STIM1/Orai1 coiled-coil interplay in the regulation of store-operated calcium entry

• Published in: Nature communications Vol. 4; no. 1; p. 2963
• Main Authors: Stathopulos, Peter B, Schindl, Rainer, Fahrner, Marc, Zheng, Le, Gasmi-Seabrook, Geneviève M, Muik, Martin, Romanin, Christoph, Ikura, Mitsuhiko
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 19.12.2013; Nature Pub. Group
• Subjects: Amino Acid Sequence; Calcium - metabolism; Calcium Channels - metabolism; Cytosol - metabolism; Dimerization; Endoplasmic Reticulum - metabolism; HEK293 Cells; Humans; Magnetic Resonance Spectroscopy; Membrane Proteins - metabolism; Molecular Conformation; Molecular Sequence Data; Mutagenesis; Mutation; Neoplasm Proteins - metabolism; ORAI1 Protein; Patch-Clamp Techniques; Stromal Interaction Molecule 1
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3963

Orai1 calcium channels in the plasma membrane are activated by stromal interaction molecule-1 (STIM1), an endoplasmic reticulum calcium sensor, to mediate store-operated calcium entry (SOCE). The cytosolic region of STIM1 contains a long putative coiled-coil (CC)1 segment and shorter CC2 and CC3 domains. Here we present solution nuclear magnetic resonance structures of a trypsin-resistant CC1-CC2 fragment in the apo and Orai1-bound states. Each CC1-CC2 subunit forms a U-shaped structure that homodimerizes through antiparallel interactions between equivalent α-helices. The CC2:CC2' helix pair clamps two identical acidic Orai1 C-terminal helices at opposite ends of a hydrophobic/basic STIM-Orai association pocket. STIM1 mutants disrupting CC1:CC1' interactions attenuate, while variants promoting CC1 stability spontaneously activate Orai1 currents. CC2 mutations cause remarkable variability in Orai1 activation because of a dual function in binding Orai1 and autoinhibiting STIM1 oligomerization via interactions with CC3. We conclude that SOCE is activated through dynamic interplay between STIM1 and Orai1 helices.