Molecular mechanism of aspartame recognition by the human sweet taste receptor T1R2-T1R3 revealed by homology modeling and molecular dynamics simulations.

Aspartame is widely used as a noncaloric artificial sweetener in the food industry. Aspartame exists in two conformations, L-type and E-type, and its binding affinity to the T1R2 subunit of the human sweet taste receptor T1R2-T1R3 is highly susceptible to its conformational variability. In this study, homology modeling was performed using the GABAB receptor (PDB: 6UO8) as a template to construct four aspartame-T1R2-T1R3 complex models (E-type, L-D142E, L-S40T, and L-type). In addition, a coordinate alignment method was applied using the sucralose/human sweet taste receptor structure (PDB: 9UTB) as a template to generate five binding models (E-9UTB, L-9UTB, L-D142A, L-Y103A, and L-E302A). The results indicate that both L- and E-aspartame stably bind to T1R2-T1R3 and its mutants. Hydrogen bonding and hydrophobic interactions are identified as the primary contributors to the stable binding. Moreover, The L-type and L-E302A systems exhibited the highest stability, with binding free energies of - 15.85 kJ/mol and - 15.90 kJ/mol, respectively. Electrostatic interactions served as the driving force for the binding of L-type aspartame to the T1R2-T1R3 receptor and the E302A mutant receptor, with electrostatic energy contributions of - 25.70 kJ/mol and - 26.15 kJ/mol, respectively. Calculations of the binding pocket volume indicated that the D142E and D142A mutations induce slight steric hindrance or electronic effects, leading to an expansion of the binding cavity for L-type aspartame. Among the four models constructed using the GABAB receptor as a template, aspartame binding promoted the closure and stabilization of the Venus flytrap (VFT) domain in the T1R2 subunit. The findings of this study provide a theoretical basis for understanding the molecular mechanism of sweet taste perception and for guiding the rational design of novel sweeteners.