Mechanism Of Interaction Between Orai And STIM1

Calcium plays a crucial role in many cellular processes, such as gene transcription, cell proliferation, differentiation and apoptosis etc, and also the intracellular calcium concentration change is closely related to the signal transduction and many diseases, so the intracellular calcium homeostasis, which is regulated by the calcium channel on the plasma membrane, calcium pump and calcium store is essential for physiological function. In non-excitable cells, store-operated calcium entry (SOCE) is the main machinery for calcium entry, and also is critical for T cell activation. The activation of SOCE requires engagement between stromal interaction molecule1(STIM1) molecules on the endoplasmic reticulum and Ca2+release-activated Ca2+(CRAC) channels Orail on the plasma membrane. The recent structural resolution of both proteins has substantially advanced the understanding of the activation mechanism of CRAC channels; the SOAR domain of STIM1coupling both Orail C and N terminus and activation of Orail channels. However, the molecular details of their interactions remain elusive. Here, we analyzed the STIM1-Orai interactions using synthetic peptides derived from NT (N terminus) and CT (C terminus) of Orai and purified fragments of STIM1, and identified important regions in the NT and CT of Orai, The binding of STIM1to Orai-NT is hydrophilic-based, whereas that to the CT is mostly hydrophobic. STIM1reduces its affinity for CT peptides when the NT ones is present, confirming a directional stepwise interaction. Orai3-CT exhibit stronger binding to STIM1than that of Orail, largely due to a lack of one helical turn. Finally, the administration of an Orai3-CT peptide effectively inhibited CRAC channel activity. Our results not only provide significant insight into CRAC channel gating by STIM1, but also implicate a therapeutic potential of membrane permeable peptides developed in this study as immunosuppressants for selective CRAC channel inhibition.