title: Differential roles of the C and N termini of Orai1 protein in interacting with stromal interaction molecule 1 (STIM1) for Ca2+ release-activated Ca2+ (CRAC) channel activation.
abstract: The entry of extracellular Ca(2+), which is mediated by Ca(2+) release-activated Ca(2+) (CRAC) channels, is essential for T cell activation and the normal functioning of other immune cells. Although the molecular components of CRAC channels, the Orai1 pore-forming subunit and the STIM1-activating subunit have been recently identified, the gating mechanism by which Orai1 channels conduct Ca(2+) entry upon Orai1-STIM1 interaction following Ca(2+) store release remains elusive. Herein, we show that C-terminal truncations or point mutations prevented Orai1 from binding to STIM1 and subsequent channel opening. In contrast, an Orai1 mutant with an N-terminal truncation interacted with but failed to be activated by STIM1. Moreover, Orai1 channels with C-terminal disruption, but not N-terminal truncation, could be gated by fused functional domains of STIM1. Interestingly, the channel activities of Orai1 mutants carrying either an N-terminal or a C-terminal truncation were restored by a methionine mutation at the putative gating hinge, the conserved Gly-98 site in the first transmembrane segment (TM1) of Orai1. Collectively, these results support a stepwise gating mechanism of STIM1-operated Orai1 channels; the initial binding between STIM1 and the C terminus of Orai1 docks STIM1 onto the N terminus of Orai1 to initiate conformational changes of the pore-lining TM1 helix of Orai1, leading to the opening of the channel.
authors: Department of Medical Physiology, College of Medicine, Texas A&M Health Science Center, Temple, Texas 76504, USA.
authors: Hongying
authors: H
authors: Zheng
authors: Meng-Hua
authors: MH
authors: Zhou
authors: Changlong
authors: C
authors: Hu
authors: Enoch
authors: E
authors: Kuo
authors: Xu
authors: X
authors: Peng
authors: Junjie
authors: J
authors: Hu
authors: Lih
authors: L
authors: Kuo
authors: Shenyuan L
authors: SL
authors: Zhang
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D000071740:ORAI1 Protein; D017433:Protein Structure, Secondary; 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