Facilitation of Orai3 targeting and store-operated function by Orai1

Orai1 subunits interacting with STIM1 molecules comprise the major components responsible for calcium release-activated calcium (CRAC) channels. The homologs Orai2 and Orai3 yield smaller store-operated currents when overexpressed and are mostly unable to substitute Orail. Orai3 subunits are also essential components of store independent channel complexes and also tune inhibition of I-CRAC by reactive oxygen species. Here we use patch-clamp, microscopy, Ca2+-imaging and biochemical experiments to investigate the interdependence of Orai2, Orai3 and Orai1. We demonstrate that store-operation and localization of Orai3 but not of Orai2 to STIM1 clusters in HEK cells or to the immunological synapse in T cells is facilitated by Orail while Orai3's store-independent activity remains unaffected. On the other hand, one Orai3 subunit confers redox-resistance to heteromeric channels. The inefficient store operation of Orai3 is partly due to the lack of three critical C-terminal residues, the insertion of which improves interaction with STIM1 and abrogates Orai3's dependence on Orail. Our results suggest that Orai3 down-tunes efficient STIM1 gating when in a heteromeric complex with Orail. (C) 2015 Elsevier B.V. All rights reserved.