Hydrophobic interactions of sucralose with protein structures

Induction of the Interdigitated Gel Phase of Hydrated Dipalmitoylphosphatidylcholine Bilayers by the Artificial Sweetener Sucralose

Recent research indicates that high doses of sucralose content can weaken the immune response in mice. To better understand the interaction between cell membranes and sucralose, we studied model biomembranes composed of dipalmitoylphosphatidylcholine bilayers in a sucralose solution. Calorimetry measurements showed that the effect of sucralose on the phase behavior is biphasic. Pretransitions and main transitions are decreased at low sucralose concentrations, while the main transition is increased at high concentrations. Pretransitions cannot be detected above the concentration at which the direction of change in the main transition temperature reverses. X-ray diffraction measurements revealed that sucralose at concentrations higher than 0.2 M induces the interdigitated gel (LβI) phase below the main transition temperature. Fluorescence Prodan measurements suggested that the sucralose solution is slightly more hydrophobic than the sucrose solution. This could be one reason why sucralose induces the LβI phase.

Biophysical Principles Emerging from Experiments on Protein-Protein Association and Aggregation

Protein-protein association and aggregation are fundamental processes that play critical roles in various biological phenomena, from cellular signaling to disease progression. Understanding the underlying biophysical principles governing these processes is crucial for elucidating their mechanisms and developing strategies for therapeutic intervention. In this review, we provide an overview of recent experimental studies focused on protein-protein association and aggregation. We explore the key biophysical factors that influence these processes, including protein structure, conformational dynamics, and intermolecular interactions. We discuss the effects of environmental conditions such as temperature, pH and related buffer-specific effects, and ionic strength and related ion-specific effects on protein aggregation. The effects of polymer crowders and sugars are also addressed. We list the techniques used to study aggregation. We analyze emerging trends and challenges in the field, including the development of computational models and the integration of multidisciplinary approaches for a comprehensive understanding of protein-protein association and aggregation.

The non-nutritive sweetener sucralose increases β-arrestin signaling at the constitutively active orphan G protein-coupled receptor GPR52

Non-nutritive sweeteners are popular food additives owing to their low caloric density and powerful sweetness relative to natural sugars. Their lack of metabolism contributes to evidence proclaiming their safety, yet several studies contradict this, demonstrating that sweeteners activate sweet taste G protein-coupled receptors (GPCRs) and elicit deleterious metabolic functions through unknown mechanisms. We hypothesize that activation of GPCRs, particularly orphan receptors due to their abundance in metabolically active tissues, contributes to the biological activity of sweeteners. We quantified the response of 64 orphans to the sweeteners saccharin and sucralose using a high-throughput β-arrestin-2 recruitment assay (PRESTO-Tango). GPR52 was the sole receptor that significantly responded to a mixture of sucralose and saccharin. Subsequent experiments revealed sucralose as the activating sweetener. Activation of GPR52 was concentration-dependent, with an EC50 of 0.23 mmol/L and an Emax of 3.43 ± 0.24 fold change at 4 mmol/L. GPR52 constitutively activates CRE pathways; however, we show that sucralose-induced activation of GPR52 does not further activate this pathway. Identification of this novel sucralose-GPCR interaction supports the notion that sucralose elicits off-target signaling through the activation of GPR52, calling into question sucralose's assumed lack of bioactivity.

Protein Preferential Solvation in (Sucralose + Water) Mixtures

Addition of sugars such as sucrose to aqueous protein solutions generally stabilizes proteins against thermal denaturation by preferential exclusion of sugars from proteins (preferential hydration of proteins). In this study, we investigated the effect of sucralose, a chlorinated sucrose derivative, on protein stability and preferential solvation. Circular dichroism and small-angle X-ray scattering measurements showed that sucrose increased the denaturation temperature of myoglobin and was preferentially excluded from the protein, whereas sucralose decreased the denaturation temperature of myoglobin and was preferentially adsorbed to the protein. No clear evidence was obtained for the indirect effects of sucralose on protein destabilization via the structure and properties of solvent water from the physicochemical properties (mass density, sound velocity, viscosity, and osmolality) of aqueous sucralose solutions; therefore, we concluded that a direct protein-sucralose interaction induced protein destabilization.

Aspect Ratio Modulation of Sucralose through {002}/{011} Preferred Orientation in Antisolvent Crystallization

The aspect ratio modulation in the alcoholysis process is highly significant for the production of high-quality sucralose. In this work, antisolvent crystallization (ASC) accompanied by preferred orientation was first adopted in the sucralose separation, based on which simultaneous modulations on aspect ratio, solubility, and stability have been realized. In detail, after the alcoholysis process in methanol, four antisolvents bearing different functional groups were used in ASC, i.e., isopentanol (IPN), isovaleraldehyde (IVD), isovaleric acid (IVA), and isobutyl propionate (IBP). To our interest, when IVA was used as the antisolvent, the highest separation efficiency (49.33%), fastest crystallizing rate (5.64%/h), lowest aspect ratio (1.55), and solubility (9.28 wt %) and good thermal stability (131.65 °C) of sucralose were achieved. Single crystal structures of sucralose using different antisolvents have been determined. Sucralose using IVA as the antisolvent exhibits the greatest molecular distortion and strongest intermolecular C-H···Cl hydrogen bonds; thus, the preferred growth along {002}/{011} directions has occurred and accounted for its lower aspect ratio, worse solubility, and better stability. The strongest methanol···IVA interactions due to the presence of a carboxyl group can accelerate the formation of the emulsion, resulting in the fastest crystallizing rate. The antisolvent screening and the discovery about relative mechanisms will provide a theoretical guide for the production of high-quality sucralose.

Unravelling structural, functional, evolutionary and genetic basis of SWEET transporters regulating abiotic stress tolerance in maize

Sugars Will Eventually be Exported Transporters (SWEETs) are the novel sugar transporters widely distributed among living systems. SWEETs play a crucial role in various bio-physiological processes, viz., plant developmental, nectar secretion, pollen development, and regulation of biotic and abiotic stresses, in addition to their prime sugar-transporting activity. Thus, in-depth structural, evolutionary, and functional characterization of maize SWEET transporters was performed for their utility in maize improvement. The mining of SWEET genes in the latest maize genome release (v.5) showed an uneven distribution of 20 ZmSWEETs. The comprehensive structural analyses and docking of ZmSWEETs with four sugars, viz., fructose, galactose, glucose, and sucrose, revealed frequent amino acid residues forming hydrogen (asparagine, valine, serine) and hydrophobic (tryptophan, glycine, and phenylalanine) interactions. Evolutionary analyses of SWEETs showed a mixed lineage with 50-100 % commonality of ortho-groups and -sequences evolved under strong purifying selection (Ka/Ks < 0.5). The duplication analysis showed non-functionalization (ZmSWEET18 in B73) and neo- and sub-functionalization (ZmSWEET3, ZmSWEET6, ZmSWEET9, ZmSWEET19, and ZmSWEET20) events in maize. Functional analyses of ZmSWEET genes through co-expression, in silico expression and qRT-PCR assays showed the relevance of ZmSWEETs expression in regulating drought, heat, and waterlogging stress tolerances in maize. The first ever ZmSWEET-regulatory network revealed 286 direct (ZmSWEET-TF: 140 ZmSWEET-miRNA: 146) and 1226 indirect (TF-TF: 597; TF-miRNA: 629) edges. The present investigation has given new insights into the complex transcriptional and post-transcriptional regulation and the regulatory and functional relevance of ZmSWEETs in assigning stress tolerance in maize.

Sucralose hydrogels: Peering into the reactivity of sucralose versus sucrose under lipase catalyzed trans-esterification

Sucralose differs from sucrose only by virtue of having three Cl groups instead of OH groups. Its intriguing features include being noncaloric, noncariogenic, ∼600 times sweeter than sucrose, stable at high temperatures/acidic pH's, and void of disagreeable aftertastes. These properties are attractive as food additive, one of which is as hydrogel obtainable via the technique of molecular gelation using a sucralose-derived low-molecular weight gelator (LMWG). Such hydrogels are highly responsive to external stimuli like temperature, because the LMWGs self-assemble via non-covalent interactions and could thus be utilized in applications like control-release. We found that sucralose to be unreactive under lipase biocatalysis, unlike sucrose. Hence, the aim of this work was (i) to use computational simulations to further understand sucralose's lack of enzymatic reactivity and (ii) to synthesize the sucralose-based amphiphiles using conventional chemical synthesis and systematically study their tendency towards hydrogelation. Sucrose and sucralose were docked with a high-resolution atomic structure of lipase B from Candida antarctica, modeling the esterification transition state with an active site serine. In extended molecular dynamics simulations, sucrose remained in the active site due to multiple sugar-protein hydrogen bonds. The oxygen-to-chlorine substitutions in sucralose disrupted this hydrogen bonding network. Consistent with observed lack of enzymatic conversion, in multiple simulations, sucralose would rapidly dissociate from the active site. The sucralose-based LMWGs were subsequently synthesized using base-catalyzed conventional chemical synthesis. Three of the sucralose-based amphiphiles (SL-5, SL-6 and SL-7) proved to be successful hydrogelators. The gelators also showed the ability to gel selected beverages. The LMWGs gelled quantities of water and beverage up to 71 and 55 times their weight, respectively, and remain thermally stable up to 144 °C.

Conformational Consequences for Compatible Osmolytes on Thermal Denaturation

Compatible osmolytes are a broad class of small organic molecules employed by living systems to combat environmental stress by enhancing the native protein structure. The molecular features that make for a superior biopreservation remain elusive. Through the use of time-resolved and steady-state spectroscopic techniques, in combination with molecular simulation, insight into what makes one molecule a more effective compatible osmolyte can be gained. Disaccharides differing only in their glycosidic bonds can exhibit different degrees of stabilization against thermal denaturation. The degree to which each sugar is preferentially excluded may explain these differences. The present work examines the biopreservation and hydration of trehalose, maltose, and gentiobiose.

Chronic consumption of sweeteners in mice and its effect on the immune system and the small intestine microbiota

Introduction: Sweeteners are additives used in different foods. They can be natural (sucrose and stevia) or artificial (sucralose). Currently, they are routinely consumed in multiple products and their effects on the mucosa of the small intestine and its microbiota are still controversial. Objective: To relate the consumption of sweeteners and their effect on the immune system and the microbiota of the small intestine in CD1 mice. Materials and methods: We used 54 three-week-old CD1 mice divided into three groups in the experiments: 1) A group of three weeks without treatment, 2) a group treated for six weeks, and 3) a group treated for 12 weeks using sucrose, sucralose, and stevia. We obtained CD19+ B lymphocytes, IgA+ antibodies, transforming growth factor-beta (TGF-b), and interleukins 12 and 17 (IL-12 and -17) from Peyer’s patches and lamina propria cells while DNA was obtained from intestinal solids to identify bacterial species. Results: After 12 weeks, sucrose and sucralose consumption caused a reduction in bacterial communities with an increase in CD19+, a decrease in IgA+ and TGF-b, and an increase in IL-12 and -17 in the Peyer’s patches while in the lamina propria there was an increase in all parameters. In contrast, stevia led to an improvement in bacterial diversity and percentage of CD19+ lymphocytes with minimal increase in IgA+, TGF-b, and IL-12, and a decrease in IL-17. Conclusion: Sucrose and sucralose caused negative alterations in bacterial diversity and immune parameters after 12 weeks; in contrast, stevia was beneficial for the intestinal mucosa.

Mechanistic differences in the effects of sucrose and sucralose on the phase stability of lysozyme solutions

The effect of two disaccharide analogues, sucrose and sucralose, on the phase stability of aqueous lysozyme solutions has been addressed from a mechanistic viewpoint by a combination of experiment and molecular dynamics (MD) simulations. The influence of the added low molecular weight salts (NaBr, NaI and NaNO₃) was considered as well. The cloud-point temperature measurements revealed a larger stabilizing effect of sucralose. Upon increasing sugar concentration, the protein solutions became more stable and differences in the effect of sucralose and sucrose amplified. It was confirmed that the addition of either of the two sugars imposed no secondary structure changes of the lysozyme. Enthalpies of lysozyme-sugar mixing were exothermic and a larger effect was recorded for sucralose. MD simulations indicated that acidic, basic and polar amino acid residues play predominant roles in the sugar-protein interactions, mainly through hydrogen bonding. Such sugar mediated protein-protein interactions are thought to be responsible for the biopreserative nature of sugars. Our observations hint at mechanistic differences in sugar-lysozyme interactions: while sucrose does not interact directly with the protein's surface for the most part (in line with the preferential hydration hypothesis), sucralose forms hydrogen bonds with acidic, basic and polar amino acid residues at the lysozyme's surface (in line with the water replacement hypothesis).

Hydration Dynamics in Solutions of Cyclic Polyhydroxyl Osmolytes

Simple sugars are remarkably effective at preserving protein and enzymatic structures against thermal and hydrostatic stress. Here, we investigate the hydrodynamic and biopreservative properties of three small cyclic molecules: glucose, myo-inositol, and methyl-α-d-glucopyranoside using circular dichroism spectroscopy and isothermal calorimetry. Using ultrafast fluorescence frequency upconversion spectroscopy, we measure the dynamical retardation of hydration dynamics in cosolute solutions. We find that all three molecules are effective modifiers of hydration dynamics in solution and all are also effective at protecting model protein systems against thermal denaturation. Methyl-α-d-glucopyranoside is found to be the most effective dynamic reducer displaying an approximately 30% increase in solvation relaxation time as compared to water in a cosolute free solution. myo-Inositol and glucose both exhibit a smaller reduction in dynamics with similar magnitudes of concentration dependence. Using these cosolute models, we demonstrate that the thermal enhancement of protein structure does not correlate strongly with either the dynamical reduction of the bulk solution nor with the number of hydrogen bonds a cosolute makes with the solvent. Furthermore, solutions of glucose at twice the concentration of trehalose are shown to have similar magnitudes of dynamical impact. This implies that regulation of hydration dynamics is not a distinguishing characteristic of successful osmolytes. This work highlights the need for further studies and computational analysis to understand the phenomena of preferential exclusion and the contribution of hydration dynamics to protein structural stability.

Stochastic Binding Process of Blunt-End Stacking of DNA Molecules Observed by Atomic Force Microscopy

Hydrophobic attraction is often a physical origin of nonspecific and irreversible (uncontrollable) processes observed for colloidal and biological systems, such as aggregation, precipitation, and fouling with biomolecules. On the contrary, blunt-end stacking of complementary DNA duplex chain pairs, which is also mainly driven by hydrophobic interaction, is specific and stable enough to lead to self-assemblies of DNA nanostructures. To understand the reason behind these contradicting phenomena, we measured forces operating between two self-assembled monolayers of duplexed DNA molecules with blunt ends (DNA-SAMs) and analyzed their statistics. We found the high specificity and stability of blunt-end stacking that resulted in the high resemblance between the interaction forces measured on approaching and retracting. The other finding is on the stochastic formation process of blunt-end stacking, which appeared as a significant fluctuation of the interaction forces at separations smaller than 2.5 nm. Based on these results, we discuss the underlying mechanism of the specificity and stability of blunt-end stacking.

Sweet Binders: Carbonic Anhydrase IX in Complex with Sucralose

Carbonic anhydrase IX (CA IX) expression is important for the regulation of pH in hypoxic tumors and is emerging as a therapeutic target for the treatment of various cancers. Recent studies have demonstrated the selectivity of sucrose, saccharin, and acesulfame potassium for CA IX over other CA isoforms. Reported here is the X-ray crystal structure of CA IX-mimic in complex with sucralose determined to ∼1.5 Å resolution. Furthermore, this structure is compared to the aforementioned sweetener/carbohydrate structural studies in order to determine active site properties of CA IX that promote selective binding. This structural analysis provides a further understanding of CA IX isoform specific inhibition to facilitate the design of new inhibitors and anticancer drugs.