Effect of Oligosaccharides and their Monosaccharide Mixtures on the Stability of Proteins: A Scaled Particle Study

A comparative in silico study to detect the effect of food-additives on metabolic protein and its perturbations compensated by osmolytes

Since its inception, food additive has been an integral part of the food processing industry with various commercial roles. Besides its advantages, various studies have already highlighted its long-term adverse effects on human health. However, in terms of protein structures and functions, the innate mechanism that triggers these effects has not been elucidated in previously reported studies. Our work takes an in silico approach to delve into structural implications resulting from these additives with three well studied metabolic proteins-lysozyme, bovine serum albumin (BSA) and ribonuclease A. Three classes of food additives- synthetic color, preservatives, and phosphate-containing, are taken here to understand their effects on the aforementioned metabolic proteins. Conventional molecular docking and dynamics (MD) studies reveal that these additives induce significant structural perturbations. Among them, carmoisine brings about the most secondary structural changes for lysozyme and ribonuclease A, whereas sodium tripolyphosphate affects BSA the most. To restore the secondary structural loss, we further examine the roles of osmolytes through cross-docking and higher timescale MD simulations. These studies unravel that application of osmolytes like raffinose and trehalose triggers structural restoration for BSA, lysozyme and ribonuclease A, and highlight their roles as co-formulants to alleviate the adverse effects of food additives.

Macromolecular crowding effects on the kinetics of opposing reactions catalyzed by alcohol dehydrogenase

In order to better understand how the complex, densely packed, heterogeneous milieu of a cell influences enzyme kinetics, we exposed opposing reactions catalyzed by yeast alcohol dehydrogenase (YADH) to both synthetic and protein crowders ranging from 10 to 550 kDa. The results reveal that the effects from macromolecular crowding depend on the direction of the reaction. The presence of the synthetic polymers, Ficoll and dextran, decrease V_max and K_m for ethanol oxidation. In contrast, these crowders have little effect or even increase these kinetic parameters for acetaldehyde reduction. This increase in V_max is likely due to excluded volume effects, which are partially counteracted by viscosity hindering release of the NAD⁺ product. Macromolecular crowding is further complicated by the presence of a depletion layer in solutions of dextran larger than YADH, which diminishes the hindrance from viscosity. The disparate effects from 25 g/L dextran or glucose compared to 25 g/L Ficoll or sucrose reveals that soft interactions must also be considered. Data from binary mixtures of glucose, dextran, and Ficoll support this “tuning” of opposing factors. While macromolecular crowding was originally proposed to influence proteins mainly through excluded volume effects, this work compliments the growing body of evidence revealing that other factors, such as preferential hydration, chemical interactions, and the presence of a depletion layer also contribute to the overall effect of crowding.

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Yeast alcohol dehydrogenase reduction of acetaldehyde is enhanced by crowding.

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Crowding effects on YADH kinetics depend on the direction of the reaction.

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Crowders like dextran can be used as a tool to elucidate enzyme mechanism.

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Excluded volume optimizes YADH hydride transfer; viscosity hinders product release.

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The presence of a depletion layer with large crowders mitigates their effects.

Oxidized Oligosaccharides Stabilize Rehydrated Sea Cucumbers against High-Temperature Impact

Small-molecule crosslinkers could diffuse into and stabilize protein hydrogels without damaging their appearance, but they are absent from the food industry due to the high safety and efficacy requirements for foods. Oxidized oligosaccharides are non-toxic small polyaldehydes previously found capable of crosslinking proteins by premixing. In this study, we managed to diffuse various oxidized oligosaccharides into the protein wall of rehydrated sea cucumbers, and the texture profile analysis, total soluble material assay and SEM (scanning electron microscope) images all suggested the treated sea cucumbers acquired significantly enhanced stability against high-temperature-promoted deterioration. The stabilization was positively correlated with the aldehyde content of oxidized oligosaccharides but negatively correlated with molecular size. The mechanism of stabilization was found to include both covalent and hydrogen bond crosslinking. These results have demonstrated that oxidized oligosaccharides could enter food protein hydrogel by free diffusion and stabilize the 3D network effectively and thereby has great potential in food-related industry.

Surface Behavior of BSA/Water/Carbohydrate Systems from Molecular Polarizability Measurements

The effect of the presence of glucose and sucrose on the nonintrinsic contribution to partial molar volume ⟨Θ⟩_ni of bovine serum albumin (BSA) is determined by means of static and dynamic electronic polarizability measurements. For that aim, a combined strategy based on high-resolution refractometry, high exactitude densitometry, and synchronous fluorescence spectroscopy is applied. Both static and dynamic mean electronic molecular polarizability values are found to be sensitive to the presence of glucose. In the case of sucrose, the polarizability of BSA is not appreciably affected. In fact, our results revealed that the electronic changes observed occurred without a modification of the native conformation of BSA. On the contrary, a nonmonotonous behavior with the concentration is observed in presence of glucose. These results advocate the influence of the electronic polarization on the repulsive and attractive protein-carbohydrate interactions. An analysis using the scaled particle theory indicates that the accumulation of glucose on the protein surface promotes dehydration. Inversely, hydration and preferential exclusion occur in the vicinity of the protein surface for sucrose-enriched systems.

Comparison of the thermal stabilization of proteins by oligosaccharides and monosaccharide mixtures: Measurement and analysis in the context of excluded volume theory

The thermal stability of apo α-lactalbumin (α-LA) and lysozyme was measured in the presence of mixtures of glucose, fructose, and galactose. Mixtures of these monosaccharides in the appropriate stoichiometric ratio were found to have a greater stabilizing effect on each of the two proteins than equal weight/volume concentrations of di- tri- and tetrasaccharides with identical subunit composition (sucrose, trehalose, raffinose, and stachyose). The excluded volume model for the effect of a single saccharide on the stability of a protein previously proposed by Beg et al. [Biochemistry 54 (2015) 3594] was extended to treat the case of saccharide mixtures. The extended model predicts quantitatively the stabilizing effect of all monosaccharide mixtures on α-LA and lysozyme reported here, as well as previously published results obtained for ribonuclease A [Biophys. Chem. 138 (2008) 120] to within experimental uncertainty.