POST, partner of stromal interaction molecule 1 (STIM1), targets STIM1 to multiple transporters.
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Krapivinsky G, Krapivinsky L, Stotz SC, Manasian Y, Clapham DE
POST, partner of stromal interaction molecule 1 (STIM1), targets STIM1 to multiple transporters.
Proc Natl Acad Sci U S A. 2011 Nov 29;108(48):19234-9. doi: 10.1073/pnas.1117231108. Epub 2011 Nov 14.
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- 22084111 [ View in PubMed]
- Abstract
Specialized proteins in the plasma membrane, endoplasmic reticulum (ER), and mitochondria tightly regulate intracellular calcium. A unique mechanism called store-operated calcium entry is activated when ER calcium is depleted, serving to restore intra-ER calcium levels. An ER calcium sensor, stromal interaction molecule 1 (STIM1), translocates within the ER membrane upon store depletion to the juxtaplasma membrane domain, where it interacts with intracellular domains of a highly calcium-selective plasma membrane ion channel, Orai1. STIM1 gates Orai1, allowing calcium to enter the cytoplasm, where it repletes the ER store via calcium-ATPases pumps. Here, we performed affinity purification of Orai1 from Jurkat cells to identify partner of STIM1 (POST), a 10-transmembrane-spanning segment protein of unknown function. The protein is located in the plasma membrane and ER. POST-Orai1 binding is store depletion-independent. On store depletion, the protein binds STIM1 and moves within the ER to localize near the cell membrane. This protein, TMEM20 (POST), does not affect store-operated calcium entry but does reduce plasma membrane Ca(2+) pump activity. Store depletion promotes STIM1-POST complex binding to smooth ER and plasma membrane Ca(2+) ATPases (SERCAs and PMCAs, respectively), Na/K-ATPase, as well as to the nuclear transporters, importins-beta and exportins.