The TAM-associated STIM1 mutation increases ORAI1 channel function due to a reduced STIM1 inactivation break and an absence of microtubule trapping.

Tubular aggregate myopathy (TAM) is a progressive skeletal muscle disease associated with gain-of-function mutations in the ER Ca sensor STIM1 that mediates store-operated Ca entry (SOCE) across the Ca-release-activated (CRAC) Ca channel ORAI1. A frameshift mutation in STIM1 inactivation domain, STIM1, was identified in a TAM patient and reported to decrease SOCE. Using ion imaging and electrophysiology, we show that the STIM1 mutation instead renders STIM1 constitutively active.

S-acylation by ZDHHC20 targets ORAI1 channels to lipid rafts for efficient Ca signaling by Jurkat T cell receptors at the immune synapse.

Efficient immune responses require Ca fluxes across ORAI1 channels during engagement of T cell receptors (TCR) at the immune synapse (IS) between T cells and antigen presenting cells. Here, we show that ZDHHC20-mediated S-acylation of the ORAI1 channel at residue Cys143 promotes TCR recruitment and signaling at the IS. Cys143 mutations reduced ORAI1 currents and store-operated Ca entry in HEK-293 cells and nearly abrogated long-lasting Ca elevations, NFATC1 translocation, and IL-2 secretion evoked by TCR engagement in Jurkat T cells.