Figure 6.

¹⁹F NMR detects Cl⁻ binding within the Cl⁻ permeation pathway and Cl⁻-dependent conformational change outside this region. (A) Cl⁻ induces a change in chemical environment of one or more tyrosine residues in the Buried Only protein at both pH 7.5 and 5.0. (B) Removal of fluorine labelling at the Y445 position abolishes the Cl⁻-dependent spectral effect at pH 5.0 (right panel) but not at pH 7.5 (left). (C) In the absence of Y419 labelling, Cl⁻-dependent spectral changes are observed at pH 7.5. (D) Removal of labelling at both the Y419 and Y445 positions eliminates the Cl⁻-dependent spectral changes at pH 7.5. (E) The ClC-ec1 Channel-like mutant (E148A/Y445S Buried Only) does not experience a Cl⁻-dependent spectral change at either pH.