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. 2021 Feb 12;12:984. doi: 10.1038/s41467-021-21262-9

Fig. 3. Protonation state of His297 is influenced by fentanyl binding.

Fig. 3

ac Occupancies of the HID (green), HIE (orange), and HIP (blue) states of His297 as a function of pH from the replica-exchange CpHMD simulations of the apo mOR (a) and fentanyl-bound complex in the D147- (b) and H297-binding mode (c). The three states are in equilibrium through protonation/deprotonation and tautomerization. d Average distance between the piperidine nitrogen and His297’s Nϵ at different pH conditions when His297 is in the HID (green), HIE (orange), or HIP (blue) state. The area of the data point is proportional to the occupancy of the protonation state. A zoomed-in snapshot corresponding to the HID state is shown.