Fig. 5: Protonation of histidine residues modifies the binding affinity of saccharin. | Communications Biology

Fig. 5: Protonation of histidine residues modifies the binding affinity of saccharin.

From: Prediction of dynamic allostery for the transmembrane domain of the sweet taste receptor subunit, TAS1R3

Fig. 5

Saccharin was stably located in the binding pocket of human taste type 1 receptor member 3 (hTAS1R3) after a 500 ns molecular dynamics simulation at neutral pH (a) and at low pH (b). Left, overall view of the TAS1R3 bound with saccharin (Sac). Upper right, detailed view of the binding pocket of the Sac-bound TAS1R3 and the binding free energy (ΔGbind). Lower right, the molecular surface of the intracellular region of the Sac-bound TAS1R3 colored according to decomposition energy. Protonated histidine residues are indicated as HIP. ECL, extracellular loop. c–f The transmembrane domain (TMD) of hTAS1R3 mediates the pH-dependence of the sensitivity to Sac. HEK293 cells were transiently transfected with full-length and/or chimeric TAS1R2 and TAS1R3 as well as Gα16-gust44. The TAS1R2 (left) and TAS1R3 (right) are shown schematically. The full-length and chimeric TAS1Rs are labeled as human (h, red) or mouse (m, blue), with hm denoting the chimera containing the VFD and CRD of the human receptor coupled to the TMD of the mouse receptor, and mh indicating the chimera comprising the VFD and CRD of the mouse receptor coupled to the TMD of the human receptor. The responses of the receptors to different concentrations of Sac were examined at neutral pH (7.4) and at low pH (5.0). g, h Sac moved to the outside of the binding pocket of the hTAS1R3 variant at neutral or low pH during MD simulations. Overall views of the Sac-bound TAS1R3(H641AR725A) variant are shown at neutral pH (g) and low pH (h). i Mutation of hTAS1R3 attenuated the pH-dependence of the sensitivity to Sac. HEK293 cells were transiently transfected with TAS1R3 or TAS1R3(H641AR725A) together with TAS1R2 and Gα16-gust44. The responses of the receptors to different concentrations of Sac were examined at neutral pH (7.4) and low pH (5.0). Data are expressed as the mean ± S.E. of 15–20 cells (n = 3). *P < 0.05, **P < 0.01 for the comparison between neutral pH and low pH (two-way ANOVA and post-hoc t-test).

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