Figure 4.

Anions mediate binding of alanine, serine and methionine. (A) Electron density omit map contoured at 5 σ for alanine, six water molecules, and a Cl⁻ ion trapped in the AvGluR1 ligand binding cavity; coloring and water numbering is the same as for Figure 3. (B) Shows the equivalent view for the serine complex; note the different position of the Cl⁻ ion and displacement of W7. (C) Equivalent view for the methionine complex. (D) Equivalent view for the phenylalanine complex. (E) Equilibrium dose inhibition curves for displacement of 100 nM [³H] L-Glu by glutamate and aspartate in the absence of Cl⁻; curves for control responses, taken from Figure 1, are plotted as dashed lines. (F) Equilibrium dose inhibition curves for alanine, serine and methionine; note the large rightward shift in in the absence of Cl⁻.