A pathogenic human Orai1 mutation unmasks STIM1-independent rapid inactivation of Orai1 channels.

Content Provider	Europe PMC
Author	Yeung, Priscilla S-W Yamashita, Megumi Prakriya, Murali
Editor	Trebak, Mohamed Aldrich, Richard W
Copyright Year	2023
Abstract	Ca2+ release-activated Ca2+ (CRAC) channels are activated by direct physical interactions between Orai1, the channel protein, and STIM1, the endoplasmic reticulum Ca2+ sensor. A hallmark of CRAC channels is fast Ca2+-dependent inactivation (CDI) which provides negative feedback to limit Ca2+ entry through CRAC channels. Although STIM1 is thought to be essential for CDI, its molecular mechanism remains largely unknown. Here, we examined a poorly understood gain-of-function (GOF) human Orai1 disease mutation, L138F, that causes tubular aggregate myopathy. Through pairwise mutational analysis, we determine that large amino acid substitutions at either L138 or the neighboring T92 locus located on the pore helix evoke highly Ca2+-selective currents in the absence of STIM1. We find that the GOF phenotype of the L138 pathogenic mutation arises due to steric clash between L138 and T92. Surprisingly, strongly activating L138 and T92 mutations showed CDI in the absence of STIM1, contradicting prevailing views that STIM1 is required for CDI. CDI of constitutively open T92W and L138F mutants showed enhanced intracellular Ca2+ sensitivity, which was normalized by re-adding STIM1 to the cells. Truncation of the Orai1 C-terminus reduced T92W CDI, indicating a key role for the Orai1 C-terminus for CDI. Overall, these results identify the molecular basis of a disease phenotype with broad implications for activation and inactivation of Orai1 channels.
Journal	eLife
Volume Number	12
PubMed Central reference number	PMC9991058
PubMed reference number	36806330
e-ISSN	2050084X
DOI	10.7554/elife.82281
Language	English
Publisher	eLife Sciences Publications, Ltd
Publisher Date	2023-02-20
Access Restriction	Open
Rights License	This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited. © 2023, Yeung, Yamashita et al
Subject Keyword	Orai1 STIM1 CRAC channels inactivation gating store-operated calcium entry Human
Content Type	Text
Resource Type	Article
Subject	Immunology and Microbiology Neuroscience Medicine Biochemistry, Genetics and Molecular Biology