title: Tetrameric Orai1 is a teardrop-shaped molecule with a long, tapered cytoplasmic domain.
abstract: The Ca(2+) release-activated Ca(2+) channel is a principal regulator of intracellular Ca(2+) rise, which conducts various biological functions, including immune responses. This channel, involved in store-operated Ca(2+) influx, is believed to be composed of at least two major components. Orai1 has a putative channel pore and locates in the plasma membrane, and STIM1 is a sensor for luminal Ca(2+) store depletion in the endoplasmic reticulum membrane. Here we have purified the FLAG-fused Orai1 protein, determined its tetrameric stoichiometry, and reconstructed its three-dimensional structure at 21-A resolution from 3681 automatically selected particle images, taken with an electron microscope. This first structural depiction of a member of the Orai family shows an elongated teardrop-shape 150A in height and 95A in width. Antibody decoration and volume estimation from the amino acid sequence indicate that the widest transmembrane domain is located between the round extracellular domain and the tapered cytoplasmic domain. The cytoplasmic length of 100A is sufficient for direct association with STIM1. Orifices close to the extracellular and intracellular membrane surfaces of Orai1 seem to connect outside the molecule to large internal cavities.
authors.affiliation: Neuroscience Research Institute and National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568.
authors.forename: Yuusuke
authors.initials: Y
authors.lastname: Maruyama
authors.affiliation: Neuroscience Research Institute and National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568; Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ogura
authors.affiliation: Neuroscience Research Institute and National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568; Biomedicinal Information Research Center, National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Mio
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Kato
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kaneko
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kiyonaka
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Mori
authors.affiliation: Neuroscience Research Institute and National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568; Biomedicinal Information Research Center, National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568. Electronic address: ti-sato@aist.go.jp.
authors.forename: Chikara
authors.initials: C
authors.lastname: Sato
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism; D000071740:ORAI1 Protein; D020836:Protein Structure, Quaternary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C520430:Orai1 protein, mouse; C103530:STIM1 protein, human; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1; D002118:Calcium