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.

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Print) 1362-3028 (Online) Journal homepage: http://www.tandfonline.com/loi/tmph20 31 P and 13 C chemical shielding tensors in the phosphoenolpyruvate moiety from rotary resonance recoupling 13 C and 31 P MAS and single crystal 31 A 31P and I3C NMR study of powder and single crystal samples of two phosphoenolpyruvate (PEP) compounds, the tris-ammonium salt monohydrate NH4)3(PEP).H20 (l), and the mono-ammonium-salt (NH4)(H,PEP) (2) is presented. The A P chemical shielding tensors in 1 are measured by 31P single crystal NMR on four minuscule samples and assigned without ambiguity by exploiting the orientation-dependent 31P-31P dipolar splittings of the resonance lines. The orientation of the 31P chemical shielding tensor is discussed in terms of the C2"-and C3-type distortions of the phosphate P04-coordination sphere. From I3C MAS NMR experiments with 31P rotary resonance recoupling on polycrystalline powder samples the orientations of the 31P chemical shielding tensors in l and 2 are obtained, for l in very good agreement with the 31P single crystal NMR results. Only some of the orientational parameters of the three 13C chemical shielding tensors in the PEP moiety of 1 could be derived from 13C MAS NMR experiments with 31P rotary resonance recoupling.