title: Atomic force microscopy (AFM) imaging suggests that stromal interaction molecule 1 (STIM1) binds to Orai1 with sixfold symmetry.
abstract: Depletion of Ca(2+) from the endoplasmic reticulum (ER) lumen triggers the opening of Ca(2+) release-activated Ca(2+) (CRAC) channels at the plasma membrane. CRAC channels are activated by stromal interaction molecule 1 (STIM1), an ER resident protein that senses Ca(2+) store depletion and interacts with Orai1, the pore-forming subunit of the channel. The subunit stoichiometry of the CRAC channel is controversial. Here we provide evidence, using atomic force microscopy (AFM) imaging, that Orai1 assembles as a hexamer, and that STIM1 binds to Orai1 with sixfold symmetry. STIM1 associates with Orai1 in the form of monomers, dimers, and multimeric string-like structures that form links between the Orai1 hexamers. Our results provide new insights into the nature of the interactions between STIM1 and Orai1.
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom.
authors.forename: Dilshan
authors.initials: D
authors.lastname: Balasuriya
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom.
authors.forename: Shyam
authors.initials: S
authors.lastname: Srivats
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom.
authors.forename: Ruth D
authors.initials: RD
authors.lastname: Murrell-Lagnado
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom. Electronic address: jme1000@cam.ac.uk.
authors.forename: J Michael
authors.initials: JM
authors.lastname: Edwardson
mesh_terms: D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000378:metabolism*; D000071740:ORAI1 Protein; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; 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
keywords: Atomic force microscopy; CRAC channel; Orai1; STIM1; Store-operated Ca(2+) entry