title: A calcium-accumulating region, CAR, in the channel Orai1 enhances Ca(2+) permeation and SOCE-induced gene transcription.
abstract: The Ca(2+) release-activated Ca(2+) channel mediates Ca(2+) influx in a plethora of cell types, thereby controlling diverse cellular functions. The channel complex is composed of stromal interaction molecule 1 (STIM1), an endoplasmic reticulum Ca(2+)-sensing protein, and Orai1, a plasma membrane Ca(2+) channel. Channels composed of STIM1 and Orai1 mediate Ca(2+) influx even at low extracellular Ca(2+) concentrations. We investigated whether the activity of Orai1 adapted to different environmental Ca(2+) concentrations. We used homology modeling and molecular dynamics simulations to predict the presence of an extracellular Ca(2+)-accumulating region (CAR) at the pore entrance of Orai1. Furthermore, simulations of Orai1 proteins with mutations in CAR, along with live-cell experiments, or simulations and electrophysiological recordings of the channel with transient, electrostatic loop3 interacting with loop1 (the site of CAR) determined that CAR enhanced Ca(2+) permeation most efficiently at low external Ca(2+) concentrations. Consistent with these results, cells expressing Orai1 CAR mutants exhibited impaired gene expression stimulated by the Ca(2+)-activated transcription factor nuclear factor of activated T cells (NFAT). We propose that the Orai1 channel architecture with a close proximity of CAR to the selectivity filter, which enables Ca(2+)-selective ion permeation, enhances the local extracellular Ca(2+) concentration to maintain Ca(2+)-dependent gene regulation even in environments with relatively low Ca(2+)concentrations.
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Irene
authors.initials: I
authors.lastname: Frischauf
authors.affiliation: Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.|Faculty of Sciences, University of South Bohemia, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.
authors.forename: Vasilina
authors.initials: V
authors.lastname: Zayats
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Deix
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.|Institute for Experimental and Clinical Cell Therapy, Paracelsus Medical University, A-5020 Salzburg, Austria.
authors.forename: Anna
authors.initials: A
authors.lastname: Hochreiter
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Isaac
authors.initials: I
authors.lastname: Jardin
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Muik
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Lackner
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.|Institute for Biophysics of Medical University Graz, A-8010, Graz, Austria.
authors.forename: Barbora
authors.initials: B
authors.lastname: Svobodová
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Teresa
authors.initials: T
authors.lastname: Pammer
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Monika
authors.initials: M
authors.lastname: Litviňuková
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Amrutha Arumbakam
authors.initials: AA
authors.lastname: Sridhar
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Isabella
authors.initials: I
authors.lastname: Derler
authors.affiliation: Department of Biophysics, School of Medicine, University of Saarland, D-66421 Homburg, Germany.
authors.forename: Ivan
authors.initials: I
authors.lastname: Bogeski
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Romanin
authors.affiliation: Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.|Faculty of Sciences, University of South Bohemia, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.
authors.forename: Rüdiger H
authors.initials: RH
authors.lastname: Ettrich
authors.affiliation: Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.
authors.forename: Rainer
authors.initials: R
authors.lastname: Schindl
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000502:physiology*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster; D057809:HEK293 Cells; D006801:Humans; D017136:Ion Transport / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000071740:ORAI1 Protein; D017433:Protein Structure, Secondary; D000071737:Stromal Interaction Molecule 1; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D000071740:ORAI1 Protein; C502662:Stim protein, Drosophila; D000071737:Stromal Interaction Molecule 1; C510747:olf186-F protein, Drosophila; D002118:Calcium