title: STIM1 dimers undergo unimolecular coupling to activate Orai1 channels.
abstract: The endoplasmic reticulum (ER) Ca(2+) sensor, STIM1, becomes activated when ER-stored Ca(2+) is depleted and translocates into ER-plasma membrane junctions where it tethers and activates Orai1 Ca(2+) entry channels. The dimeric STIM1 protein contains a small STIM-Orai-activating region (SOAR)--the minimal sequence sufficient to activate Orai1 channels. Since SOAR itself is a dimer, we constructed SOAR concatemer-dimers and introduced mutations at F394, which is critical for Orai1 coupling and activation. The F394H mutation in both SOAR monomers completely blocks dimer function, but F394H introduced in only one of the dimeric SOAR monomers has no effect on Orai1 binding or activation. This reveals an unexpected unimolecular coupling between STIM1 and Orai1 and argues against recent evidence suggesting dimeric interaction between STIM1 and two adjacent Orai1 channel subunits. The model predicts that STIM1 dimers may be involved in crosslinking between Orai1 channels with implications for the kinetics and localization of Orai1 channel opening.
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Yandong
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Xizhuo
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Xianming
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Loktionova
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Xiangyu
authors.initials: X
authors.lastname: Cai
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Nwokonko
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Vrana
authors.affiliation: Beijing Key Department of Genetics and Developmental Biology, College of Life Sciences, Beijing Normal University, Beijing 100875, China.
authors.forename: Youjun
authors.identifier: http://orcid.org/0000-0003-0961-1716
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Brad S
authors.identifier: http://orcid.org/0000-0003-1982-2269
authors.initials: BS
authors.lastname: Rothberg
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Gill
mesh_terms: D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002850:Chromatography, Gel; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D000071740:ORAI1 Protein; D018408:Patch-Clamp Techniques; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary; D000071737:Stromal Interaction Molecule 1
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; D002118:Calcium