Stromal Interaction Molecule 1 (STIM1) is a single-pass transmembrane protein located primarily in the endoplasmic reticulum (ER) membrane. It functions as a critical calcium sensor in the process of store-operated calcium entry (SOCE). When ER calcium stores are depleted, STIM1 undergoes conformational changes, oligomerizes, and translocates to ER-plasma membrane junctions where it interacts with and activates Orai channels, facilitating extracellular Ca²⁺ influx. This process is essential for various cellular functions including immune response, muscle contraction, and gene expression. STIM1 directly binds to the Inositol-1,4,5-Trisphosphate Receptor Type 1 (ITPR1), an ER-resident calcium release channel, to regulate its stability and calcium release activity.
To detect the activity of recombinant STIM1 , a functional ELISA assay was performed to evaluate the interaction between recombinant human STIM1 and recombinant human ITPR1.Briefly, STIM1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ITPR1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-STIM1 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant human STIM1 and recombinant human ITPR1 was shown in Figure 1, the EC50 for this effect is 0.08 µg/mL.