The STIM-Orai pathway: Conformational coupling between STIM and Orai in the activation of store-operated Ca2+ entry

Robert M. Nwokonko, Xiangyu Cai, Natalia A. Loktionova, Youjun Wang, Yandong Zhou, Donald L. Gill

Research output: Chapter in Book/Report/Conference proceedingChapter

12 Scopus citations

Abstract

Store-operated Ca2+ entry fulfills a crucial role in controlling Ca2+ signals in almost all cells. The Ca2+-sensing stromal interaction molecule (STIM) proteins in the endoplasmic reticulum (ER) undergo complex conformational changes in response to depleted ER luminal Ca2+, allowing them to unfold and become trapped in ER-plasma membrane (PM) junctions. Dimers of STIM proteins trap and gate the plasma membrane Orai Ca2+ channels within these junctions to generate discrete zones of high Ca2+ and regulate sensitive Ca2+-dependent intracellular signaling pathways. The STIM-Orai activating region (SOAR) of STIM1 becomes exposed upon store depletion and promotes trapping of Orai1 at the PM. Residue Phe-394 within SOAR forms an integral part of the high-affinity Orai1-interacting site. Our results demonstrate that only a single active site within the dimeric SOAR domain of STIM1 is required for the activation of Orai1 channel activity. This unimolecular model is strongly supported by evidence of variable STIM1:Orai1 stoichiometry reported in many studies. We hypothesize that unimolecular coupling promotes cross-linking of channels, localizing Ca2+ signals, and regulating channel activity. We have also identified a key “nexus” region in Orai1 near the C-terminal STIM1-binding site that can be mutated to constitutively activate Ca2+ entry, mimicking STIM1 activated channels. This suggests that STIM1 mediates gating of Orai1 in an allosteric manner via interaction with the Orai1 C-terminus alone. This model suggests the dual role of STIM1 in regulating both localization and gating of Orai1 channels and has important implications for the regulation of SOCE-mediated downstream signaling and the kinetics of channel activation.

Original languageEnglish (US)
Title of host publicationAdvances in Experimental Medicine and Biology
PublisherSpringer New York LLC
Pages83-98
Number of pages16
DOIs
StatePublished - 2017

Publication series

NameAdvances in Experimental Medicine and Biology
Volume993
ISSN (Print)0065-2598
ISSN (Electronic)2214-8019

All Science Journal Classification (ASJC) codes

  • Biochemistry, Genetics and Molecular Biology(all)

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