Fig. 1

Position of Asp⁵⁵² in a 3D model of the FMRFamide-gated Na⁺ channel, and fluorescence labeling of D552C with BODIPY TMR C₅-thiosulfate. a 3D model of the FMRFamide-gated Na⁺ channel. The model was made by use of Modeller, and the orientations of the side-chains were refined by use of SCWRL4. b Close up view of the wrist region of the channel. The inner cavity of the external vestibule, shown by transparent yellow, in the wrist region was detected by use of ALLCHANNELEXC, with probe radii of 10 \(\mathrm{\AA}\) for “shell volume” and 4 \(\mathrm{\AA}\) for “solvent-excluded volume” [25]. Side-chains of the three Asp⁵⁵²s are shown by use of stick models. c Fluorescence of water-injected, WT-expressing, or D552C-expressing oocyte after treatment with 100 μM BODIPY TMR C₅-thiosulfate for 2 min. The images show the fluorescence of the animal hemisphere of the oocytes 3 min after treatment. Scale bars indicate 300 μm