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

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.