Bidirectional regulation of calcium release–activated calcium (CRAC) channel by SARAF

Abstract

Store-operated calcium entry (SOCE) through the Ca2+ release–activated Ca2+ (CRAC) channel is a central mechanism by which cells generate Ca2+ signals and mediate Ca2+-dependent gene expression. The molecular basis for CRAC channel regulation by the SOCE-associated regulatory factor (SARAF) remained insufficiently understood. Here we found that following ER Ca2+ depletion, SARAF facilitates a conformational change in the ER Ca2+ sensor STIM1 that relieves an activation constraint enforced by the STIM1 inactivation domain (ID; aa 475–483) and promotes initial activation of STIM1, its translocation to ER–plasma membrane junctions, and coupling to Orai1 channels. Following intracellular Ca2+ rise, cooperation between SARAF and the STIM1 ID controls CRAC channel slow Ca2+-dependent inactivation. We further show that in T lymphocytes, SARAF is required for proper T cell receptor evoked transcription. Taking all these data together, we uncover a dual regulatory role for SARAF during both activation and inactivation of CRAC channels and show that SARAF fine-tunes intracellular Ca2+ responses and downstream gene expression in cells.

A better brain? Alternative spliced STIM2 in hominoids arises with synapse formation and creates a gain-of-function variant

“…An increase in STIM1 function upon larger C-terminal deletion has recently been described for the TAM associated gain-of-function mutation STIM1 I484R , leading to termination of translation at residue 502, abrogating MT binding sites and PBD [42]. Here, interpretation of its activated phenotype involves a potential disabled binding of the inhibitory domain (ID) of STIM1 to the CC1 region and disabled binding of STIM1 to SARAF, an accessory protein which maintains STIM proteins in the closed and inactive conformation [43, 44], or a combination of both. Interaction of SARAF with STIM1 entails a second binding site encompassing residues 490 to 530 of STIM1 [45], a domain that shows only 15% conserved residues between STIM1 and STIM2, but is not altered in STIM2.3 compared to STIM2, thus we believe that the mechanism leading to STIM2.3’s increased function is likely independent of SARAF.…”

Photopharmacological modulation of native CRAC channels using azoboronate photoswitches

“…Total internal reflection fluorescence microscopy (TIRFM) was performed as described previously ( 70 ) using an inverted Olympus IX83 microscope combined with a cellTIRF-4Line system (405/488/561/640 nm lasers) and equipped with a back-illuminated scientific complementary metal oxide semiconductor (sCMOS) camera (Prime 95B, Photometrics). Fluorescence was collected by 100× (numerical aperture [N.A.]…”

Mutations in proteins involved in E-C coupling and SOCE and congenital myopathies

“…An additional regulator of SOCE is SARAF, an ER-resident protein that can exert activating and inactivating effects on CRAC channels by interacting with the SOAR domain or the inhibitory domain in STIM1 ( Palty et al, 2012 ; Dagan and Paltry, 2021 ; Zomot et al, 2021 ). Several other proteins interact and regulate SOCE, including STIMATE (STIM-activating enhancer; Lopez et al, 2016 ) and CASQ1, the main Ca 2+ buffer of the SR ( Shin et al, 2003 ; Zhang et al, 2016 ).…”