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Keywords:
Osmolyte
Methylamines
Chemical chaperone
Extreme ecological surroundings for plants such as drought and water scarcity, varying temperature from minimal to maximum level, and accumulation of salt and heavy metals diminish plant growth and hence need precise alteration or modification. To maintain osmotic harmony, plants secrete osmolytes and osmoprotectants as essential abiotic stress mitigators to encounter harsh environmental conditions through monitoring constant cellular homeostatic. There are some low-molecular-weight, nontoxic compounds that accumulate in plants in response to drought and salinity stress without snooping with normal metabolism. Soluble sugars such as sucrose, hexose, trehalose, RFO, and sugar alcohols and other osmolytes such as glycine betaine and proline amino acid act as the osmoprotectants. These sugars play an important role in the maintenance of cellular organizations, photosynthetic proficiency, and detoxification of reactive oxygen species by acting as metabolic signals in the stress conditions. Together, they shield plants by exercising a number of physiological responses, such as strengthening membrane integrity, harmonizing enzymatic/antioxidant activity, and fulfilling water requirement under several abiotic stresses including pesticide exposure. In spite of the fact that a connection surely exists between the amassing of explicit osmoprotective substances and stress tolerance, a causal connection between osmolyte gathering and improved resistance could not generally be affirmed. This chapter enlightens the mechanisms potentially involved in plant abiotic stress tolerance brought by osmoprotectants as well as concisely highlights important parts so far unmapped in the present framework.
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Betaine
Osmoregulation
Osmotic shock
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Molecular and chemical chaperones are key components of the two main mechanisms that ensure structural stability and activity under environmental stresses. Yet, chemical chaperones are often regarded only as osmolytes and their role beyond osmotic regulation is not fully understood. Here, we systematically studied a large group of chemical chaperones, representatives of diverse chemical families, for their protective influence under either thermal or chemical stresses. Consistent with previous studies, we observed that in spite of the structural similarity between sugars and sugar alcohols, they have an apparent difference in their protective potential. Our results support the notion that the protective activity is mediated by the solvent and the presence of water is essential. In the current work we revealed that i) polyols and sugars have a completely different profile of protective activity toward trifluoroethanol and thermal stress; ii) minor changes in solvent composition that do not affect enzyme activity, yet have a great effect on the ability of osmolytes to act as protectants and iii) increasing the number of active groups of carbohydrates makes them better protectants while increasing the number of active groups of methylamines does not, as revealed by attempts to synthesize de novo designed methylamines with multiple functional groups.
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Methylamines
Chemical chaperone
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Osmolyte
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Cells of almost all organisms accumulate organic osmolytes when exposed to hyperosmolality, most often in the form of high salt or urea. In this review, we discuss 1) how the organic osmolytes protect; 2) the identity of osmolytes in Archaea, bacteria, yeast, plants, marine animals, and mammals; 3) the mechanisms by which they are accumulated; 4) sensors of osmolality; 5) the signaling pathways involved; and 6) mutual counteraction by urea and methylamines.
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Methylamines
Osmoregulation
Intracellular Fluid
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Cells of many organisms accumulate certain small organic molecules -called compatible and counteracting solutes, compensatory solutes, or chemical chaperones – in response to certain physical stresses. These solutes include certain carbohydrates, amino acids, methylamine and methylsulphonium zwitterions, and urea. In osmotic dehydrating stress, these solutes serve as cellular osmolytes. Unlike common salt ions and urea (which inhibit proteins), some organic osmolytes are compatible; i.e., they do not perturb macromolecules such as proteins. In addition, some may protect cells through metabolic processes such as antioxidation reactions and sulphide detoxification. Other osmolytes, and identical or similar solutes accumulated in anhydrobiotic, heat and pressure stresses, are termed counteracting solutes or chemical chaperones because they stabilise proteins and counteract protein-destabilising factors such as urea, temperature, salt, and hydrostatic pressure. Stabilisation of proteins, not necessarily beneficial in the absence of a perturbant, may result indirectly from effects on water structure. Osmotic shrinkage of cells activates genes for chaperone proteins and osmolytes by mechanisms still being elucidated. These solutes have applications in agriculture, medicine and biotechnology.
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Osmotic shock
Chemical chaperone
Osmoregulation
Osmotic pressure
Hydrostatic pressure
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Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. All known osmolytes are amino acids and derivatives, polyols and sugars, methylamines, and urea; unlike salt ions, most are "compatible," i.e., do not perturb macromolecules. In addition, some stabilize macromolecules and are "counteracting" towards perturbants, e.g., methylamines can stabilize proteins and ligand binding against perturbations by urea in elasmobranchs and mammalian kidney, and (our latest findings) high hydrostatic pressure in deep-sea animals. Methylamines appear to coordinate water molecules tightly, resulting in osmolyte exclusion from hydration layers of peptide backbones. This makes unfolded protein conformations entropically unfavorable (work of Timasheff, Galinski, Bolen and coworkers). These properties have led to proposed uses in biotechnology, agriculture and medicine, including improved biochemical methods, in vitro rescue of misfolded proteins in cystic fibrosis and prion diseases (work of Welch and others), and plants engineered for drought and salt tolerance. These properties also explain some but not all of the considerable variation in osmolyte composition among species with different metabolisms and habitats, and among and within mammalian tissues in development.
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Methylamines
Osmoregulation
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Osmolyte
Betaine
Chemical chaperone
Ectoine
Trimethylamine N-oxide
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Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. All known osmolytes are amino acids and derivatives, polyols and sugars, methylamines, and urea; unlike salt ions, most are "compatible," i.e., do not perturb macromolecules. In addition, some stabilize macromolecules and are "counteracting" towards perturbants, e.g., methylamines can stabilize proteins and ligand binding against perturbations by urea in elasmobranchs and mammalian kidney, and (our latest findings) high hydrostatic pressure in deep-sea animals. Methylamines appear to coordinate water molecules tightly, resulting in osmolyte exclusion from hydration layers of peptide backbones. This makes unfolded protein conformations entropically unfavorable (work of Timasheff, Galinski, Bolen and coworkers). These properties have led to proposed uses in biotechnology, agriculture and medicine, including improved biochemical methods, in vitro rescue of misfolded proteins in cystic fibrosis and prion diseases (work of Welch and others), and plants engineered for drought and salt tolerance. These properties also explain some but not all of the considerable variation in osmolyte composition among species with different metabolisms and habitats, and among and within mammalian tissues in development.
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Methylamines
Osmoregulation
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ABSTRACT Osmolyte accumulation and release can protect cells from abiotic stresses. In Escherichia coli , known mechanisms mediate osmotic stress-induced accumulation of K + glutamate, trehalose, or zwitterions like glycine betaine. Previous observations suggested that additional osmolyte accumulation mechanisms (OAMs) exist and their impacts may be abiotic stress specific. Derivatives of the uropathogenic strain CFT073 and the laboratory strain MG1655 lacking known OAMs were created. CFT073 grew without osmoprotectants in minimal medium with up to 0.9 M NaCl. CFT073 and its OAM-deficient derivative grew equally well in high- and low-osmolality urine pools. Urine-grown bacteria did not accumulate large amounts of known or novel osmolytes. Thus, CFT073 showed unusual osmotolerance and did not require osmolyte accumulation to grow in urine. Yeast extract and brain heart infusion stimulated growth of the OAM-deficient MG1655 derivative at high salinity. Neither known nor putative osmoprotectants did so. Glutamate and glutamine accumulated after growth with either organic mixture, and no novel osmolytes were detected. MG1655 derivatives retaining individual OAMs were created. Their abilities to mediate osmoprotection were compared at 15°C, 37°C without or with urea, and 42°C. Stress protection was not OAM specific, and variations in osmoprotectant effectiveness were similar under all conditions. Glycine betaine and dimethylsulfoniopropionate (DMSP) were the most effective. Trimethylamine- N -oxide (TMAO) was a weak osmoprotectant and a particularly effective urea protectant. The effectiveness of glycine betaine, TMAO, and proline as osmoprotectants correlated with their preferential exclusion from protein surfaces, not with their propensity to prevent protein denaturation. Thus, their effectiveness as stress protectants correlated with their ability to rehydrate the cytoplasm.
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Betaine
Dimethylsulfoniopropionate
Osmotic shock
Ectoine
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Organic osmolytes also known as chemical chaperones are major cellular compounds that favor, by an unclear mechanism, protein's compaction and stabilization of the native state. Here, we have examined the chaperone effect of the naturally occurring trimethylamine N-oxide (TMAO) osmolyte on a loosely packed protein (LPP), known to be a highly flexible form, using an apoprotein mutant of the flavin-dependent RNA methyltransferase as a model. Thermal and chemical denaturation experiments showed that TMAO stabilizes the structural integrity of the apoprotein dramatically. The denaturation reaction is irreversible indicating that the stability of the apoprotein is under kinetic control. This result implies that the stabilization is due to a TMAO-induced reconfiguration of the flexible LPP state, which leads to conformational limitations of the apoprotein likely driven by favorable entropic contribution. Evidence for the conformational perturbation of the apoprotein had been obtained through several biophysical approaches notably analytical ultracentrifugation, circular dichroism, fluorescence spectroscopy, labelling experiments and proteolysis coupled to mass spectrometry. Unexpectedly, TMAO promotes an overall elongation or asymmetrical changes of the hydrodynamic shape of the apoprotein without alteration of the secondary structure. The modulation of the hydrodynamic properties of the protein is associated with diverse inhomogenous conformational changes: loss of the solvent accessible cavities resulting in a dried protein matrix; some side-chain residues initially buried become solvent exposed while some others become hidden. Consequently, the TMAO-induced protein state exhibits impaired capability in the flavin binding process. Our study suggests that the nature of protein conformational changes induced by the chemical chaperones may be specific to protein packing and plasticity. This could be an efficient mechanism by which the cell controls and finely tunes the conformation of the marginally stable LPPs to avoid their inappropriate protein/protein interactions and aggregation.
Osmolyte
Chemical chaperone
Chaperone (clinical)
Methylamines
Protein Stability
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