Figure 9.

STIM2 facilitates STIM1-Orai1 interaction. (A) Immunoprecipitation studies using NIH 3T3 cell extracts under store-filled (Control) or store-depleted (CPA) conditions. Immunoprecipitation was performed using anti-STIM1 antibody followed by immunoblotting with anti-STIM2 and anti-Orai1 antibodies. The STIM1 antibody pulled down STIM2 and Orai1 under both conditions; however, the interaction was enhanced in store-depleted conditions. The input protein (Pre-IP) and the protein remaining after pull-down (Post-IP) are shown. Molecular mass markers are indicated. (B) Changes in FRET between YFP-STIM1 and CFP-Orai1 as intracellular Ca²⁺ stores were depleted (open bar; 0Ca²⁺/CPA) and then refilled (open bar; +Ca²⁺) in WT (black line) and STIM2 KO2-1 (red line). The data are expressed as the mean ± SEM fold-change in FRET FI535/FI485 relative to FI535/FI485 in resting unstimulated cells from five independent experiments (WT: n = 28 cells; KO2-1: n = 26 cells). FI535/FI485 in resting unstimulated cells was not different in KO2-1 compared to control. (C) The maximum values of fold-change in FRET FI535/FI485 (Max FRET). * p < 0.05 compared to WT.