Naturally occurring organic osmolytes: From cell physiology to disease prevention

Insights into the dynamic interactions of RNase a and osmolytes through computational approaches

Osmolytes are small organic molecules that are known to stabilize proteins and other biological macromolecules under various stressful conditions. They belong to various categories such as amino acids, methylamines, and polyols. These substances are commonly known as 'compatible solutes' because they do not disrupt cellular processes and help regulate the osmotic balance within cells. In the case of ribonuclease A (RNase A), which is prone to aggregation, the presence of osmolytes can help to maintain its structural stability and prevent unwanted interactions leading to protein aggregation. In this study, we investigated the interaction between RNase A and several osmolytes using molecular docking and molecular dynamics (MD) simulations. We performed molecular docking to predict the binding mode and binding affinity of each osmolyte with RNase A. MD simulations were then carried out to investigate the dynamics and stability of the RNase A-osmolyte complexes. Our results show that two osmolytes, glucosylglycerol and sucrose have favorable binding affinities with RNase A. The possible role of these osmolytes in stabilizing the RNase A and prevention of aggregation is also explored. By providing computational insights into the interaction between RNase A and osmolytes, the study offers valuable information that could aid in comprehending the mechanisms by which osmolytes protect proteins and help in designing therapeutics for protein-related disorders based on osmolytes. These findings may have significant implications for the development of novel strategies aimed at preventing protein misfolding and aggregation in diverse disease conditions.Communicated by Ramaswamy H. Sarma.

Escherichia coli as a versatile cell factory: Advances and challenges in recombinant protein production

E. coli plays a substantial role in recombinant protein production. Its importance increased with the discovery of recombinant DNA technology and the subsequent production of the first recombinant insulin in E. coli. E. coli is a widely used and cost-effective host to produce recombinant proteins. It is also noteworthy that a significant portion of the approved therapeutic proteins have been produced in this organism. Despite these advantages, it has some disadvantages, such as toxicity and lack of eukaryotic post-translational modifications that can lead to the production of misfolded, insoluble, or dysfunctional proteins. This study focused on the challenges and engineering approaches for improved expression and solubility in recombinant protein production in E. coli. In this context, solution strategies such as strain and vector selection, codon usage, mRNA stability, expression conditions, translocation to the periplasmic region and addition of fusion tags in E. coli were discussed.

Phenylalanine as an effective stabilizer and aggregation inhibitor of Bacillus amyloliquefaciens alpha-amylase

Aromatic compounds are known anti-amyloid aggregates. Their effect on amorphous aggregates of proteins is, however, less studied. We chose aromatic amino acids Trp, Tyr, and Phe, as well as another known stabilizer (i.e. Arg), as potential compatible solvents to be tested on Bacillus amyloliquefaciens alpha-amylase (BAA). Among these additives, Phe was the only one to be effective on the thermal inactivation and amorphous aggregation of BAA, while preserving its intrinsic activity. A concentration of 50 mM Phe was used to test its potential in counteracting the deleterious effect of BAA amorphous aggregates in vivo. After 21 days of daily subcutaneous injections of the native enzyme to mice, amorphous aggregates of BAA, as well as aggregates produced in presence of 50 mM Phe, the tissues located at the site of injection were studied histologically. Amorphous aggregates caused an increase in macrophages and lipid droplets. Serum levels of IL6 and TNF-α were also accordingly elevated and indicative of an inflammation state. Aggregates also resulted into increased levels of glucose, triglycerides and cholesterol, as well as liver enzymes SGOT and SGPT. On the other hand, the presence of Phe prevented this exacerbated inflammatory state and the subsequent impairment of biochemical parameters. In conclusion, Phe is an interesting compound for both stabilizing proteins and counteracting the pathological effect of amorphous aggregates.

Effects of osmolytes under crowding conditions on the properties of muscle glycogen phosphorylase b

The study of the relationship between the activity and stability of enzymes under crowding conditions in the presence of osmolytes is important for understanding the functioning of a living cell. The effect of osmolytes (trehalose and betaine) on the secondary and tertiary structure and activity of muscle glycogen phosphorylase b (Phb) under crowding conditions created by PEG 2000 and PEG 20000 was investigated using dynamic light scattering, differential scanning calorimetry, circular dichroism spectroscopy, fluorimetry and enzymatic activity assay. At 25 °C PEGs increased Phb activity, but PEG 20000 to a greater extent. Wherein, PEG 20000 significantly destabilized its tertiary and secondary structure, in contrast to PEG 2000. Trehalose removed the effects of PEGs on Phb, while betaine significantly reduced the activating effect of PEG 20000 without affecting the action of PEG 2000. Under heat stress at 48 °C, the protective effect of osmolytes under crowding conditions was more pronounced than at room temperature, and the Phb activity in the presence of osmolytes was higher in these conditions than in diluted solutions. These results provide important insights into the complex mechanism, by which osmolytes affect the structure and activity of Phb under crowding conditions.

Inhibitors of amyloid fibril formation

Many diseases are caused by misfolded and denatured proteins, leading to neurodegenerative diseases. In recent decades researchers have developed a variety of compounds, including polymeric inhibitors and natural compounds, antibodies, and chaperones, to inhibit protein aggregation, decrease the toxic effects of amyloid fibrils, and facilitate refolding proteins. The causes and mechanisms of amyloid formation are still unclear, and there are no effective treatments for Amyloid diseases. This section describes research and achievements in the field of inhibiting amyloid accumulation and also discusses the importance of various strategies in facilitating the removal of aggregates species (refolding) in the treatment of neurological diseases such as chemical methods like as, small molecules, metal chelators, polymeric inhibitors, and nanomaterials, as well as the use of biomolecules (peptide and, protein, nucleic acid, and saccharide) as amyloid inhibitors, are also highlighted.

Metabolomic profiling of the nutritional components of chicory leaves following heat processing

Chicory (Cichorium intybus L.; witloof) is a crisp bitter leafy vegetable, popularly used in western cuisine in salads and soups (leaves) and as an alternative to coffee (roasted roots). In this study, we explored the effect of heat processing under various temperatures and for different durations on the nutritional composition of chicory leaves using gas chromatography-mass spectrometry (GC/MS) and principal component analysis (PCA). "Vintor" chicory leaves were processed and homogenized to obtain lyophilized samples, and their moisture content and pH were measured. Heat processing was conducted at 4, 30, 60, and 100°C. Metabolites were extracted and analyzed using GC/MS. The results were statistically analyzed using multiple t-tests and Tukey-Kramer method. A PCA was conducted using standardized data. A lower temperature (≤60°C) positively influenced the concentrations of nutritional components (sugars, free amino acids, and organic acids), branched-chain amino acids (which reportedly improve exercise performance), and γ-aminobutyric acid (which exerts antihypertensive effects). Whereas, a higher temperature (100°C) and microwave processing induced the generation of low-molecular-weight sugars from polysaccharides and glycosides, decreased free amino acid concentrations, and caused heat-induced aminocarbonyl reactions. This study provides valuable information for enhancing the flavor profiles and potential health benefits of chicory leaves by identifying the optimal heat processing parameters for preserving the desired nutritional value. PRACTICAL APPLICATION: The palatability, nutritional content, and health benefits of chicory have been evaluated based on its inherent constituents, but changes in these parameters during food processing remain unclear. Heating at 30 and 60°C activated secondary metabolism in chicory, increasing the amino acid and organic acid concentrations, whereas heating at 100°C and microwave processing increased the sugar concentrations in chicory. Thus, the nutritional value and potential health benefits of chicory could be enhanced by processing it under controlled temperatures; the findings are valuable for both consumers and food processing industry.

Widespread Peptide Surfactants with Post-translational C-methylations Promote Bacterial Development

Bacteria produce a variety of peptides to mediate nutrient acquisition, microbial interactions, and other physiological processes. Of special interest are surface-active peptides that aid in growth and development. Herein, we report the structure and characterization of clavusporins, unusual and hydrophobic ribosomal peptides with multiple C-methylations at unactivated carbon centers, which help drastically reduce the surface tension of water and thereby aid in Streptomyces development. The peptides are synthesized by a previously uncharacterized protein superfamily, termed DUF5825, in conjunction with a vitamin B12-dependent radical S-adenosylmethionine metalloenzyme. The operon encoding clavusporin is wide-spread among actinomycete bacteria, suggesting a prevalent role for clavusporins as morphogens in erecting aerial hyphae and thereby advancing sporulation and proliferation.

Effect of Chemical Chaperones on the Stability of Proteins during Heat- or Freeze-Thaw Stress

The importance of studying the structural stability of proteins is determined by the structure-function relationship. Protein stability is influenced by many factors among which are freeze-thaw and thermal stresses. The effect of trehalose, betaine, sorbitol and 2-hydroxypropyl-β-cyclodextrin (HPCD) on the stability and aggregation of bovine liver glutamate dehydrogenase (GDH) upon heating at 50 °C or freeze-thawing was studied by dynamic light scattering, differential scanning calorimetry, analytical ultracentrifugation and circular dichroism spectroscopy. A freeze-thaw cycle resulted in the complete loss of the secondary and tertiary structure, and aggregation of GDH. All the cosolutes suppressed freeze-thaw- and heat-induced aggregation of GDH and increased the protein thermal stability. The effective concentrations of the cosolutes during freeze-thawing were lower than during heating. Sorbitol exhibited the highest anti-aggregation activity under freeze-thaw stress, whereas the most effective agents stabilizing the tertiary structure of GDH were HPCD and betaine. HPCD and trehalose were the most effective agents suppressing GDH thermal aggregation. All the chemical chaperones stabilized various soluble oligomeric forms of GDH against both types of stress. The data on GDH were compared with the effects of the same cosolutes on glycogen phosphorylase b during thermal and freeze-thaw-induced aggregation. This research can find further application in biotechnology and pharmaceutics.

Osmolytes: Wonder molecules to combat protein misfolding against stress conditions

The proper functioning of any protein depends on its three dimensional conformation which is achieved by the accurate folding mechanism. Keeping away from the exposed stress conditions leads to cooperative unfolding and sometimes partial folding, forming the structures like protofibrils, fibrils, aggregates, oligomers, etc. leading to several neurodegenerative diseases like Parkinson's disease, Alzheimer's, Cystic fibrosis, Huntington, Marfan syndrome, and also cancers in some cases, too. Hydration of proteins is necessary, which may be achieved by the presence of organic solutes called osmolytes within the cell. Osmolytes belong to different classes in different organisms and play their role by preferential exclusion of osmolytes and preferential hydration of water molecules and achieves the osmotic balance in the cell otherwise it may cause problems like cellular infection, cell shrinkage leading to apoptosis and cell swelling which is also the major injury to the cell. Osmolyte interacts with protein, nucleic acids, intrinsically disordered proteins by non-covalent forces. Stabilizing osmolytes increases the Gibbs free energy of the unfolded protein and decreases that of folded protein and vice versa with denaturants (urea and guanidinium hydrochloride). The efficacy of each osmolyte with the protein is determined by the calculation of m value which reflects its efficiency with protein. Hence osmolytes can be therapeutically considered and used in drugs.

Transcriptomic Analysis of Heat Stress Response in Brassica rapa L. ssp. pekinensis with Improved Thermotolerance through Exogenous Glycine Betaine

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is sensitive to high temperature, which will cause the B. rapa to remain in a semi-dormancy state. Foliar spray of GB prior to heat stress was proven to enhance B. rapa thermotolerance. In order to understand the molecular mechanisms of GB-primed resistance or adaptation towards heat stress, we investigated the transcriptomes of GB-primed and non-primed heat-sensitive B. rapa ‘Beijing No. 3’ variety by RNA-Seq analysis. A total of 582 differentially expressed genes (DEGs) were identified from GB-primed plants exposed to heat stress relative to non-primed plants under heat stress and were assigned to 350 gene ontology (GO) pathways and 69 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. The analysis of the KEGG enrichment pathways revealed that the most abundantly up-regulated pathways were protein processing in endoplasmic reticulum (14 genes), followed by plant hormone signal transduction (12 genes), ribosome (8 genes), MAPK signaling pathway (8 genes), homologous recombination (7 genes), nucleotide excision repair metabolism (5 genes), glutathione metabolism (4 genes), and ascorbate and aldarate metabolism (4 genes). The most abundantly down-regulated pathways were plant-pathogen interaction (14 genes), followed by phenylpropanoid biosynthesis (7 genes); arginine and proline metabolism (6 genes); cutin, suberine, and wax biosynthesis (4 genes); and tryptophan metabolism (4 genes). Several calcium sensing/transducing proteins, as well as transcription factors associated with abscisic acid (ABA), salicylic acid (SA), auxin, and cytokinin hormones were either up- or down-regulated in GB-primed B. rapa plants under heat stress. In particular, expression of the genes for antioxidant defense, heat shock response, and DNA damage repair systems were highly increased by GB priming. On the other hand, many of the genes involved in the calcium sensors and cell surface receptors involved in plant innate immunity and the biosynthesis of secondary metabolites were down-regulated in the absence of pathogen elicitors in GB-primed B. rapa seedlings. Overall GB priming activated ABA and SA signaling pathways but deactivated auxin and cytokinin signaling pathways while suppressing the innate immunity in B. rapa seedlings exposed to heat stress. The present study provides a preliminary understanding of the thermotolerance mechanisms in GB-primed plants and is of great importance in developing thermotolerant B. rapa cultivars by using the identified DEGs through genetic modification.

The Effect of Chemical Chaperones on Proteins with Different Aggregation Kinetics

Formation and accumulation of protein aggregates adversely affect intracellular processes in living cells and are negative factors in the production and storage of protein preparations. Chemical chaperones can prevent protein aggregation, but this effect is not universal and depends on the target protein structure and kinetics of its aggregation. We studied the effect of betaine (Bet) and lysine (Lys) on thermal aggregation of muscle glycogen phosphorylase b (Phb) at 48°C (aggregation order, n = 0.5), UV-irradiated Phb (UV-Phb) at 37°C (n = 1), and apo-form of Phb (apo-Phb) at 37°C (n = 2). Using dynamic light scattering, differential scanning calorimetry, and analytical ultracentrifugation, we have shown that Bet protected Phb and apo-Phb from aggregation, but accelerated the aggregation of UV-Phb. At the same time, Lys prevented UV-Phb and apo-Phb aggregation, but increased the rate of Phb aggregation. The mechanisms of chemical chaperone action on the tertiary and quaternary structures and kinetics of thermal aggregation of the target proteins are discussed. Comparison of the effects of chemical chaperones on the proteins with different aggregation kinetics provides more complete information on the mechanism of their action.

Influence of stabilizing osmolytes on hen egg white lysozyme fibrillation

Communicated by Ramaswamy H. Sarma.

Polyamine pathways interconnect with GABA metabolic processes to mediate the low-temperature response in plants

Low temperatures are among the most commonly encountered environmental conditions that adversely affect plant growth and development, leading to substantial reductions in crop productivity. Plants have accordingly evolved coordinated mechanisms that confer low-temperature adaptation and resistance. The plant metabolic network, including polyamines (PAs) and γ-aminobutyric acid (GABA) is reprogrammed to ensure that essential metabolic homeostasis is maintained in response to cold stress conditions. Additionally, GABA might serve as a central molecule in the defense system during low-temperature tolerance in plants. However, our understanding of how these metabolites function in conferring cold tolerance is still far from complete. Here, we summarized how PAs and GABA function in conferring cold tolerance, and describe the crucial role of GABA in the mitigation of ROS during cold stress in plants.

Implications of trimethylamine N-oxide (TMAO) and Betaine in Human Health: Beyond Being Osmoprotective Compounds

Osmolytes are naturally occurring small molecular weight organic molecules, which are accumulated in large amounts in all life forms to maintain the stability of cellular proteins and hence preserve their functions during adverse environmental conditions. Trimethylamine N-oxide (TMAO) and N,N,N-trimethylglycine (betaine) are methylamine osmolytes that have been extensively studied for their diverse roles in humans and have demonstrated opposing relations with human health. These osmolytes are obtained from food and synthesized endogenously using dietary constituents like choline and carnitine. Especially, gut microbiota plays a vital role in TMAO synthesis and contributes significantly to plasma TMAO levels. The elevated plasma TMAO has been reported to be correlated with the pathogenesis of numerous human diseases, including cardiovascular disease, heart failure, kidney diseases, metabolic syndrome, etc.; Hence, TMAO has been recognized as a novel biomarker for the detection/prediction of several human diseases. In contrast, betaine acts as a methyl donor in one-carbon metabolism, maintains cellular S-adenosylmethionine levels, and protects the cells from the harmful effects of increased plasma homocysteine. Betaine also demonstrates antioxidant and anti-inflammatory activities and has a promising therapeutic value in several human diseases, including homocystinuria and fatty liver disease. The present review examines the multifarious functions of TMAO and betaine with possible molecular mechanisms towards a better understanding of their emerging and diverging functions with probable implications in the prevention, diagnosis, and treatment of human diseases.

Urea ameliorates trimethylamine N-oxide-Induced aggregation of intrinsically disordered α-casein protein: the other side of the urea-methylamine counteraction

Trimethylamine N-oxide (TMAO) is generally accumulated by organisms and cells to cope with denaturing effects of urea/hydrodynamic pressure on proteins and can even reverse misfolded or aggregated proteins so as to sustain proteostasis. However, most of the work regarding this urea-TMAO counteraction has been performed on folded proteins. Compelling evidence of aggregation of intrinsically disordered proteins (IDPs) like tau, α-synuclein, amyloid β etc., by TMAO and its potential to impact various protein processes in absence of stressing agents (such as urea) suggests that the contrary feature of interaction profiles of urea and TMAO maximizes their chances of offsetting the perturbing effects of each other. Recently, our lab observed that TMAO induces aggregation of α-casein, a model IDP. In this context, the present study, for the first time, evaluated urea for its potential to counteract the TMAO-induced aggregation of α-casein. It was observed that, at the biologically relevant ratios of 2:1 or 3:1 (urea:TMAO), urea was able to inhibit TMAO-induced aggregation of α-casein. However, urea did not reverse the effects of TMAO on α-casein. In addition to this, α-casein in presence of 1:1 and 2:1 urea:TMAO working ratios show aggregation-induced cytotoxic effect on HEK-293, Neuro2A and HCT-116 cell lines but not in presence of 3:1 working ratio, as there was no aggregation at all. The study infers that the accumulation of TMAO alone in the cells, in absence of stress (such as urea), might result in loss of conformational flexibility and aggregation of IDPs in TMAO accumulating organisms.Communicated by Ramaswamy H. Sarma.

Transcriptome expression profiles reveal response mechanisms to drought and drought-stress mitigation mechanisms by exogenous glycine betaine in maize

Drought stress is one of the major abiotic stresses that limit growth, development and yield of maize crops. To better understand the responses of maize inbred lines with different levels of drought resistance and the molecular mechanism of exogenous glycine betaine (GB) in alleviating drought stress, the responses of two maize inbred lines to drought stress and to the stress-mitigating effects of exogenous GB were investigated. Seedling morphology, physiological and biochemical indexes, root cell morphology and root transcriptome expression profiles were compared between a drought-tolerant inbred line Chang 7-2 and drought-sensitive inbred line TS141. Plants of both lines were subjected to treatments of drought stress alone and drought stress with application of exogenous GB. The results showed that with the increase of drought treatment time, the growth and development of TS141 were inhibited, while those of Chang 7-2 were not significantly different from those of the control (no drought stress and GB). Compared with the corresponding data of the drought-stress group, every index measured from the two inbred lines indicated mitigating effects from exogenous GB, and TS141 produced stronger mitigating responses due to the GB. Transcriptome analysis showed that 562 differentially expressed genes (DEGs) were up-regulated and 824 DEGs were down-regulated in both inbred lines under drought stress. Due to the exogenous GB, 1061 DEGs were up-regulated and 424 DEGs were down-regulated in both lines. In addition, quantitative real-time polymerase chain reaction (qRT-PCR) was used to verify 10 DEGs screened from the different treatments. These results showed that the expression of 9 DEGs were basically consistent with their respective transcriptome expression profiles. The results of this study provide models of potential mechanisms of drought tolerance in maize as well as potential mechanisms of how exogenous GB may regulate drought tolerance.

Metabolic Responses of "Big Six" Escherichia coli in Wheat Flour to Thermal Treatment Revealed by Nuclear Magnetic Resonance Spectroscopy

Escherichia coli outbreaks linked to wheat flour consumption have kept emerging in recent years, which necessitated an antimicrobial step being incorporated into the flour production process. The objectives of this in vivo study were to holistically evaluate the sanitizing efficacy of thermal treatment at 60 and 70°C against the "big six" E. coli strains (O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) in wheat flour and to assess the strain-specific metabolic responses using nuclear magnetic resonance (NMR) spectroscopy. The 70°C treatment temperature indiscriminatingly inactivated all strains by over 4.3-log CFU/g within 20 min, suggesting the high sanitization effectiveness of this treatment temperature, whereas the treatment at 60°C inactivated the strains to various degrees during the 1-h process. The most resistant strains at 60°C, O26 and O45, were characterized by amino acid and sugar depletion, and their high resistance was attributed to the dual effects of activated heat shock protein (HSP) synthesis and promoted glycolysis. O121 also demonstrated these metabolic changes, yet its thermal resistance was largely impaired by the weakened membrane structure and diminished osmotic protection due to phosphorylcholine exhaustion. In contrast, O111, O145, and O103 presented a substantial elevation of metabolites after stress at 60°C; their moderate thermal resistance was mainly explained by the accumulation of amino acids as osmolytes. Overall, the study enhanced our understanding of the metabolic responses of big six E. coli to heat stress and provided a model for conducting NMR-based metabolomic studies in powdered food matrices. IMPORTANCE "Big six" Escherichia coli strains have caused several outbreaks linked to wheat flour consumption in the last decade, revealing the vital importance of adopting an antimicrobial treatment during the flour production process. Therefore, the present study was carried out to evaluate the efficacy of a typical sanitizing approach, thermal treatment, against the big six strains in wheat flour along with the underlying antimicrobial mechanisms. Findings showed that thermal treatment at 60 and 70°C could markedly mitigate the loads of all strains in wheat flour. Moreover, activated heat shock protein synthesis combined with expedited glycolysis and enhanced osmotic protection were identified as two major metabolic alteration patterns in the E. coli strains to cope with the heat stress. With the responses of big six in wheat flour to thermal treatment elucidated, scientific basis for incorporating a thermal inactivation step in wheat flour production was provided.

Effect of Sorbitol on Alpha-Crystallin Structure and Function

Loss of eye lens transparency due to cataract is the leading cause of blindness all over the world. While aggregation of lens crystallins is the most common endpoint in various types of cataracts, chaperone-like activity (CLA) of α-crystallin preventing protein aggregation is considered to be important for maintaining the eye lens transparency. Osmotic stress due to increased accumulation of sorbitol under hyperglycemic conditions is believed to be one of the mechanisms for diabetic cataract. In addition, compromised CLA of α-crystallin in diabetic cataract has been reported. However, the effect of sorbitol on the structure and function of α-crystallin has not been elucidated yet. Hence, in the present exploratory study, we described the effect of varying concentrations of sorbitol on the structure and function of α-crystallin. Alpha-crystallin purified from the rat lens was incubated with varying concentrations of sorbitol in the dark under sterile conditions for up to 5 days. At the end of incubation, structural properties and CLA were evaluated by spectroscopic methods. Interestingly, different concentrations of sorbitol showed contrasting results: at lower concentrations (5 and 50 mM) there was a decrease in CLA and subtle alterations in secondary and tertiary structure but not at higher concentrations (500 mM). Though, these results shed a light on the effect of sorbitol on α-crystallin structure-function, further studies are required to understand the mechanism of the observed effects and their implication to cataractogenesis.

Interactions in Ternary Aqueous Solutions of NMA and Osmolytes-PARAFAC Decomposition of FTIR Spectra Series

Intermolecular interactions in aqueous solutions are crucial for virtually all processes in living cells. ATR-FTIR spectroscopy is a technique that allows changes caused by many types of such interactions to be registered; however, binary solutions are sometimes difficult to solve in these terms, while ternary solutions are even more difficult. Here, we present a method of data pretreatment that facilitates the use of the Parallel Factor Analysis (PARAFAC) decomposition of ternary solution spectra into parts that are easier to analyze. Systems of the NMA–water–osmolyte-type were used to test the method and to elucidate information on the interactions between N-Methylacetamide (NMA, a simple peptide model) with stabilizing (trimethylamine N-oxide, glycine, glycine betaine) and destabilizing osmolytes (n-butylurea and tetramethylurea). Systems that contain stabilizers change their vibrational structure to a lesser extent than those with denaturants. Changes in the latter are strong and can be related to the formation of direct NMA–destabilizer interactions.

Acute and Chronic Hyponatremia

Hyponatremia is the most common electrolyte disorder in clinical practice. Catastrophic complications can occur from severe acute hyponatremia and from inappropriate management of acute and chronic hyponatremia. It is essential to define the hypotonic state associated with hyponatremia in order to plan therapy. Understanding cerebral defense mechanisms to hyponatremia are key factors to its manifestations and classification and subsequently to its management. Hypotonic hyponatremia is differentiated on the basis of urine osmolality, urine electrolytes and volume status and its treatment is decided based on chronicity and the presence or absence of central nervous (CNS) symptoms. Proper knowledge of sodium and water homeostasis is essential in individualizing therapeutic plans and avoid iatrogenic complications while managing this disorder.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

Understanding the roles of osmolytes for acclimatizing plants to changing environment: a review of potential mechanism

Abiotic stresses are significant environmental issues that restrict plant growth, productivity, and survival while also posing a threat to global food production and security. Plants produce compatible solutes known as osmolytes to adapt themselves in such changing environment. Osmolytes contribute to homeostasis maintenance, provide the driving gradient for water uptake, maintain cell turgor by osmotic adjustment, and redox metabolism to remove excess level of reactive oxygen species (ROS) and reestablish the cellular redox balance as well as protect cellular machinery from osmotic stress and oxidative damage. Perceiving the mechanisms how plants interpret environmental signals and transmit them to cellular machinery to activate adaptive responses is important for crop improvement programs to get stress-tolerant varieties. A large number of studies conducted in the last few decades have shown that osmolytes accumulate in plants and have strong associations with abiotic stress tolerance. Production of abundant osmolytes is needed for tolerance in many plant species. In addition, transgenic plants overexpressing genes for different osmolytes showed enhanced tolerance to various abiotic stresses. Many important aspects of their mechanisms of action are yet to be largely identified, especially regarding the relevance and relative contribution of specific osmolytes to the stress tolerance of a given species. Therefore, more efforts and resources should be invested in the study of the abiotic stress responses of plants in their natural habitats. The present review focuses on the possible roles and mechanisms of osmolytes and their association toward abiotic stress tolerance in plants. This review would help the readers in learning more about osmolytes and how they behave in changing environments as well as getting an idea of how this knowledge could be applied to develop stress tolerance in plants.

Liquid-liquid phase separation of the intrinsically disordered AB region of hRXRγ is driven by hydrophobic interactions

Nuclear receptors (NRs) are a family of transcription factors that are regulated endogenously by small lipophilic ligands. Recently, liquid-liquid phase separation (LLPS) has appeared as a new aspect of NR function. In the human retinoid X receptor γ (hRXRγ), the inherently disordered AB region undergoes LLPS via homotypic multivalent interactions. To better understand the functions of liquid condensates, a clear view of the molecular interactions underlying the LLPS are required. The phase separation propensity of the AB region of hRXRγ (AB_hRXG) at a high NaCl concentration, a lower critical solution temperature behavior, and also sensitivity to kosmotropic salts and 1,6-hexanediol, which all indicate the importance of hydrophobic interactions in the formation of AB_hRXG liquid condensates, is presented in the paper. Additionally, molecular crowding agents and TMAO shift the equilibrium, in turn enabling phase transition at lower AB_hRXG concentrations. Although the LLPS of the proteins can lead to aggregation, AB_hRXG liquid condensates are not aggregation prone. Interestingly, the formation of AB_hRXG liquid condensates has an impact on the rest of the receptor, as AB_hRXG liquid condensates recruit the remaining fragment of hRXRγ into the droplets. The ability of AB_hRXG to undergo LLPS might be important for gene expression regulation.

Osmoprotectant Coated Thermostable Gold Nanoparticles Efficiently Restrict Temperature-Induced Amyloid Aggregation of Insulin

Naturally occurring osmoprotectants are known to prevent aggregation of proteins under various stress factors including extreme pH and elevated temperature conditions. Here, we synthesized gold nanoparticles coated with selected osmolytes (proline, hydroxyproline, and glycine) and examined their effect on temperature-induced amyloid-formation of insulin hormone. These uniform, thermostable, and hemocompatible gold nanoparticles were capable of inhibiting both spontaneous and seed-induced amyloid aggregation of insulin. Both quenching and docking experiments suggest a direct interaction between the osmoprotectant-coated nanoparticles and aggregation-prone hydrophobic stretches of insulin. Circular-dichroism results confirmed the retention of insulin's native structure in the presence of these nanoparticles. Unlike the indirect solvent-mediated effect of free osmolytes, the inhibition effect of osmolyte-coated gold nanoparticles was observed to be mediated through their direct interaction with insulin. The results signify the protection of the exposed aggregation-prone domains of insulin from temperature-induced self-assembly through osmoprotectant-coated nanoparticles, and such effect may inspire the development of osmolyte-based antiamyloid nanoformulations.

Chirality-Dependent Amino Acid Modulation of RNA Folding

The preponderance of a specific d- or l-chirality in fats, sugars, amino acids, nucleic acids, and so on is ubiquitous in nature, yet the biological origin of such chiral dominance (i.e., with one enantiomer overwhelmingly present) remains an open question. One plausible proposal for the predominance of l-chirality in amino acids could be through evolutionary templating of chiral RNA-folding via chaperone activity. To help evaluate this possibility, single molecule fluorescence experiments have been performed that measure the chiral dependence of chaperone folding dynamics for the simple tetraloop-tetraloop receptor (TL-TLR) tertiary binding motif in the presence of a series of chiral amino acids. Specifically, d- vs l-arginine is found to accelerate the unfolding of this RNA motif in a chirally selective fashion, with temperature-dependent studies of the kinetics performed to extract free energy, enthalpy, and entropy landscapes for the underlying thermodynamics. Furthermore, all-atom molecular dynamics (MD) simulations are pursued to provide additional physical insight into this chiral sensitivity, which reveal enantiomer-specific sampling of nucleic acid surfaces by d- vs l-arginine and support a putative mechanism for chirally specific denaturation of RNA tertiary structure by arginine but not other amino acids.

An improved strategy of TGFβ3 expression in Escherichia coli: Exploiting folding modulators for a switch from misfolded to folded form

Transforming growth factor beta 3 (TGFβ3) exhibits a complex native structure featuring the presence of multiple disulfide bonds forming the active dimer. Consequently, its heterologous expression in microbial system invariably leads to inclusion body (IB) formation. In this study, we observed an interesting phenomenon of switching a significant fraction of misfolded TGFβ3 to folded form by modulating the cellular protein folding machinery. We carried out co-expression experiments with chaperones and demonstrated the requirement of a coordinated action of DnaK-DnaJ-GrpE and GroESL, to achieve the native soluble conformation of TGFβ3, during over-expression in E. coli. The novelty of this study lies in the fact that orchestration of a group of chaperones to work in concert for efficient folding and assembly of TGFβ3-like cytokines has not been widely explored. Additionally, we have also demonstrated that presence of osmolytes (sorbitol or trehalose) in the growth media have an appreciable impact on the solubility of TGFβ3. We have further shown a synergism between the effects of molecular chaperone and osmolytes on the solubility of TGFβ3. We have confirmed the functionality of soluble TGFβ3 by performing binding interactions with its cognate receptor TβRII. Our study delineates the fact that an effective combination of chaperones or optimum concentration of compatible osmolyte, can efficiently abrogate competing aggregation pathways and help attain the native conformation of a cysteine rich cytokine in a facile manner.

New insight into the molecular mechanism of the trehalose effect on urate oxidase stability

Urate oxidase (EC 1.7.3.3) is a key enzyme in the purine metabolism which is applied in the treatment of gout and also, as a diagnostic reagent for uric acid detection. In the current study, the trehalose (TRE) effects as an additive on the structural stability and function of uricase were investigated. For recombinant expression of UOX in E. coli BL21 cells, firstly the coding sequence was subcloned into the pET-28a vector and after induction with IPTG, the recombinant UOX was purified by affinity chromatography using a Ni-NTA agarose column. To specify the trehalose effects on the urate oxidase (UOX) structure, optimum pH, optimum temperature, kinetic and thermodynamic parameters and also, the intrinsic fluorescence of UOX in the absence and presence of trehalose were examined. The UOX half-life is 24.32 min at 40 °C, whereas the UOX-TRE has a higher half-life (32.09 min) at this temperature. Generally, our findings confirm that trehalose has a protective effect on the enzyme structure. Optimum pH and temperature were 9 and 25 °C, respectively for both the naked and treated enzymes and their activity retained 42.18 and 64.80%, respectively after 48 h of incubation at room temperature. Also, theoretical results indicate that the random coil of the enzyme was converted to α-helix and β-sheet in the presence of trehalose which may preserve the integrity of the active site of the enzyme and increased the enzymatic activity. The MD simulation results indicated greater stability of the uricase structure in the presence of trehalose.Communicated by Ramaswamy H. Sarma.

Investigating the effect of sugar-terminated nanoparticles on amyloid fibrillogenesis of β-lactoglobulin

In vivo tissue deposition of fibrillar protein aggregates is the cause of several degenerative diseases. Evidence suggests that interfering with the pathology-associated amyloid fibrillogenesis by inhibitory molecules is envisaged as the primary therapeutic strategy. Amyloid fibril formation of proteins has been demonstrated to be influenced by nanoparticles/nanomaterials. As compared with their molecular form counterpart, this work examined the effect of sucrose-terminated nanoparticles on the in vitro amyloid fibrillogenesis and structural properties of β-lactoglobulin at pH 2.0 and 80 °C. ThT binding and electron microscopy results demonstrated that sucrose-terminated nanoparticles were able to suppress β-lactoglobulin fibrillogenesis in a concentration-dependent fashion. Importantly, sucrose-terminated nanoparticles showed better β-lactoglobulin fibril-inhibiting ability than sucrose molecules. ANS fluorescence and right-angle light scattering results showed reduced solvent exposure and decreased aggregation, respectively, in the β-lactoglobulin samples upon treatment with sucrose-terminated nanoparticles. Moreover, fluorescence quenching analyses revealed that the static quenching mechanism and formation of a non-fluorescent fluorophore-nanoparticle complex are involved in the nanoparticle-β-lactoglobulin interaction. We believe that the results from this study may suggest that the nanoparticle form of biocompatible sugar-related osmolytes may serve as effective inhibiting/suppressing agents toward protein fibrillogenesis.

Trehalose Conjugates of Silybin as Prodrugs for Targeting Toxic Aβ Aggregates

Alzheimer's disease (AD) is linked to the abnormal accumulation of amyloid β peptide (Aβ) aggregates in the brain. Silybin B, a natural compound extracted from milk thistle (Silybum marianum), has been shown to significantly inhibit Aβ aggregation in vitro and to exert neuroprotective properties in vivo. However, further explorations of silybin B's clinical potential are currently limited by three main factors: (a) poor solubility, (b) instability in blood serum, and (c) only partial knowledge of silybin's mechanism of action. Here, we address these three limitations. We demonstrate that conjugation of a trehalose moiety to silybin significantly increases both water solubility and stability in blood serum without significantly compromising its antiaggregation properties. Furthermore, using a combination of biophysical techniques with different spatial resolution, that is, TEM, ThT fluorescence, CD, and NMR spectroscopy, we profile the interactions of the trehalose conjugate with both Aβ monomers and oligomers and evidence that silybin may shield the "toxic" surfaces formed by the N-terminal and central hydrophobic regions of Aβ. Finally, comparative analysis with silybin A, a less active diastereoisomer of silybin B, revealed how even subtle differences in chemical structure may entail different effects on amyloid inhibition. The resulting insight on the mechanism of action of silybins as aggregation inhibitors is anticipated to facilitate the future investigation of silybin's therapeutic potential.

NFAT5, which protects against hypertonicity, is activated by that stress via structuring of its intrinsically disordered domain

Nuclear Factor of Activated T cells 5 (NFAT5) is a transcription factor (TF) that mediates protection from adverse effects of hypertonicity by increasing transcription of genes, including those that lead to cellular accumulation of protective organic osmolytes. NFAT5 has three intrinsically ordered (ID) activation domains (ADs). Using the NFAT5 N-terminal domain (NTD), which contains AD1, as a model, we demonstrate by biophysical methods that the NTD senses osmolytes and hypertonicity, resulting in stabilization of its ID regions. In the presence of sufficient NaCl or osmolytes, trehalose and sorbitol, the NFAT5 NTD undergoes a disorder-to-order shift, adopting higher average secondary and tertiary structure. Thus, NFAT5 is activated by the stress that it protects against. In its salt and/or osmolyte-induced more ordered conformation, the NTD interacts with several proteins, including HMGI-C, which is known to protect against apoptosis. These findings raise the possibility that the increased intracellular ionic strength and elevated osmolytes caused by hypertonicity activate and stabilize NFAT5.

Organic osmolytes increase expression of specific tight junction proteins in skin and alter barrier function in keratinocytes

BACKGROUND

The epidermal barrier is important for water conservation, failure of which is evident in dry-skin conditions. Barrier function is fulfilled by the stratum corneum, tight junctions (TJs, which control extracellular water) and keratinocyte mechanisms, such as organic osmolyte transport, which regulate intracellular water homeostasis. Organic osmolyte transport by keratinocytes is largely unexplored and nothing is known regarding how cellular and extracellular mechanisms of water conservation may interact.

OBJECTIVES

We aimed to characterize osmolyte transporters in skin and keratinocytes, and, using transporter inhibitors, to investigate whether osmolytes can modify TJs. Such modification would suggest a possible link between intracellular and extracellular mechanisms of water regulation in skin.

METHODS

Immunostaining and quantitative polymerase chain reaction of organic osmolyte-treated organ-cultured skin were used to identify changes to organic osmolyte transporters, and TJ protein and gene expression. TJ functional assays were performed on organic osmolyte-treated primary human keratinocytes in culture.

RESULTS

Immunostaining demonstrated the expression of transporters for betaine, taurine and myo-inositol in transporter-specific patterns. Treatment of human skin with either betaine or taurine increased the expression of claudin-1, claudin-4 and occludin. Osmolyte transporter inhibition abolished this response. Betaine and taurine increased TJ function in primary human keratinocytes in vitro.

CONCLUSIONS

Treatment of skin with organic osmolytes modulates TJ structure and function, which could contribute to the epidermal barrier. This emphasizes a role for organic osmolytes beyond the maintenance of intracellular osmolarity. This could be harnessed to enhance topical therapies for diseases characterized by skin barrier dysfunction.

Mitigating effects of osmolytes on the interactions between nanoparticles and supported lipid bilayer

To maintain osmotic balance, cells usually produce neutral solutes (i.e., osmolytes), together with charged species to cope with salinity stress. Osmolytes are known to be important in stabilizing/destabilizing macromolecules (e.g., proteins) via depletion /accumulation around their surfaces. To better understand the physiological fate of nanoparticles (NPs), we investigated the effect of osmolytes [(urea and trimethylamine N-oxide (TMAO)] and specific anions (NO₃^- and F^-) on the interactions between NPs and supported lipid bilayers (SLBs). Carboxylated polystyrene NPs (60 nm) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were chosen as model NPs and lipid. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to quantify NP deposition dynamics. Microscale thermophoresis (MST) was used to characterize the affinity between DOPC vesicles (or NPs) and osmolytes. Our results show that osmolytes are capable of protecting SLBs from NP-induced disruption. Upon NP deposition onto supported vesicle layers (SVLs), the leakage of encapsulated dyes decreased with the addition of osmolytes. The combination of kosmotropes (TMAO and F^-) are more efficient than that of chaotropes (urea and NO₃^-) in weakening the hydrophobic interaction between NPs and SLBs by preferential binding to NPs and/or SLBs.

Surface hydration and preferential interaction directs the charged amino acids-induced changes in protein stability

In the present study, we investigate the interaction of amino acid osmolytes, Arg, Lys, Asp and Glu, and a denaturant, guanidinium chloride (Gdm) with proteins. To achieve this, molecular dynamics (MD) simulation of RNase A and α-lactalbumin was performed in the presence of three charged amino acids Arg, Lys, and Asp and the molecular mechanism of amino acid-induced (de)stabilization of the proteins was examined by combining with our earlier report on Glu. As Arg has the side chain similar to that of Gdm and destabilizes the proteins, MD simulation was carried out in the presence of Gdm as well. Radial distribution function and hydration fraction around the protein surface reveals that preferential hydration increases upon the addition of any of the cosolvent; however, the extent of increase is more in the presence of stabilizing cosolvents (stAAs: Lys, Asp and Glu) compared to destabilizing cosolvents (Arg and Gdm). Moreover, the preferential interaction of Arg and Gdm with the proteins is higher than that of stAAs. Residue-level interaction analysis suggests that stAAs preferably interacts with charged amino acids of the proteins whereas Arg and Gdm interactions could be found on almost all the surface exposed residues which might provide higher preferential interaction for these residues. From the results, we propose that the net outcome of preferential hydration versus preferential interaction of the amino acids might determine their effect on the stability of proteins.

Betaine addition as a potent ruminal fermentation modulator under hyperthermal and hyperosmotic conditions in vitro

BACKGROUND

Climatic and dietary shifts predispose ruminal microbes to hyperthermal and hyperosmotic stress, leading to poor fermentation and subsequently adverse effects on ruminant productivity. Betaine may function as substrate, osmolyte, antioxidant, and methyl donor for microbes. However, its effect depends on the extent of microbial catabolism. This study revealed the ruminal disappearance kinetics of betaine and its dose effect on ruminal fermentation during thermal and osmotic stress using a rumen simulation technique.

RESULTS

Three different betaine doses were used: 0, 50, and 286 mg L^-1 ; each was assigned to two incubation temperatures (39.5 and 42 °C) and two osmotic conditions (295 and 420 mOsmol kg^-1 ). Betaine disappeared rapidly within the first 6 h of incubation; however, the rate was lower during hyperosmotic stress (P < 0.05), the stress condition that also suppressed the overall fermentation and degradation of organic nutrients and decreased the bacterial diversity (P < 0.001). During hyperosmotic stress, betaine shifted the fermentation pathway to more propionate (P < 0.05). Betaine counteracted the negative effect of hyperthermal stress on total short-chain fatty acid concentration (P < 0.05) without affecting the composition. Both stress conditions shifted the bacterial composition, but the effect of betaine was minimal.

CONCLUSION

Despite its rapid ruminal disappearance, betaine modulated microbial fermentation in different ways depending on stress conditions, indicating the plasticity of the betaine effect in response to various kinds of physicochemical stress. Although betaine did not affect the abundance of ruminal microbiota, the enhanced fermentation suggests an improved microbial metabolic activity under stress conditions. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Taurine Induces an Ordered but Functionally Inactive Conformation in Intrinsically Disordered Casein Proteins

Intrinsically disordered proteins (IDPs) are involved in various important biological processes, such as cell signalling, transcription, translation, cell division regulation etc. Many IDPs need to maintain their disordered conformation for proper function. Osmolytes, natural organic compounds responsible for maintaining osmoregulation, have been believed to regulate the functional activity of macromolecules including globular proteins and IDPs due to their ability of modulating the macromolecular structure, conformational stability, and functional integrity. In the present study, we have investigated the effect of all classes of osmolytes on two model IDPs, α- and β-casein. It was observed that osmolytes can serve either as folding inducers or folding evaders. Folding evaders, in general, do not induce IDP folding and therefore had no significant effect on structural and functional integrity of IDPs. On the other hand, osmolytes taurine and TMAO serve as folding inducers by promoting structural collapse of IDPs that eventually leads to altered structural and functional integrity of IDPs. This study sheds light on the osmolyte-induced regulation of IDPs and their possible role in various disease pathologies.

Osmolytes: A Possible Therapeutic Molecule for Ameliorating the Neurodegeneration Caused by Protein Misfolding and Aggregation

Most of the neurological disorders in the brain are caused by the abnormal buildup of misfolded or aggregated proteins. Osmolytes are low molecular weight organic molecules usually built up in tissues at a quite high amount during stress or any pathological condition. These molecules help in providing stability to the aggregated proteins and protect these proteins from misfolding. Alzheimer’s disease (AD) is the uttermost universal neurological disorder that can be described by the deposition of neurofibrillary tangles, aggregated/misfolded protein produced by the amyloid β-protein (Aβ). Osmolytes provide stability to the folded, functional form of a protein and alter the folding balance away from aggregation and/or degradation of the protein. Moreover, they are identified as chemical chaperones. Brain osmolytes enhance the pace of Aβ aggregation, combine with the nearby water molecules more promptly, and avert the aggregation/misfolding of proteins by providing stability to them. Therefore, osmolytes can be employed as therapeutic targets and may assist in potential drug design for many neurodegenerative and other diseases.

Osmolyte transporter expression is reduced in photoaged human skin: Implications for skin hydration in aging

Aging is characterized by the deterioration of tissue structure and function. In skin, environmental factors, for example, ultraviolet radiation (UVR), can accelerate the effects of aging such as decline in barrier function and subsequent loss of hydration. Water homeostasis is vital for all cellular functions and it is known that organic osmolyte transport is critical to this process. Therefore, we hypothesized that as we age, these tightly controlled physiological mechanisms become disrupted, possibly due to loss of transporter expression. We investigated this in vivo, using human skin samples from photoprotected and photoexposed sites of young and aged volunteers. We show a reduction in keratinocyte cell size with age and a downregulation of osmolyte transporters SMIT and TAUT with both chronic and acute UVR exposure. Single‐cell live imaging demonstrated that aged keratinocytes lack efficient cell volume recovery mechanisms possessed by young keratinocytes following physiological stress. However, addition of exogenous taurine significantly rescued cell volume; this was corroborated by a reduction in TAUT mRNA and protein in aged, as compared to young, keratinocytes. Collectively, these novel data demonstrate that human epidermal keratinocytes possess osmolyte‐mediated cell volume regulatory mechanisms, which may be compromised in aging. Therefore, this suggests that organic osmolytes—especially taurine—play a critical role in cutaneous age‐related xerosis and highlights a fundamental mechanism, vital to our understanding of the pathophysiology of skin aging.

A computational approach to get insights into multiple faces of additives in modulation of protein aggregation pathways

An enormous population worldwide is presently confronted with debilitating neurodegenerative diseases. The etiology of the disease is connected to protein aggregation and the events involved therein. Thus, a complete understanding of an inhibitor at different stages in the process is imperative for the formulation of a drug molecule. This review presents a detailed summary of the current status of different cosolvents. It further develops how the complex aggregation pathway can be simplified into three steps common to all proteins and the way computer simulations can be exploited to gain insights into the ways by which known inhibitors can affect all these stages. Computation of theoretical parameters in this regard and their correlation with experimental techniques is accentuated. In addition to providing an outline of the scope of different additives, this review showcases the way by which the problem of analyzing an effect of an additive can be addressed effectively via MD simulations.

Osmolytes ameliorate the effects of stress in the absence of the heat shock protein Hsp104 in Saccharomyces cerevisiae

Aggregation of the prion protein has strong implications in the human prion disease. Sup35p is a yeast prion, and has been used as a model protein to study the disease mechanism. We have studied the pattern of Sup35p aggregation inside live yeast cells under stress, by using confocal microscopy, fluorescence activated cell sorting and western blotting. Heat shock proteins are a family of proteins that are produced by yeast cells in response to exposure to stressful conditions. Many of the proteins behave as chaperones to combat stress-induced protein misfolding and aggregation. In spite of this, yeast also produce small molecules called osmolytes during stress. In our work, we tried to find the reason as to why yeast produce osmolytes and showed that the osmolytes are paramount to ameliorate the long-term effects of lethal stress in Saccharomyces cerevisiae, either in the presence or absence of Hsp104p.

Stabilizing osmolytes' effects on the structure, stability and function of tc-tenecteplase: A one peptide bond digested form of tenecteplase

Organic osmolytes, as major cellular compounds, cause protein stabilization in the native form. In the present study, the possible chaperone effects of the three naturally occurring osmolytes on the two-chain form of tenecteplase (tc-TNK), a recombinant, genetically engineered mutant tissue plasminogen activator, have been explored by using circular dichroism, steady-state fluorescence, UV-Visible spectroscopy, and in silico experiments. The tc-TNK is derived from the one-chain protein upon disruption of one peptide bond. Thermal denaturation experiments showed a slightly more stabilizing effect of the three co-solvents on the single-chain TNK (sc-TNK) in comparison to that on tc-TNK. Unlike single-chain tenecteplase, the two-chain form undergoes reversible denaturation which is somehow perturbed in some cases as the result of the presence of osmolytes. Very minor changes in the secondary structure and the tertiary structure were observed. The molecular dynamics simulations and comparative structural analysis of catalytic domain of the protein in the single-chain and two-chain forms in pure water, mannitol/water, trehalose/water, and sucrose/water showed that while the stabilizing effect of the three osmolytes on tc-TNK might be induced by preferential accumulation of these molecules around the nonpolar and aromatic residues, that is to say, fewer water-hydrophobic residues' interactions in tc-TNK, sc-TNK is stabilized by preferential exclusion effect.

Pollen Developmental Arrest: Maintaining Pollen Fertility in a World With a Changing Climate

During evolution of land plants, the haploid gametophytic stage has been strongly reduced in size and the diploid sporophytic phase has become the dominant growth form. Both male and female gametophytes are parasitic to the sporophyte and reside in separate parts of the flower located either on the same plant or on different plants. For fertilization to occur, bi-cellular or tri-cellular male gametophytes (pollen grains) have to travel to the immobile female gametophyte in the ovary. To survive exposure to a hostile atmosphere, pollen grains are thought to enter a state of complete or partial developmental arrest (DA). DA in pollen is strongly associated with acquisition of desiccation tolerance (DT) to extend pollen viability during air travel, but occurrence of DA in pollen is both species-dependent and at the same time strongly dependent on the reigning environmental conditions at the time of dispersal. Several environmental stresses (heat, drought, cold, humidity) are known to affect pollen production and viability. Climate change is also posing a serious threat to plant reproductive behavior and crop productivity. It is therefore timely to gain a better understanding of how DA and pollen viability are controlled in plants and how pollen viability can be protected to secure crop yields in a changing environment. Here, we provide an overview of how DA and pollen viability are controlled and how the environment affects them. We make emphasis on what is known and areas where a deeper understanding is needed.

Spatial distribution mapping of molecules in the grains of different rice landraces, using desorption electrospray ionization mass spectrometry

RATIONALE

Documentation of the metabolite profiles of rice landraces is essential as most of them have been lost due to the conventional practices of cultivation. Therefore, application of mass spectrometry imaging (MSI) will be an appropriate analytical platform for molecular profiling, as it can provide a detailed understanding of the site-specific localization patterns of biomolecules, and the cues concerning metabolic pathways in organisms.

METHODS

Desorption electrospray ionization mass spectrometry (DESI-MS) is a relatively non-destructive analytical technique for surface sampling in natural conditions. Here, we report the spatial distribution of diverse molecules in the grains of different rice landraces of India using DESI-MSI. Molecules were identified by ESI-MS and tandem MS analysis of rice extracts. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used for the elemental mapping on the rice grains.

RESULTS

DESI-MSI showed a uniform distribution of choline (m/z 104.1), sucrose in the form of its sodium (m/z 365.1) and potassium (m/z 381.0) adducts, linoleic acid (m/z 279.2), 13-HODE-9-HODE (m/z 295.2), unidentified molecules with m/z 535.3, 559.5, and 561.5 and isoschaftoside (m/z 563.1) in the endosperm of rice grains. Gluconic acid (m/z 195.0) and signalling phospholipid intermediate molecules were localized in the embryo whereas oryzanol A (m/z 601.5) and oryzanol C (m/z 615.5) had a restricted localization in the bran region of the grain. SEM-EDS mapping showed the localization of potassium and phosphorus along the bran and embryo.

CONCLUSIONS

DESI-MSI revealed the distribution of lipids and sugar molecules in the specific regions of the rice grains. Thus, molecules unique to some rice varieties were identified with this analytical platform. Mass spectrometry imaging of rice along with the elemental mapping by SEM-EDS will be of use in understanding the localization pattern of certain molecules in the context of metals present in the grain.

Spatial and Temporal Profile of Glycine Betaine Accumulation in Plants Under Abiotic Stresses

Several halophytes and a few crop plants, including Poaceae, synthesize and accumulate glycine betaine (GB) in response to environmental constraints. GB plays an important role in osmoregulation, in fact, it is one of the main nitrogen-containing compatible osmolytes found in Poaceae. It can interplay with molecules and structures, preserving the activity of macromolecules, maintaining the integrity of membranes against stresses and scavenging ROS. Exogenous GB applications have been proven to induce the expression of genes involved in oxidative stress responses, with a restriction of ROS accumulation and lipid peroxidation in cultured tobacco cells under drought and salinity, and even stabilizing photosynthetic structures under stress. In the plant kingdom, GB is synthesized from choline by a two-step oxidation reaction. The first oxidation is catalyzed by choline monooxygenase (CMO) and the second oxidation is catalyzed by NAD+-dependent betaine aldehyde dehydrogenase. Moreover, in plants, the cytosolic enzyme, named N-methyltransferase, catalyzes the conversion of phosphoethanolamine to phosphocholine. However, changes in CMO expression genes under abiotic stresses have been observed. GB accumulation is ontogenetically controlled since it happens in young tissues during prolonged stress, while its degradation is generally not significant in plants. This ability of plants to accumulate high levels of GB in young tissues under abiotic stress, is independent of nitrogen (N) availability and supports the view that plant N allocation is dictated primarily to supply and protect the growing tissues, even under N limitation. Indeed, the contribution of GB to osmotic adjustment and ionic and oxidative stress defense in young tissues, is much higher than that in older ones. In this review, the biosynthesis and accumulation of GB in plants, under several abiotic stresses, were analyzed focusing on all possible roles this metabolite can play, particularly in young tissues.