Fig. 3: Transmembrane domain 3 (TM3) of MOR participated in the heteromerization of MOR and CCKBR.

a The computational predicted model of the MOR–CCKBR complex structure. The blue- and red-colored structures represent MOR and CCKBR, respectively. The green domains represent receptor–receptor-binding sites. b Expression and colocalization of MOR (TM3 replaced with TM6)-EGFP and CCKBR-mCherry in HEK293 cells. c FLIM images of EGFP alone or linked with mutant MOR or wild-type MOR in different overexpressing HEK293 cells. The lifetime of MOR-EGFP co-expressed with CCKBR-mCherry was shorter than that of MOR-EGFP expression alone, as indicated by a blueshift in the color. However, mutant MOR co-expressed with CCKBR-mCherry did not show significant blueshifting compared with the group expressing mutant MOR alone. d Statistics of EGFP fluorescence lifetime in (c). e FRET efficiency showed a significant decrease in energy transfer between mutant MOR-EGFP and CCKBR-mCherry. **p < 0.01, t-test. Data are represented as the mean ± SEM