Absence Of Amino Acids Research Articles

Comparative analysis of the adsorption properties of a carbon sorbent modified with sulfosalicylic acid solutions in the presence and absence of amino acids

The adsorption properties of a carbon sorbent in relation to sulfosalicylic acid in an individual solution and with an added amino acid (arginine or phenylalanine) were determined. It has been shown that the addition of arginine to an aqueous solution of sulfosalicylic acid leads to an increase in the amount of sulfosalicylic acid adsorbed on the carbon sorbent. The sorbents modified in the presence of amino acids showed high adsorption capacity for the methylene blue dye.

GATOR1 Mutations Impair PI3 Kinase-Dependent Growth Factor Signaling Regulation of mTORC1.

GATOR1 (GAP Activity TOward Rag 1) is an evolutionarily conserved GTPase-activating protein complex that controls the activity of mTORC1 (mammalian Target Of Rapamycin Complex 1) in response to amino acid availability in cells. Genetic mutations in the GATOR1 subunits, NPRL2 (nitrogen permease regulator-like 2), NPRL3 (nitrogen permease regulator-like 3), and DEPDC5 (DEP domain containing 5), have been associated with epilepsy in humans; however, the specific effects of these mutations on GATOR1 function and mTORC1 regulation are not well understood. Herein, we report that epilepsy-linked mutations in the NPRL2 subunit of GATOR1, NPRL2-L105P, -T110S, and -D214H, increase basal mTORC1 signal transduction in cells. Notably, we show that NPRL2-L105P is a loss-of-function mutation that disrupts protein interactions with NPRL3 and DEPDC5, impairing GATOR1 complex assembly and resulting in high mTORC1 activity even under conditions of amino acid deprivation. Furthermore, our studies reveal that the GATOR1 complex is necessary for the rapid and robust inhibition of mTORC1 in response to growth factor withdrawal or pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K). In the absence of the GATOR1 complex, cells are refractory to PI3K-dependent inhibition of mTORC1, permitting sustained translation and restricting the nuclear localization of TFEB, a transcription factor regulated by mTORC1. Collectively, our results show that epilepsy-linked mutations in NPRL2 can block GATOR1 complex assembly and restrict the appropriate regulation of mTORC1 by canonical PI3K-dependent growth factor signaling in the presence or absence of amino acids.

Phytochemical Profiling and Therapeutic Potential of Abelmoschus esculentus Fruit Extracts: Insights Into Antidiabetic Potential in In Vitro and In Vivo Experiments

Due to inadequate treatment, diabetes mellitus, which is characterized by hyperglycemia, is a global health challenge that requires creative management techniques. This study explores the therapeutic potential of Abelmoschus esculentus L. Moench fruit extracts in diabetes, offering an ample approach includes phytochemical analysis, qualitative and quantitative assessments, antidiabetic efficacy, antioxidant potential, and in vivo and in vitro investigations. Thin‐layer chromatography (TLC), high‐performance liquid chromatography (HPLC), and gas chromatography–mass spectrometry (GC–MS) were utilized to disclose the phytochemical profile of the fruit extracts, which indicated a diverse range of bioactive compounds. Four polyphenolic compounds including chlorogenic acid, quercetin, rutin, and morin were confirmed by HPLC fingerprinting, with rutin being the most prevalent. Qualitative analysis reveals the presence of carbohydrates, emodin, terpenoids, lignin, glycosides, and anthraquinones, while indicating the absence of amino acids, anthocyanins, phlobatannins, lactones, and leucoanthocyanins. Quantitative analysis reveals total phenolic, tannin, and flavonoid. In vitro assessments demonstrate the ability of the extracts to inhibit alpha amylase. Radical scavenging activities were evaluated through DPPH assay, underscoring their antioxidant capacity with high effect in methanol extracts. Additionally, the methanol extract decreased the blood glucose level of Type 2 diabetic mice. Notably, test samples stabilized blood glucose levels, reversed deviations in blood profile parameters, blood biochemistry, and regulated organ weight. Based on its antioxidant and antidiabetic effects, as well as positive effects on the physiology of Type 2 diabetic mice, A. esculentus emerges as an important nutraceutical vegetable. As an important nutraceutical vegetable, it holds promise for diabetes management. A. esculentus can be incorporated into dietary interventions for individuals with diabetes, harnessing its natural antioxidant and antidiabetic properties. Our findings validate the traditional use of A. esculentus in green therapeutics. In conclusion, A. esculentus emerges as a valuable ally in the fight against diabetes, bridging the gap between ancient wisdom and modern science. Further research and practical implementation are warranted to fully realize its potential.

VWCE modulates amino acid-dependent mTOR signaling and coordinates with KICSTOR to recruit GATOR1 to the lysosomes

The mechanistic target of rapamycin complex 1 (mTORC1) is a crucial regulator of cell growth. It senses nutrient signals and adjusts cellular metabolism accordingly. Deregulation of mTORC1 has been associated with metabolic diseases, cancer, and aging. Amino acid signals are transduced to mTORC1 through sensor proteins and two protein complexes named GATOR1 and GATOR2. In this study, we identify VWCE (von Willebrand factor C and EGF domains) as a negative regulator of amino acid-dependent mTORC1 signaling. Knockdown of VWCE promotes mTORC1 activity even in the absence of amino acids. VWCE interacts with the KICSTOR complex to facilitate the recruitment of GATOR1 to the lysosomes. Bioinformatic analysis reveals that expression of VWCE is reduced in prostate cancer. More importantly, overexpression of VWCE inhibits the development of prostate cancer. Therefore, VWCE may serve as a potential therapeutic target for the treatment of prostate cancers.

Redundant electrostatic interactions between GATOR1 and the Rag GTPase heterodimer drive efficient amino acid sensing in human cells

Cells need to coordinate nutrient availability with their growth and proliferation. In eukaryotic cells, this coordination is mediated by the mechanistic target of the rapamycin complex 1 (mTORC1) pathway. mTORC1 activation is regulated by two GTPase units, the Rag GTPase heterodimer and the Rheb GTPase. The RagA-RagC heterodimer controls the subcellular localization of mTORC1, and its nucleotide loading states are strictly controlled by upstream regulators including amino acid sensors. A critical negative regulator of the Rag GTPase heterodimer is GATOR1. In the absence of amino acids, GATOR1 stimulates GTP hydrolysis by the RagA subunit to turn off mTORC1 signaling. Despite the enzymatic specificity of GATOR1 to RagA, a recent cryo-EM structural model of the human GATOR1-Rag-Ragulator complex reveals an unexpected interface between Depdc5, a subunit of GATOR1, and RagC. Currently, there is no functional characterization of this interface, nor do we know its biological relevance. Here, combining structure-function analysis, enzymatic kinetic measurements, and cell-based signaling assays, we identified a critical electrostatic interaction between Depdc5 and RagC. This interaction is mediated by the positively charged Arg-1407 residue on Depdc5 and a patch of negatively charged residues on the lateral side of RagC. Abrogating this interaction impairs the GAP activity of GATOR1 and cellular response to amino acid withdrawal. Our results reveal how GATOR1 coordinates the nucleotide loading states of the Rag GTPase heterodimer, and thus precisely controls cellular behavior in the absence of amino acids.

Amino acids can deplete ATP and impair nitric oxide detoxification by Escherichia coli

Nitric oxide (·NO) is a prevalent antimicrobial that is known to damage iron-containing enzymes in amino acid (AA) biosynthesis pathways. With Escherichia coli, ·NO is detoxified in aerobic environments by Hmp, which is an enzyme that is synthesized de novo in response to ·NO. With this knowledgebase, it is expected that the availability of AAs in the extracellular environment would enhance ·NO detoxification, because AAs would foster translation of Hmp. However, we observed that ·NO detoxification by E. coli was far slower in populations grown and treated in the presence of AAs (AA+) in comparison to those grown and stressed in the absence of AAs (AA-). Further experiments revealed that AA+ populations had difficulty translating proteins under ·NO stress, and that ·NO activated the stringent response in AA+ populations. Additional work revealed significant ATP depletion in ·NO-stressed AA+ cultures that far exceeded that of ·NO-stressed AA- populations. Transcription, translation, and RelA were not found to be significant contributors to the ATP depletion observed, whereas AA import was implicated as a significant ATP consumption pathway. Alleviating ATP depletion while maintaining access to AAs partially restored ·NO detoxification, which suggested that ATP depletion contributed to the translational difficulties observed in ·NO-stressed AA+ populations. These data reveal an unexpected interaction within the ·NO response network of E. coli that stimulates a stringent response by RelA in conditions where AAs are plentiful.

Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle.

Malnutrition is implicated in human metabolic disorders, including hepatic steatosis and myosteatosis. The corresponding nutrient signals and sensors as well as signalling pathways have not yet been well studied. This study aimed to unravel the nutrient-sensing mechanisms in the pathogenesis of steatosis. Plin2, a lipid droplet (LD) protein-inhibiting lipolysis, is associated with steatosis in liver and muscle. Taking advantage of the Gal4-UAS system, we used the Drosophila melanogaster wing imaginal disc as an in vivo model to study the regulation of Plin2 proteostasis and LD homeostasis. Drosophila Schneider 2 (S2) cells were used for western blotting, immunoprecipitation assays, amino acid-binding assays and ubiquitination assays to further investigate the regulatory mechanisms of Plin2 in response to nutrient signals. Mouse AML12 hepatocytes, human JHH-7 and SNU-475 hepatoma cells were used for immunofluorescence, western blotting and immunoprecipitation to demonstrate that the mode of Plin2 regulation is evolutionarily conserved. In addition, we purified proteins from HEK293 cells and reconstituted in vitro cell-free systems in amino acid-binding assays, pulldown assays and ubiquitination assays to directly demonstrate the molecular mechanism by which Ubr1 senses amino acids to regulate Plin2 proteostasis. As a lipolysis inhibitor, Plin2 was significantly elevated in liver (P<0.05) and muscle (P<0.05) in patients with steatosis. Consistently, we found that the ubiquitin moiety can be conjugated to any Lys residue in Plin2, ensuring robust clearance of Plin2 by protein degradation. We further demonstrated that the E3 ubiquitin ligase Ubr1 targets Plin2 for degradation in an amino acid-dependent manner. Ubr1 uses two canonical substrate-binding pockets, independent of each other, to bind basic and bulky hydrophobic amino acids, respectively. Mechanistically, amino acid binding allosterically activates Ubr1 by alleviating Ubr1's auto-inhibition. In the absence of amino acids, or when the amino acid-binding capacity of Ubr1 is diminished, Ubr1-mediated Plin2 degradation is inactivated, leading to steatosis. We identified Ubr1 as an amino acid sensor regulating Plin2 proteostasis, bridging the knowledge gap between steatosis and nutrient sensing. Our work may provide new strategies for the prevention and treatment of steatosis.

Study on the Effects of Biologically Active Amino Acids on the Micellization of Anionic Surfactant Sodium Dodecyl Sulfate (SDS) at Different Temperatures

The micellar properties of the anionic surfactant, sodium dodecyl sulfate (SDS) are modified by the biologically active amino acids. Amino acids (AAs) have experienced a variety of interactions and are proposed to influence SDS micelles due to their nominated hydrophobic interactions. The present study determines the critical micellar concentration (CMC) of SDS in aqueous solutions as well as in amino aqueous solutions. Three amino acids (glutamic acid, histidine, and tryptophan) are considered here. The conductometric measurements were carried out using a wide range of SDS concentrations at different temperatures. Surface tension experiments have also been applied to estimate many surface parameters including surface excess concentration (Γmax), surface occupied area per surfactant molecule (Amin), surface tension at CMC (γcmc), surface pressure at CMC (Πcmc) and Gibbs free energy of adsorption (∆Gads°), enthalpy ∆Hm° and the critical packing parameter (CPP). Interestingly, CMC values of SDS in water and in aqueous amino acids estimated by the surface tension method are comparable with the corresponding values obtained by the conductance method. The thermodynamic parameters of SDS micellization were also evaluated in both presence and absence of AAs. The additives of AAs work to reduce the CMC values, as well as the SDS thermodynamic parameters. This reduction is highly dependent on the hydrophobicity of the AA side chain. Negative values of ∆Gm°, ∆Hm° elucidate that micellization of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. The outcomes here might be utilized for pharmaceutical applications to stabilize proteins and inhibit protein aggregation.

DRAM-4 and DRAM-5 are compensatory regulators of autophagy and cell survival in nutrient-deprived conditions.

Macroautophagy is a membrane‐trafficking process that delivers cytoplasmic material to lysosomes for degradation. The process preserves cellular integrity by removing damaged cellular constituents and can promote cell survival by providing substrates for energy production during hiatuses of nutrient availability. The process is also highly responsive to other forms of cellular stress. For example, DNA damage can induce autophagy and this involves up‐regulation of the Damage‐Regulated Autophagy Modulator‐1 (DRAM‐1) by the tumor suppressor p53. DRAM‐1 belongs to an evolutionarily conserved protein family, which has five members in humans and we describe here the initial characterization of two members of this family, which we term DRAM‐4 and DRAM‐5 for DRAM‐Related/Associated Member 4/5. We show that the genes encoding these proteins are not regulated by p53, but instead are induced by nutrient deprivation. Similar to other DRAM family proteins, however, DRAM‐4 principally localizes to endosomes and DRAM‐5 to the plasma membrane and both modulate autophagy flux when over‐expressed. Deletion of DRAM‐4 using CRISPR/Cas‐9 also increased autophagy flux, but we found that DRAM‐4 and DRAM‐5 undergo compensatory regulation, such that deletion of DRAM‐4 does not affect autophagy flux in the absence of DRAM‐5. Similarly, deletion of DRAM‐4 also promotes cell survival following growth of cells in the absence of amino acids, serum, or glucose, but this effect is also impacted by the absence of DRAM‐5. In summary, DRAM‐4 and DRAM‐5 are nutrient‐responsive members of the DRAM family that exhibit interconnected roles in the regulation of autophagy and cell survival under nutrient‐deprived conditions.

Antioxidant and Hepatoprotective Activity of Aerides odorata Lour. on Alcohol Induced Liver Damage in Rats

Natural products have been playing a vital role in protection against different diseases since ancient times. Many medicinal plants are still unexplored about their medicinal values scientifically, but they are still used in traditional medicine. The current study was aimed to explore and evaluate the phytochemical constituents, antioxidant activity against different free radicals with in vitro methods and in vivo methods using albino Wistar rats and hepatoprotective activity against ethanol-induced liver toxicity. The extracts of Aerides odorata show sterols, terpenoids, glycosides, saponins, flavonoids, tannins, phenols, alkaloids, quinones and the absence of amino acids and oils. The hydroalcoholic extract had showed presence of more phenolic and alkaloid contents compared to ethyl acetate and hexane extracts of Aerides odorata. The extracts of Aerides odorata had shown antioxidant potentiality in both in vitro and in vivo studies. The extracts had more inhibition in reducing 2,2-diphenyl-1-picrylhydrazyl and almost the same potentiality in altering antioxidant enzymes levels. The extracts of Aerides odorata had shown concentration-dependent hepatoprotective activity. However, it is moderate as compared with the standard drug Liv 52. The hydroalcoholic extracts had more activity compared to ethyl acetate extract. The activity is more in the reduction of free radicals but is lower in the reduction of hepatoprotection. The compound in Aerides odorata may act synergistically or individually in controlling both activities. Further studies are worthful in the evaluation of different biological activities and the isolation of individual bioactive compounds.

Activation of IRE1, PERK and salt-inducible kinases leads to Sec body formation in Drosophila S2 cells.

ABSTRACTThe phase separation of the non-membrane bound Sec bodies occurs in Drosophila S2 cells by coalescence of components of the endoplasmic reticulum (ER) exit sites under the stress of amino acid starvation. Here, we address which signaling pathways cause Sec body formation and find that two pathways are critical. The first is the activation of the salt-inducible kinases (SIKs; SIK2 and SIK3) by Na+ stress, which, when it is strong, is sufficient. The second is activation of IRE1 and PERK (also known as PEK in flies) downstream of ER stress induced by the absence of amino acids, which needs to be combined with moderate salt stress to induce Sec body formation. SIK, and IRE1 and PERK activation appear to potentiate each other through the stimulation of the unfolded protein response, a key parameter in Sec body formation. This work shows the role of SIKs in phase transition and re-enforces the role of IRE1 and PERK as a metabolic sensor for the level of circulating amino acids and salt. This article has an associated First Person interview with the first author of the paper.

Identification of amino acid response element of SLC38A9 as an ATF4-binding site in porcine skeletal muscle cells

Amino acids can affect protein synthesis by activating mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Amino acid transporters SLC38A9 on the lysosomal membrane not only transport amino acids, but also can sense amino acids and activate mTORC1 signaling pathway. Activating transcription factor 4 (ATF4) can promote the expression of amino acid transporters by binding with amino acid response element (AARE). In this study, two AAREs were found in the SLC38A9 promoter region of pig, and both of them bound to ATF4. The AARE in the first intron was located in the core promoter region of SLC38A9. ATF4 regulated mRNA expression level of SLC38A9 in porcine skeletal muscle cells. In the absence of amino acids, the expression of ATF4 decreased and the expression of SLC38A9 increased. After leucine addition, the expression levels of ATF4 and SLC38A9 increased. It suggested that in the absence of amino acids, the expression of SLC38A9 was increased via binding of ATF4 to AARE binding factors in SLC38A9 promoter fragment; after the addition of leucine, ATF4 was activated, resulting in the increase of SLC38A9 expression.

ArfGAP1 inhibits mTORC1 lysosomal localization and activation

The mammalian target of rapamycin complex 1 (mTORC1) integrates nutrients, growth factors, stress, and energy status to regulate cell growth and metabolism. Amino acids promote mTORC1 lysosomal localization and subsequent activation. However, the subcellular location or interacting proteins of mTORC1 under amino acid‐deficient conditions is not completely understood. Here, we identify ADP‐ribosylation factor GTPase‐activating protein 1 (ArfGAP1) as a crucial regulator of mTORC1. ArfGAP1 interacts with mTORC1 in the absence of amino acids and inhibits mTORC1 lysosomal localization and activation. Mechanistically, the membrane curvature‐sensing amphipathic lipid packing sensor (ALPS) motifs that bind to vesicle membranes are crucial for ArfGAP1 to interact with and regulate mTORC1 activity. Importantly, ArfGAP1 represses cell growth through mTORC1 and is an independent prognostic factor for the overall survival of pancreatic cancer patients. Our study identifies ArfGAP1 as a critical regulator of mTORC1 that functions by preventing the lysosomal transport and activation of mTORC1, with potential for cancer therapeutics.

Bioactivity evaluation of amino acid-conjugates with protein versus cellulose based conjugates and extracted flavonoids

The work in this article was done to evaluate the performance of new protein-based bioactive compounds for treating the cancer cells. These bioactive compounds were synthesized by condensation reaction of sodium caseinate with amino acids in absence of solvent and evidenced by FTIR, TGA and DSC analyses. The bioactivity of these protein-based conjugates (SC-conjugates), was evaluated towards different cancer cell lines such as Breast MCF7, Colon HCT116, Lung A549 and Human hepatocellular carcinoma HePG2) in comparison with sodium carboxymethyl cellulose-amino acid SCMC-conjugates. Two types of amino acids (phenylalanine and methionine) were used to evaluate the role of phenyl group contained in the amino acid on bioactivity performance. The effective role and safety behavior of the conjugates were assessed from the values of selectivity index against RPE1 [normal retina cell line], moreover their cancer inhibition versus natural extracted flavonoids whether individually or in hybrid.The results showed the effective performance of SC-PA conjugate in inhibiting the cancer cell proliferation, of most examined cancer cell lines, especially against breast cancer MCF7 and colon HCT116 (IC50 and IC90 are 39.8–44.1 μg/mL and 71.7–83.6 μg/mL, respectively). IC50 of this conjugate for MCF7 was equivalent to Rutin natural flavonoid. The Rutin has synergistic inhibition effect to MCF7 when it used in hybrid with SC-PA, at which it leads to decrease the IC50 from 39.8 to 33.1 μg/mL.

Structure-seq2 probing of RNA structure upon amino acid starvation reveals both known and novel RNA switches in Bacillus subtilis.

RNA structure influences numerous processes in all organisms. In bacteria, these processes include transcription termination and attenuation, small RNA and protein binding, translation initiation, and mRNA stability, and can be regulated via metabolite availability and other stresses. Here we use Structure-seq2 to probe the in vivo RNA structurome of Bacillus subtilis grown in the presence and absence of amino acids. Our results reveal that amino acid starvation results in lower overall dimethyl sulfate (DMS) reactivity of the transcriptome, indicating enhanced protection owing to protein binding or RNA structure. Starvation-induced changes in DMS reactivity correlated inversely with transcript abundance changes. This correlation was particularly pronounced in genes associated with the stringent response and CodY regulons, which are involved in adaptation to nutritional stress, suggesting that RNA structure contributes to transcript abundance change in regulons involved in amino acid metabolism. Structure-seq2 accurately reported on four known amino acid-responsive riboswitches: T-box, SAM, glycine, and lysine riboswitches. Additionally, we discovered a transcription attenuation mechanism that reduces yfmG expression when amino acids are added to the growth medium. We also found that translation of a leader peptide (YfmH) encoded just upstream of yfmG regulates yfmG expression. Our results are consistent with a model in which a slow rate of yfmH translation caused by limitation of the amino acids encoded in YfmH prevents transcription termination in the yfmG leader region by favoring formation of an overlapping antiterminator structure. This novel RNA switch offers a way to simultaneously monitor the levels of multiple amino acids.

Phytochemical Analysis and Anti-diabetic Potential of Annona muricata L., Persea americana Mill. and Montrichardia arborescens L. Schott Utilized by the Residents of Pakuri (St. Cuthbert’s Mission) in Guyana

Aim: This study was designed to assess the utilization of plants with anti-diabetic properties and to conduct preliminary phytochemical analysis and moreover, to assess the anti-diabetic potential of selected plants used to treat and manage Type 2 diabetes mellitus (T2DM) among the residents of Pakuri (St. Cuthbert’s Mission) in Guyana.&#x0D; Methodology: The leaves of sour sop (Annona muricata L.), pear (Persea americana Mill.) and Mocou-Mocou (Montrichardia arborescens L. Schott) underwent phytochemical testing and a-amylase Inhibition testing to determine their anti-diabetic properties.&#x0D; Results: This study showed that the leaves of pear, sour sop and mocou mocou contained different chemical constituents including alkaloids, flavonoids, saponins and tannins but the absence of amino acids (proteins), carbohydrates and glycosides. The a-amylase inhibitory studies performed demonstrated that the extracts of A. muricata in ethanol and chloroform had significant inhibitory potential. &#x0D; Conclusion: Considering the promising potential of phytochemicals and the anti-diabetic activity of these species of plant extracts in anti-diabetic drug development, in vivo experiments and clinical trials are required for efficacy and safety evaluation. Also, the anti-diabetic phytochemicals may be used in combination with existing orthodox drugs, thereby, reducing the dose of synthetic anti-diabetic drugs, which will help in addressing the toxicity and cost-related issues in chronic use during the management of diabetes mellitus (DM).

Phosphatidic acid drives mTORC1 lysosomal translocation in the absence of amino acids

Mammalian target of rapamycin complex 1 (mTORC1) promotes cell growth and proliferation in response to nutrients and growth factors. Amino acids induce lysosomal translocation of mTORC1 via the Rag GTPases. Growth factors activate Ras homolog enriched in brain (Rheb), which in turn activates mTORC1 at the lysosome. Amino acids and growth factors also induce the phospholipase D (PLD)-phosphatidic acid (PA) pathway, required for mTORC1 signaling through mechanisms that are not fully understood. Here, using human and murine cell lines, along with immunofluorescence, confocal microscopy, endocytosis, PLD activity, and cell viability assays, we show that exogenously supplied PA vesicles deliver mTORC1 to the lysosome in the absence of amino acids, Rag GTPases, growth factors, and Rheb. Of note, pharmacological or genetic inhibition of endogenous PLD prevented mTORC1 lysosomal translocation. We observed that precancerous cells with constitutive Rheb activation through loss of tuberous sclerosis complex subunit 2 (TSC2) exploit the PLD-PA pathway and thereby sustain mTORC1 activation at the lysosome in the absence of amino acids. Our findings indicate that sequential inputs from amino acids and growth factors trigger PA production required for mTORC1 translocation and activation at the lysosome.

Thermodynamic and kinetic insights into the role of amino acids in improving the adhesion of iota-carrageenan as a natural corrosion inhibitor to the aluminum surface

The effect of amino acids on improving the corrosion inhibition performance of i-carrageenan through increasing the polymer adhesion to the aluminum surface in 2 M HCl solution was evaluated by using weight loss measurements at temperatures ranging from 25°C to 45°C. The studied amino acids, including Glycine, Alanine, Isoleucine, Serine, and Cysteine, are believed to play an adsorption mediating role to reach a coherent protection layer on the metal surface. The obtained weight loss data are used to calculate the activation parameters of the transition state formation (Ea, and ) to explain the mechanism of inhibition. A thermodynamic insight into the adsorption phenomenon of the inhibitor on the aluminum surface in the presence and absence of amino acids is provided by calculating the standard Gibbs free energy (), enthalpy (), and entropy () of the adsorption process. The results show a significant enhancement in the inhibition efficiency of i-carrageenan in the presence of amino acids. The obtained values are negative and become more negative with the addition of amino acid to the medium. This indicates that the inhibitor adsorption on the metal surface has a spontaneous nature, and this spontaneity increases in the presence of amino acids. It is also found that the adsorption process of i-carrageenan in the presence of amino acids is driven by a change in entropy, whereas it is controlled by changes in both enthalpy and entropy in the absence of amino acids.

Effects of the presence and absence of amino acids on translation, signaling, and long-term depression in hippocampal slices from Fmr1 knockout mice.

Fragile X syndrome (FXS) is caused by silencing of the FMR1 gene and consequent absence of its protein product, fragile X mental retardation protein (FMRP). FMRP is an RNA-binding protein that can suppress translation. The absence of FMRP leads to symptoms of FXS including intellectual disability and has been proposed to lead to abnormalities in synaptic plasticity. Synaptic plasticity, protein synthesis, and cellular growth pathways have been studied extensively in hippocampal slices from a mouse model of FXS (Fmr1 KO). Enhanced metabotropic glutamate receptor 5 (mGluR5)-dependent long-term depression (LTD), increased rates of protein synthesis, and effects on signaling molecules have been reported. These phenotypes were found under amino acid starvation, a condition that has widespread, powerful effects on activation and translation of proteins involved in regulating protein synthesis. We asked if this non-physiological condition could have effects on Fmr1 KO phenotypes reported in hippocampal slices. We performed hippocampal slice experiments in the presence and absence of amino acids. We measured rates of incorporation of a radiolabeled amino acid into protein to determine protein synthesis rates. By means of western blots, we assessed relative levels of total and phosphorylated forms of proteins involved in signaling pathways regulating translation. We measured evoked field potentials in area CA1 to assess the strength of the long-term depression response to mGluR activation. In the absence of amino acids, we replicate many of the reported findings in Fmr1 KO hippocampal slices, but in the more physiological condition of inclusion of amino acids in the medium, we did not find evidence of enhanced mGluR5-dependent LTD. Activation of mGluR5 increased protein synthesis in both wild type and Fmr1 KO. Moreover, mGluR5 activation increased eIF2α phosphorylation and decreased phosphorylation of p70S6k in slices from Fmr1 KO. We propose that the eIF2α response is a cellular attempt to compensate for the lack of regulation of translation by FMRP. Our findings call for a re-examination of the mGluR theory of FXS.

Turning on a G protein receptor

Signal Transduction The mammalian target of rapamycin complex 1 (mTORC1) protein kinase is activated at the lysosomal membrane and helps control autophagy and metabolism. It interacts with other proteins that act as sensors for stimuli like amino acids. Gan et al. used an unbiased screen to discover another protein that functions in this complex, one with similarity to heterotrimeric G protein—coupled receptors (GPCRs). The GPCR-like protein, GPR137B, appears to regulate cycles of association and release of the small guanosine triphosphatase Rag and mTORC1 at the lysosome even in the absence of amino acids. Whether a ligand for the orphan receptor could provide additional regulation adds a further intriguing twist. Nat. Cell Biol. 22 , 614 (2019).