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Binding Hotspot and Activation Mechanism of Maltitol and Lactitol toward the Human Sweet Taste Receptor

Mahalapbutr P, Lee VS, Rungrotmongkol T

J Agric Food Chem, 2020 Jul 29;68(30):7974-7983.
PMID: 32551626 DOI: 10.1021/acs.jafc.0c02580

Human sweet taste receptor (hSTR) recognizes a wide array of sweeteners, resulting in sweet taste perception. Maltitol and lactitol have been extensively used in place of sucrose due to their capability to prevent dental caries. Herein, several molecular modeling approaches were applied to investigate the structural and energetic properties of these two polyols/hSTR complexes. Triplicate 500 ns molecular dynamics (MD) simulations and molecular mechanics/generalized Born surface area (MM/GBSA)-based free energy calculations revealed that the TAS1R2 monomer is the preferential binding site for maltitol and lactitol rather than the TAS1R3 region. Several polar residues (D142, S144, Y215, D278, E302, R383, and especially N143) were involved in polyols binding through electrostatic attractions and H-bond formations. The molecular complexation process not only induced the stable form of ligands but also stimulated the conformational adaptation of the TAS1R2 monomer to become a close-packed structure through an induced-fit mechanism. Notably, the binding affinity of the maltitol/TAS1R2 complex (ΔGbind of -17.93 ± 1.49 kcal/mol) was significantly higher than that of the lactitol/TAS1R2 system (-8.53 ± 1.78 kcal/mol), in line with the experimental relative sweetness. These findings provide an in-depth understanding of the differences in the sweetness response between maltitol and lactitol, which could be helpful to design novel polyol derivatives with higher sweet taste perception.

Matched MeSH terms: Sugar Alcohols/chemistry
Effect of Various Polyols on the Acid-Denatured States of Champedak Galactose-Binding Lectin

Kameel NIA, Shuib AS, Tayyab S

Protein Pept Lett, 2018;25(3):314-324.
PMID: 29384048 DOI: 10.2174/0929866525666180130155007

BACKGROUND: Champedak galactose-binding (CGB) lectin is a tetrameric protein with noncovalently bound monomers, isolated from Artocarpus integer fruit seeds. We had previously reported existence of a structured monomer and an unfolded monomer of CGB lectin at pH 2.5 and pH 1.5, respectively. Polyols are known to induce significant refolding in denatured proteins and stabilize proteins against environmental stresses. Studies on the effect of various polyols on the acid-denatured states of CGB lectin are lacking.
OBJECTIVE: The objective of this study was to investigate the effects of four different polyols, namely, ethylene glycol, erythritol, xylitol and sorbitol on the acid-denatured states of CGB lectin.
METHODS: CGB lectin was subjected to acid denaturation at pH 2.5 and pH 1.5, both in the absence and presence of 30% (w/v) polyols, i.e. ethylene glycol, erythritol, xylitol and sorbitol. Thermal denaturation of the acid-denatured states was also studied in the absence and presence of these polyols. Different spectroscopic probes such as tryptophan fluorescence, ANS fluorescence and far-UV CD spectral signal were used to monitor structural changes in the acid-denatured states of CGB lectin in the presence of polyols.
RESULTS: Presence of erythritol, xylitol and sorbitol in the incubation mixture was found to stabilize the lectin at both pH 2.5 and pH 1.5, as evident from the burial of the hydrophobic clusters and decreased polarity around Trp residues. These polyols also stabilized the acid-denatured states of CGB lectin against thermal denaturation by shifting the thermal transition curves towards higher temperatures. Exposure of the acid-denatured states of CGB lectin, obtained at pH 2.5 and pH 1.5 to 61°C and 51°C, respectively, induced formation of non-native β-structures, compared to that present at 25°C, and this phenomenon was significantly suppressed in the presence of these polyols. Based on the spectral data, both sorbitol and erythritol appeared to exude better stabilizing effect. On the other hand, ethylene glycol was shown to destabilize the aciddenatured states of CGB lectin.
CONCLUSION: Thermal stabilization of the lectin was noticed in the presence of erythritol, xylitol and sorbitol at both pH 2.5 and pH 1.5. These polyols also stabilize the secondary and tertiary structures of the acid-denatured CGB lectin at 25°C. Ethylene glycol was proved to be a destabilizer of the acid-denatured CGB lectin.

Matched MeSH terms: Sugar Alcohols/chemistry*
Fulltext Purification and Characterization of Lipase Produced by Leuconostoc mesenteroides Subsp. mesenteroides ATCC 8293 Using an Aqueous Two-Phase System (ATPS) Composed of Triton X-100 and Maltitol

Eko Sukohidayat NH, Zarei M, Baharin BS, Manap MY

Molecules, 2018 Jul 20;23(7).
PMID: 30037038 DOI: 10.3390/molecules23071800

Purification of lipase produced by L. mesenteroides subsp. mesenteroides ATCC 8293 was conducted for the first time using a novel aqueous two-phase system (ATPS) composed of Triton X-100 and maltitol. The partitioning of lipase was optimized according to several parameters including pH, temperature, and crude load. Results showed that lipase preferentially migrated to the Triton X-100 rich phase and optimum lipase partitioning was achieved in ATPS at TLL of 46.4% and crude load of 20% at 30 °C and pH 8, resulting in high lipase purification factor of 17.28 and yield of 94.7%. The purified lipase showed a prominent band on SDS-PAGE with an estimated molecular weight of 50 kDa. The lipase was stable at the temperature range of 30⁻60 °C and pH range of 6⁻11, however, it revealed its optimum activity at the temperature of 37 °C and pH 8. Moreover, lipase exhibited enhanced activity in the presence of non-ionic surfactants with increased activity up to 40%. Furthermore, results exhibited that metals ions such as Na⁺, Mg2+, K⁺ and Ca2+ stimulated lipase activity. This study demonstrated that this novel system could be potentially used as an alternative to traditional ATPS for the purification and recovery of enzymes since the purified lipase still possesses good process characteristics after undergoing the purification process.

Matched MeSH terms: Sugar Alcohols/chemistry

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