title: Glu¹⁰⁶ in the Orai1 pore contributes to fast Ca²⁺-dependent inactivation and pH dependence of Ca²⁺ release-activated Ca²⁺ (CRAC) current.
abstract: FCDI (fast Ca²⁺-dependent inactivation) is a mechanism that limits Ca²⁺ entry through Ca²⁺ channels, including CRAC (Ca²⁺ release-activated Ca²⁺) channels. This phenomenon occurs when the Ca²⁺ 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⁺ sensor that communicates the Ca²⁺ load of the intracellular stores to Orai1, have been shown to regulate fast Ca²⁺-dependent inactivation. Although significant advances in unravelling the mechanisms of CRAC channel gating have occurred, the mechanisms regulating fast Ca²⁺-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⁺-binding site that regulates fast Ca²⁺-dependent inactivation, whereas the V102I and E190Q mutants when expressed at appropriate ratios with STIM1 have fast Ca²⁺-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⁺ permeation through the E106D Orai1 pore by Ca²⁺ is diminished. These results suggest that Glu¹⁰⁶ inside the CRAC channel pore is involved in co-ordinating the Ca²⁺-binding site that mediates fast Ca²⁺-dependent inactivation.
authors.affiliation: School of Medical Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.
authors.forename: Nathan R
authors.initials: NR
authors.lastname: Scrimgeour
authors.forename: David P
authors.initials: DP
authors.lastname: Wilson
authors.forename: Grigori Y
authors.initials: GY
authors.lastname: Rychkov
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D018698:Glutamic Acid / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D008565:Membrane Proteins / Q000096:biosynthesis; D009363:Neoplasm Proteins / Q000096:biosynthesis; D000071740:ORAI1 Protein; D018408:Patch-Clamp Techniques; D051381:Rats; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C532493:Orai1 protein, rat; C103530:STIM1 protein, human; C518857:Stim1 protein, rat; D000071737:Stromal Interaction Molecule 1; D018698:Glutamic Acid; D002118:Calcium