Glypican 5 (GPC5) belongs to the glypican family of proteoglycans that are linked to the cell surface through a glycosyl-phosphatidylinositol anchor. GPC5 is expressed primarily in embryonic neurons and mesenchyme and it is implicated in a variety of physiological processes, ranging from cell proliferation to morphogenesis. Besides, Syndecan 1 (SDC1) has been identified as an interactor of GPC5, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant rat GPC5 and recombinant human SDC1. Briefly, GPC5 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to SDC1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-GPC5 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 450/630 nm immediately. The binding activity of recombinant rat GPC5 and recombinant human SDC1 was shown in Figure 1, the EC50 for this effect is 0.6 ug/mL.