Stress Induced Phosphoprotein 1 (STIP1), also known as Hsp70/Hsp90 organizing protein (HOP), is a versatile co-chaperone that bridges Hsp70 and Hsp90 to facilitate proper folding and maturation of client proteins. It plays pivotal roles in stress response, neuronal function, and cancer progression by regulating protein quality control systems. STIP1 is overexpressed in various malignancies and participates in extracellular signaling via interactions with prion proteins. STIP1 binds to the cellular Prion Protein (PRNP) through direct physical interaction, modulating PRNP's neuroprotective functions and potentially influencing prion disease pathogenesis.Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human STIP1 and recombinant human PRNP. Briefly, STIP1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to PRNP-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-STIP1 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 STIP1 and recombinant human PRNP was shown in Figure 1, the EC50 for this effect is 0.79µg/mL.