Interhelical interactions within the STIM1 CC1 domain modulate CRAC channel activation

The calcium release activated calcium (CRAC) channel is activated by the endoplasmic reticulum-resident calcium sensor protein STIM1. Upon activation, STIM1 C-terminus changes from an inactive, tight to an active, extended conformation. A coiled-coil (CC) clamp involving the CC1 and CC3 domains is essential in controlling STIM1 activation, with CC1 as key entity. The NMR-derived solution structure of the CC1 domain represents a three-helix bundle stabilized by interhelical contacts, which are absent in the Stormorken disease-related STIM1 R304W mutant. Two interhelical sites between CC1α(1) and CC1α(2) helices are key in controlling STIM1 activation, affecting the balance between tight and extended conformations. NMR-directed mutations within these interhelical interactions restore the physiological, store-dependent activation behavior of the gain-of-function STIM1 R304W mutant. This study reveals the functional impact of interhelical interactions within the CC1 domain for modifying the CC1-CC3 clamp strength to control the activation of STIM1.