regulates Pah1 Phosphatidate Phosphatase Activity via the Nem1/Spo7 Protein Phosphatase Complex

The evolutionarily conserved target of rapamycin complex 1 (TORC1) controls growth-related processes such as protein, nucleotide, and lipid metabolism in response to growth hormones, energy/ATP levels, and amino acids. Its deregulation is associated with cancer, type 2 diabetes, and obesity. Among other substrates, mammalian TORC1 directly phosphorylates and inhibits the phosphatidate phosphatase lipin-1, a central enzyme in lipid metabolism that provides diacylglycerol for the synthesis of membrane phospholipids and/or triacylglycerol as neutral lipid reserve. Here, we show that yeast TORC1 inhibits the function of the respective lipin, Pah1, to prevent the accumulation of triacylglycerol. Surprisingly, TORC1 regulates Pah1 in part indirectly by controlling the phosphorylation status of Nem1 within the Pah1-activating, heterodimeric Nem1-Spo7 protein phosphatase module. Our results delineate a hitherto unknown TORC1 effector branch that controls lipin function in yeast, which, given the recent discovery of Nem1-Spo7 orthologous proteins in humans, may be conserved.     

In vivo biosensors

Detailed understanding of the dynamics of living systems requires a means to monitor, in real time, changes in the levels of key components in response to specific stimuli. Applications involving cultured cells, tissue slices and implantation in living systems are discussed.     

Staphylococcal enterotoxin A: Partial unfolding caused by high pressure or denaturing agents enhances superantigenicity

The effect of transient exposure of Staphylococcus aureus enterotoxin A (SEA) to high pressure and/or denaturing agents was examined by assessing the toxin superantigenicity and immunoreactivity, and by monitoring pressure-induced changes in fluorescence emission spectra. Pressurization of SEA at 600 MPa and 45 °C in Tris–HCl buffer (20 mM, pH 7.4) resulted in a marked increase in both T-cell proliferation (superantigenicity) and immunoreactivity. In opposite, pressurization at 20 °C did not change significantly SEA superantigenicity and immunoreactivity, indicating some toxin baro-resistance. Exposure of SEA to 8 M urea at atmospheric pressure or at 600 MPa and 20 °C, also led to a marked increase of superantigenicity (but not of immunoreactivity). In contrast, exposure of SEA to sodium-dodecylsulfate (30 mM) led to an increase of immunoreactivity with some effect on superantigenicity after pressurization at 45 °C only. High pressure up to 600 MPa induced spectral changes which at 20 °C were fully reversible upon decompression. At 45 °C, however, a sharp break of the centre of spectral mass mainly due to tryptophan residues was observed at 300 MPa, and irreversible spectral changes mainly related to tyrosine residues subsisted after pressure release, indicating a marked protein conformational transition. Urea 8 M further increased SEA structural changes at 600 MPa and 20 °C. These results indicate that SEA, under a combination of high pressure and mild temperature, as well as in the presence of urea, partly unfolds to a structure of strongly increased T-cell proliferative ability.     

GUP1 of Saccharomyces cerevisiae encodes an O-acyltransferase involved in remodeling of the GPI anchor

The anchors of mature glycosylphosphatidylinositol (GPI)-anchored proteins of Saccharomyces cerevisiae contain either ceramide or diacylglycerol with a C26:0 fatty acid in the sn2 position. The primary GPI lipid added to newly synthesized proteins in the ER consists of diacylglycerol with conventional C16 and C18 fatty acids. Here we show that GUP1 is essential for the synthesis of the C26:0-containing diacylglycerol anchors. Gup1p is an ER membrane protein with multiple membrane-spanning domains harboring a motif that is characteristic of membrane-bound O-acyl-transferases (MBOAT). Gup1Delta cells make normal amounts of GPI proteins but most mature GPI anchors contain lyso-phosphatidylinositol, and others possess phosphatidylinositol with conventional C16 and C18 fatty acids. The incorporation of the normal ceramides into the anchors is also disturbed. As a consequence, the ER-to-Golgi transport of the GPI protein Gas1p is slow, and mature Gas1p is lost from the plasma membrane into the medium. Gup1Delta cells have fragile cell walls and a defect in bipolar bud site selection. GUP1 function depends on the active site histidine of the MBOAT motif. GUP1 is highly conserved among fungi and protozoa and the gup1Delta phenotype is partially corrected by GUP1 homologues of Aspergillus fumigatus and Trypanosoma cruzi.     

Assessment of acrosomal status in rat spermatozoa: studies on carbohydrate and non-carbohydrate agonists

In the mouse and several other species, including man, capacitated acrosome-intact spermatozoa interact with natural [soluble zona pellucida (ZP) and progesterone (P4)] and synthetic [neoglycoproteins (ngps) and calcium (Ca(2+)) ionophore] agonists, prior to the initiation of a Ca(2+)-dependent signal transduction cascade. The net result is the fusion of the sperm plasma membrane overlying the outer acrosomal membrane at multiple sites and exocytosis of acrosomal contents [i.e., induction of the acrosome reaction (AR)]. This step is believed to be a prerequisite that enables the acrosome-reacted spermatozoon to penetrate the ZP and fertilize the egg. Although the rat is one of the most commonly used laboratory animals, very little is known about the chemical nature of agonists that induce the AR in this species. The lack of this information is primarily due to the fact that the rat sperm acrosome is a relatively thin structure. Thus, it is difficult to assess the status of the sperm acrosome in this species. In this report, we describe the use of a Coomassie brilliant blue dye staining procedure to assess the status of the rat sperm acrosome by light microscopy. The procedure is highly reproducible and has allowed us to determine the effects of carbohydrate (ngps and mouse ZP) and noncarbohydrate (P4 and Ca(2+) ionophore) agonists on capacitated spermatozoa. In addition, we have used a pharmacological approach to examine the functional significance of calmodulin (CaM), a Ca(2+)-binding protein, in induction of the AR in spermatozoa. Data presented in this report demonstrate that several ngps, solubilized mZP, P4, and Ca(2+) ionophores induce the AR in rat spermatozoa. Furthermore, we demonstrate that, whereas CaM antagonists blocked P4-induced AR, most of the inhibitors used had no significant effect on the Ca(2+) ionophore-induced (nonphysiological) AR.     

Characterization of Leishmania donovani aquaporins shows presence of subcellular aquaporins similar to tonoplast intrinsic proteins of plants

Leishmania donovani, a protozoan parasite, resides in the macrophages of the mammalian host. The aquaporin family of proteins form important components of the parasite-host interface. The parasite-host interface could be a potential target for chemotherapy. Analysis of L. major and L. infantum genomes showed the presence of five aquaporins (AQPs) annotated as AQP9 (230aa), AQP putative (294aa), AQP-like protein (279aa), AQP1 (314aa) and AQP-like protein (596aa). We report here the structural modeling, localization and functional characterization of the AQPs from L. donovani. LdAQP1, LdAQP9, LdAQP2860 and LdAQP2870 have the canonical NPA-NPA motifs, whereas LdAQP putative has a non-canonical NPM-NPA motif. In the carboxyl terminal to the second NPA box of all AQPs except AQP1, a valine/alanine residue was found instead of the arginine. In that respect these four AQPs are similar to tonoplast intrinsic proteins in plants, which are localized to intracellular organelles. Confocal microscopy of L. donovani expressing GFP-tagged AQPs showed an intracellular localization of LdAQP9 and LdAQP2870. Real-time PCR assays showed expression of all aquaporins except LdAQP2860, whose level was undetectable. Three-dimensional homology modeling of the AQPs showed that LdAQP1 structure bears greater topological similarity to the aquaglyceroporin than to aquaporin of E. coli. The pore of LdAQP1 was very different from the rest in shape and size. The cavity of LdAQP2860 was highly irregular and undefined in geometry. For functional characterization, four AQP proteins were heterologously expressed in yeast. In the fps1Δ yeast cells, which lacked the key aquaglyceroporin, LdAQP1 alone displayed an osmosensitive phenotype indicating glycerol transport activity. However, expression of LdAQP1 and LdAQP putative in a yeast gpd1Δ strain, deleted for glycerol production, conferred osmosensitive phenotype indicating water transport activity or aquaporin function. Our analysis for the first time shows the presence of subcellular aquaporins and provides structural and functional characterization of aquaporins in Leishmania donovani.     

Functional SARS-CoV-2-Specific Immune Memory Persists after Mild COVID-19

1. Download : Download high-res image (133KB)
2. Download : Download full-size image

     

Multiple-step virtual screening using VSM-G: overview and validation of fast geometrical matching enrichment

Numerous methods are available for use as part of a virtual screening strategy but, as yet, no single method is able to guarantee both a level of confidence comparable to experimental screening and a level of computing efficiency that could drastically cut the costs of early phase drug discovery campaigns. Here, we present VSM-G (virtual screening manager for computational grids), a virtual screening platform that combines several structure-based drug design tools. VSM-G aims to be as user-friendly as possible while retaining enough flexibility to accommodate other in silico techniques as they are developed. In order to illustrate VSM-G concepts, we present a proof-of-concept study of a fast geometrical matching method based on spherical harmonics expansions surfaces. This technique is implemented in VSM-G as the first module of a multiple-step sequence tailored for high-throughput experiments. We show that, using this protocol, notable enrichment of the input molecular database can be achieved against a specific target, here the liver-X nuclear receptor. The benefits, limitations and applicability of the VSM-G approach are discussed. Possible improvements of both the geometrical matching technique and its implementation within VSM-G are suggested. Figure Basic principle of the virtual screening funnel process.