Heat Shock 70kDa Protein 9 (HSPA9), also termed mortalin, belongs to the conserved Hsp70 chaperone family and predominantly localizes in mitochondria. It mediates mitochondrial protein import, facilitates proper folding of newly synthesized polypeptides, and eliminates misfolded or aggregated proteins to maintain mitochondrial proteostasis. Beyond chaperone functions, HSPA9 participates in regulating cellular metabolism, oxidative stress response, cell proliferation and apoptosis. Dysregulated HSPA9 expression is closely linked to tumour progression, neurodegenerative disorders and mitochondrial dysfunction-related diseases. It stabilizes mitochondrial membrane integrity and balances reactive oxygen species levels, acting as a vital guardian of mitochondrial homeostasis under physiological and stress conditions. HSPA9 directly interacts with ITPR1 to modulate endoplasmic reticulum-mitochondria calcium transfer. Thus a functional ELISA assay was conducted to detect the interaction of recombinant human HSPA9 and recombinant human ITPR1. Briefly, HSPA9 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-HSPA9 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 HSPA9 and recombinant human ITPR1 was shown in Figure 1, the EC50?for this effect is 1.06326μg/mL.