The STIM1-binding site nexus remotely controls Orai1 channel gating.

Yandong Zhou,Brad S Rothberg,Robert M Nwokonko,Xiangyu Cai,Donald L Gill,Xizhuo Wang,Natalia A Loktionova,Mohamed Trebak,Youjun Wang,Xianming Wang

doi:10.1038/ncomms13725

Yandong Zhou, Brad S Rothberg + Show 8 more

Open Access

https://doi.org/10.1038/ncomms13725

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Abstract

The ubiquitously expressed Orai Ca2+ channels are gated through a unique process of intermembrane coupling with the Ca2+-sensing STIM proteins. Despite the significance of Orai1-mediated Ca2+ signals, how gating of Orai1 is triggered by STIM1 remains unknown. A widely held gating model invokes STIM1 binding directly to Orai1 pore-forming helix. Here we report that an Orai1 C-terminal STIM1-binding site, situated far from the N-terminal pore helix, alone provides the trigger that is necessary and sufficient for channel gating. We identify a critical ‘nexus' within Orai1 connecting the peripheral C-terminal STIM1-binding site to the Orai1 core helices. Mutation of the nexus transforms Orai1 into a persistently open state exactly mimicking the action of STIM1. We suggest that the Orai1 nexus transduces the STIM1-binding signal through a conformational change in the inner core helices, and that STIM1 remotely gates the Orai1 channel without the necessity for direct STIM1 contact with the pore-forming helix.

Highlights

The ubiquitously expressed Orai Ca2 þ channels are gated through a unique process of intermembrane coupling with the Ca2 þ -sensing stromal interaction molecule (STIM) proteins
The results reveal that the Orai1-ANSGA mutant mediates authentic, constitutive ICRAC, indistinguishable from Ca2 þ -release-activated Ca2 þ (CRAC) current mediated by Orai1-WT in response to STIM1
We focused on three residues (L81, S82 and K85) oriented outward from the M1 extension (M1-ext) helix (Fig. 6a) and recently reported as the N-terminal binding site required for STIM1 mediating Orai[1] channel gating[12]

Summary

Introduction

The ubiquitously expressed Orai Ca2 þ channels are gated through a unique process of intermembrane coupling with the Ca2 þ -sensing STIM proteins. We suggest that the Orai[1] nexus transduces the STIM1-binding signal through a conformational change in the inner core helices, and that STIM1 remotely gates the Orai[1] channel without the necessity for direct STIM1 contact with the pore-forming helix. The widely expressed Orai family of plasma membrane (PM) Ca2 þ entry channels are gated by the endoplasmic reticulum (ER) Ca2 þ sensing stromal interaction molecule (STIM) proteins through a unique intermembrane conformational coupling mechanism[1,2,3]. Our studies militate against the widely held two-site gating model involving direct STIM1 binding to the N-terminal pore-forming helix to open the channel[7,9,10,11,12,13,14,15,16,17]. We present evidence that the nexus functions as a STIM1-triggered conformational switch that ‘remotely controls’ Orai[1] channel gating through internal helical interactions leading to opening of the pore mouth

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Conclusion