Second virial coefficients as a measure of protein--osmolyte interactions

The cytoplasm contains high concentrations of cosolutes. These cosolutes include macromolecules and small organic molecules called osmolytes. However, most biophysical studies of proteins are conducted in dilute solutions. Two broad classes of models have been used to describe the interaction between osmolytes and proteins. One class focuses on excluded volume effects, while the other focuses on binding between the protein and the osmolyte. To better understand protein--smolyte interactions, we have conducted sedimentation equilibrium analytical ultracentrifugation experiments using ferricytochrome c as a model protein. From these experiments, we determined the second virial coefficients for a series of osmolytes. We have interpreted the second virial coefficient as a measure of both excluded volume and protein--osmolyte binding. We conclude that simple models are not sufficient to understand the interactions between osmolytes and proteins.     

The novel strain Desmonostoc salinum CCM-UFV059 shows higher salt and desiccation resistance compared to the model strain Nostoc sp. PCC7120

Desmonostoc salinum CCM-UFV059 (Desmonostoc) is a novel cyanobacterial strain of the order Nostocales isolated from a saline-alkaline lake. The acclimation towards salt and desiccation stress of Desmonostoc was compared to the related and well-characterized model strain Nostoc sp. PCC7120 (Nostoc). Salt–stressed cells of Desmonostoc maintained low cellular Na⁺ concentrations and accumulated high amounts of compatible solutes, mainly sucrose and to a lower extent trehalose. These features permitted Desmonostoc to grow and maintain photosynthesis at 2-fold higher salinities than Nostoc. Moreover, Desmonostoc also induced sucrose over-accumulation under desiccation, which allowed this strain to recover from this stress in contrast to Nostoc. Additional mechanisms such as the presence of highly unsaturated lipids in the membrane and an efficient ion transport system could also explain, at least partially, how Desmonostoc is able to acclimate to high salinities and to resist longer desiccation periods. Collectively, our results provide first insights into the physiological and metabolic adaptations explaining the remarkable high salt and desiccation tolerance, which qualify Desmonostoc as an attractive model for further analysis of stress acclimation among heterocystous N₂–fixing cyanobacteria.     

Insights into the disparate action of osmolytes and macromolecular crowders on amyloid formation

It is widely recognized that amyloid formation sensitively responds to conditions set by myriad cellular solutes. These cosolutes include two important classes: macromolecular crowders and compatible osmolytes. We have recently found that addition of macromolecular PEG only slightly affects fibril formation of a model peptide in vitro. Polyol osmolytes, in contrast, lengthen the lag time for aggregation, and lead to larger fibril mass at equilibrium. To further hypothesize on the molecular underpinnings of the disparate effect of the two cosolute classes, we have further analyzed the experiments using an available kinetic mechanism describing fibril aggregation. Model calculations suggest that all cosolutes similarly lengthen the time required for nucleation, possibly due to their excluded volume effect. However, PEGs may in addition promote fibril fragmentation, leading to lag times that are overall almost unvaried. Moreover, polyols effectively slow the monomer-fibril detachment rates, thereby favoring additional fibril formation. Our analysis provides first hints that cosolutes act not only by changing association or dissociation rates, but potentially also by directing the formation of fibrils of varied morphologies with different mechanical properties. Although additional experiments are needed to unambiguously resolve the action of excluded cosolutes on amyloid formation, it is becoming clear that these compounds are important to consider in the search for ways to modulate fibril formation.     

Water‐compatible silica sol–gel molecularly imprinted polymer as a potential delivery system for the controlled release of salicylic acid

Molecularly imprinted polymers (MIPs) for salicylic acid were synthesized and evaluated in aqueous environments in the aim to apply them as drug delivery carriers. One organic MIP and one inorganic MIP based on the sol–gel process were synthesized. The organic MIP was prepared by radical polymerization using the stoichiometric functional monomer, 1‐(4‐vinylphenyl)‐3‐(3,5‐bis(trifluoromethyl)phenyl)urea, which can establish strong electrostatic interactions with the –COOH of salicylic acid. The sol–gel MIP was prepared with 3‐(aminopropyl)triethoxysilane and trimethoxyphenylsilane, as functional monomers and tetraethyl orthosilicate as the crosslinker. While the organic MIPs bound the target specifically in acetonitrile, they exhibited lower binding in the presence of water, although the imprinting factor increased under these conditions, due to reduced non‐specific binding. The sol–gel MIP has a high specificity and capacity for the drug in ethanol, a solvent compatible with drug formulation and biomedical applications. In vitro release profiles of the polymers in water were evaluated, and the results were modelled by Fick's law of diffusion and the power law. Analysis shows that the release mechanism was predominantly diffusion‐controlled. Copyright © 2014 John Wiley & Sons, Ltd.     

Self-assembled monolayer coating of biological probes to avoid protein adhesion

Probes designed to locally illuminate structures within plant cells are described. The probes studied are etch-sharpened single mode optical fibers, coated with aluminum, similar to probes used for near-field scanning optical microscopy. We find that cellular material adheres to the probes that are not coated with a self-assembled monolayer octadecyltrichlorosilane. The hydrophobic monolayer coating enabled these probes to be inserted into and removed from plant cells with no protein adhesion to the probes. This allows probe reinsertion and it causes less damage to the target cell, greatly facilitating in vivo optical study of cells.     

Stress response and tolerance of the submerged macrophyte Elodea nuttallii (Planch) St. John to heat stress: a comparative study of shock heat stress and gradual heat stress

Sudden and gradual increases of temperature in aquatic environments play important roles in determining growth and physiological dynamics of aquatic macrophytes. However, a lesser attention has been paid to identify the effects of different temperature regimes on aquatic macrophytes. Therefore, the present study is focused on comparing the effects of shock and gradual heat stresses (SHS and GHS) on growth, photosynthetic attributes, and oxidative damage on Elodea nuttallii as a model plant. Laboratory-oriented two experimental setups were maintained to induce the SHS and GHS. A significant decline in shoot elongation coupled with a decline in endogenous indoleacetic acid (IAA) and an increase in hydrogen peroxide (H₂O₂) was observed in both temperature treatments. These effects were further accompanied by oxidative damage to photosynthetic pigments and cell membrane structures in E. nuttallii. Temperature-mediated oxidative stress was significantly pronounced under SHS, which induced the activation of different defensive mechanisms against reactive oxygen species, including antioxidant enzymes, secondary metabolites, and osmoprotectants. The present study revealed that temperature-induced oxidative damage was more severe when the temperature increased suddenly. Further, heat acclimation was observed when the plant was exposed to 30 °C under GHS, although this treatment induces significant oxidative stress under 35 °C.     

Compatible solute addition to biological systems treating waste/wastewater to counteract osmotic and other environmental stresses: a review

This study reviews the addition of compatible solutes to biological systems as a strategy to counteract osmolarity and other environmental stresses. At high osmolarity many microorganisms accumulate organic solutes called “compatible solutes” in order to balance osmotic pressure between the cytoplasm and the environment. These organic compounds are called compatible solutes because they can function inside the cell without the need for special adaptation of the intracellular enzymes, and also serve as protein stabilizers in the presence of high ionic strength. Moreover, the compatible solutes strategy is regularly being employed by the cell, not only under osmotic stress at high salinity, but also under other extreme environmental conditions such as low temperature, freezing, heat, starvation, dryness, recalcitrant compounds and solvent stresses. The accumulation of these solutes from the environment has energetically a lower cost than de novo synthesis. Based on this cell mechanism several studies in the field of environmental biotechnology (most of them on biological wastewater treatment) employed this strategy by exogenously adding compatible solutes to the wastewater or medium in order to alleviate environmental stress. This current paper critically reviews and evaluates these studies, and examines the future potential of this approach. In addition to this, a strategy for the successful implementation of compatible solutes in biological systems is proposed.     

Transgenic plants with improved dehydration-stress tolerance: Progress and future prospects

This review summarizes the recent progress made towards the development of transgenic plants with improved tolerance to water stress and salinity. Of the various strategies employed, emphasis has been given to the genes engineered for the biosynthesis of osmoprotectants and osmolytes. This review also briefly discusses the importance of the use of specific stress inducible promoters and the future prospects of transgenic plants with improved agronomic traits.     

Osmoregulation in eukaryotic algae

Abstract The cells of marine and halotolerant eukaryotic algae can achieve osmotic balance by ion accumulation mechanisms or by the synthesis and degradation of compatible solutes. The latter mechanism has been extensively studied in Dunaliella tertiolecta , in which the compatible solute glycerol is synthesised and metabolised through the glycerol cycle. Osmoregulation in Poterioochromonas malhamensis by isofloridoside as the compatible solute has a different control mechanism. The results obtained with unicellular algae might lead to strategies for the improvement of salt and water stress resistance in crop plants.     

Low-order fine roots of Picea asperata have different physiological mechanisms in response to seasonal freeze and freeze–thaw of soil

• Seasonal soil freezing (F) and freeze–thaw cycles (FTCs) are common natural phenomena in high latitude or altitude areas of the world, and seriously affect plant physiological processes. However, studies on the effect of soil F and FTCs on fine roots are less common, especially in subalpine coniferous forests of western Sichuan, China.
• We set up a controlled experiment in growth chambers to explore the effects of F and FTCs on low-order fine roots of Picea asperata and differential responses of first-order roots and the first three root orders (1st, 2nd and 3rd order roots combined as a unit).
• Soil F and FTCs resulted in serious damage to cell membranes and root vitality of low-order fine roots, accompanied by increased MDA content and O₂·⁻ production. FTCs had a stronger effect than F treatment. In turn, low-order fine roots are the unit that responds to cold stress. These roots had increased unsaturated fatty acid contents, antioxidant enzyme activities, osmolytes and plant hormones contents when acclimation to cold stress. The first-order roots were more sensitive to cold stress than the combined first three root orders for several processes (e.g. antioxidant enzymes, osmolytes and hormones) because of their specific structure and physiological activity.
• This study explains physiological differences in responses of fine roots of different root orders to seasonal soil freezing, which will improve the understanding of fine root heterogeneity and support agriculture and forest management.