The Orai family of
calcium channels includes the store-operated
CRAC channels and store-independent,
arachidonic acid (AA)-regulated
ARC channels. Both depend on STIM1 for their activation but, whereas
CRAC channel activation involves sensing the depletion of intracellular
calcium stores via a
luminal N terminal EF-hand of STIM1 in the endoplasmic reticulum (ER) membrane,
ARC channels are exclusively activated by the pool of STIM1 that constitutively resides in the plasma membrane (PM). Here, the EF-hand is extracellular and unlikely to ever lose its bound
calcium, suggesting that STIM1-dependent activation of
ARC channels is very different from that of
CRAC channels. We now show that attachment of the cytosolic portion of STIM1 to the inner face of the PM via an N terminal Lck-domain sequence is sufficient to enable normal AA-dependent activation of
ARC channels, while failing to allow activation of store-operated
CRAC channels. Introduction of a point mutation within the Lck-domain resulted in the loss of both PM localization and
ARC channel activation. Reversing the orientation of the PM-anchored STIM1 C terminus via a C-terminal CAAX-box fails to support either CRAC or
ARC channel activation. Finally, the Lck-anchored STIM1 C-terminal domain also enabled the exclusive activation of the
ARC channels following physiological agonist addition. These data demonstrate that simple tethering of the cytosolic C-terminal domain of STIM1 to the inner face of the PM is sufficient to allow the full, normal and exclusive activation of
ARC channels, and that the N-terminal regions of STIM1 (including the EF-hand domain) play no significant role in this activation.