Asn415 in the beta11-beta12 linker decreases proton-dependent desensitization of ASIC1

Neurons of the mammalian nervous system express the proton-sensing ion channel ASIC1. Low concentrations of protons in the normal range of extracellular pH, pH 7.4-7.3, shut the pore by a conformational transition referred as steady-state desensitization. Therefore, the potential of local acidification to open ASIC1 relies on proton affinity for desensitization. This property is important physiologically and also can be exploited to develop strategies to increase or decrease the channel response to protons. In a previous study (Li, T., Yang, Y., and Canessa, C. M. (2010) J. Biol. Chem. 285, 22706-22712), we found that Leu-85 in the β1-β2 linker of the extracellular domain decreases the apparent proton affinity for steady-state desensitization and retards openings, slowing down the time course of the macroscopic currents. Here, we show that Asn-415 in the β11-β12 linker works together with the β1-β2 linker to stabilize a closed conformation that delays transition from the closed to the desensitized state. Substitutions of Asn-415 for Cys, Ser, or Gly render ASIC1 responsive to small increases in proton concentrations near the baseline physiological pH.