Figure 5. Proton binding site of ASIC1. Three close carboxy- carboxylate interactions, Asp238-Asp350 (red), Glu239-Asp346 (blue), and Glu220-Asp408 (yellow), form the acidic pocket that recognizes and binds protons. The interactions between these amino acid pairs are 2.8-3.0 Å. PDB ascession code: 2QTS.