Fig. 2.

Strategic labeling of NaChBac for ¹⁹F NMR determination of isoflurane-binding sites. (A) A side view and (B) top view of ¹⁹F-labeled residues. Colored residues shown in van der Waals presentation were mutated to cysteine individually and labeled with TET. Phenylalanine residues shown in gray lines were labeled with ¹⁹F in their side chains (the meta position). There are a total of 25 phenylalanine residues in each monomer with 13 in the voltage-sensing domain. Note that the ¹⁹F-labeled residues covered various regions of NaChBac: the extracellular surface (L179, S208), the selectivity filter (T189), the activation gate (F224, F227), the S4–S5 linker region (S129, L150), and the voltage-sensing domain.