title: STIM1 couples to ORAI1 via an intramolecular transition into an extended conformation.
abstract: Stromal interaction molecule (STIM1) and ORAI1 are key components of the Ca(2+) release-activated Ca(2+) (CRAC) current having an important role in T-cell activation and mast cell degranulation. CRAC channel activation occurs via physical interaction of ORAI1 with STIM1 when endoplasmic reticulum Ca(2+) stores are depleted. Here we show, utilizing a novel STIM1-derived Förster resonance energy transfer sensor, that the ORAI1 activating small fragment (OASF) undergoes a C-terminal, intramolecular transition into an extended conformation when activating ORAI1. The C-terminal rearrangement of STIM1 does not require a functional CRAC channel, suggesting interaction with ORAI1 as sufficient for this conformational switch. Extended conformations were also engineered by mutations within the first and third coiled-coil domains in the cytosolic portion of STIM1 revealing the involvement of hydrophobic residues in the intramolecular transition. Corresponding full-length STIM1 mutants exhibited enhanced interaction with ORAI1 inducing constitutive CRAC currents, even in the absence of store depletion. We suggest that these mutant STIM1 proteins imitate a physiological activated state, which mimics the intramolecular transition that occurs in native STIM1 upon store depletion.
authors.affiliation: Institute of Biophysics, University of Linz, Linz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Muik
authors.forename: Marc
authors.initials: M
authors.lastname: Fahrner
authors.forename: Rainer
authors.initials: R
authors.lastname: Schindl
authors.forename: Peter
authors.initials: P
authors.lastname: Stathopulos
authors.forename: Irene
authors.initials: I
authors.lastname: Frischauf
authors.forename: Isabella
authors.initials: I
authors.lastname: Derler
authors.forename: Peter
authors.initials: P
authors.lastname: Plenk
authors.forename: Barbara
authors.initials: B
authors.lastname: Lackner
authors.forename: Klaus
authors.initials: K
authors.lastname: Groschner
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Ikura
authors.forename: Christoph
authors.initials: C
authors.lastname: Romanin
mesh_terms: D015153:Blotting, Western; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004594:Electrophysiology; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D000071740:ORAI1 Protein; D011487:Protein Conformation; D000071737:Stromal Interaction Molecule 1; D014162:Transfection
chemical_list: D015220:Calcium Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1