Glu106 in the Orai1 pore contributes to fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation and pH dependence of Ca2[SUPERSCRIPT PLUS SIGN] release-activated Ca2[SUPERSCRIPT PLUS SIGN] (CRAC) current.

摘要

FCDI (fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation) is a mechanism that limits Ca2[SUPERSCRIPT PLUS SIGN] entry through Ca2[SUPERSCRIPT PLUS SIGN] channels, including CRAC (Ca2[SUPERSCRIPT PLUS SIGN] release-activated Ca2[SUPERSCRIPT PLUS SIGN]) channels. This phenomenon occurs when the Ca2[SUPERSCRIPT PLUS SIGN] concentration rises beyond a certain level in the vicinity of the intracellular mouth of the channel pore. In CRAC channels, several regions of the pore-forming protein Orai1, and STIM1 (stromal interaction molecule 1), the sarcoplasmic/endoplasmic reticulum Ca2[SUPERSCRIPT PLUS SIGN] sensor that communicates the Ca2[SUPERSCRIPT PLUS SIGN] load of the intracellular stores to Orai1, have been shown to regulate fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation. Although significant advances in unravelling the mechanisms of CRAC channel gating have occurred, the mechanisms regulating fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation in this channel are not well understood. We have identified that a pore mutation, E106D Orai1, changes the kinetics and voltage dependence of the ICRAC (CRAC current), and the selectivity of the Ca2[SUPERSCRIPT PLUS SIGN]-binding site that regulates fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation, whereas the V102I and E190Q mutants when expressed at appropriate ratios with STIM1 have fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation similar to that of WT (wild-type) Orai1. Unexpectedly, the E106D mutation also changes the pH dependence of ICRAC. Unlike WT ICRAC, E106D-mediated current is not inhibited at low pH, but instead the block of Na[SUPERSCRIPT PLUS SIGN] permeation through the E106D Orai1 pore by Ca2[SUPERSCRIPT PLUS SIGN] is diminished. These results suggest that Glu106 inside the CRAC channel pore is involved in co-ordinating the Ca2[SUPERSCRIPT PLUS SIGN]-binding site that mediates fast Ca2[SUPERSCRIPT PLUS SIGN]-dependent inactivation.