ORAI1

Calcium release-activated calcium channel protein 1 is a calcium selective is_associated_with::ion channel that in humans is encoded by the ORAI1 is_associated_with::gene. Orai channels play an important role in the activation of is_associated_with::T-lymphocytes. The loss of function mutation of Orai1 causes is_associated_with::severe combined immunodeficiency (SCID) in humans The mammalian orai family has two additional homologs, orai2 and orai3. Orai proteins share no homology with any other ion channel family of any other known proteins. They have 4 is_associated_with::transmembrane domains and form tetramers.

Orai channels are activated upon the depletion of internal calcium stores, which is called the "store-operated" or the "capacitative" mechanism. They are molecular constituents of the "calcium release activated calcium currents" (is_associated_with::ICRAC). Upon activation of is_associated_with::phospholipase C by various cell surface receptors, is_associated_with::inositol trisphosphate is formed that releases calcium from the is_associated_with::endoplasmic reticulum. The decreased calcium concentration in the endoplasmic reticulum is sensed by the is_associated_with::STIM1 protein. STIM1 clusters upon the depletion of the calcium stores and forms "puncta", and relocates near the plasma membrane, where it activates orai1 via protein protein interaction.