Recombinant Human Homeobox protein Hox-D11 (HOXD11), is a member of the homeobox - containing family of proteins, play crucial roles in embryonic development.During embryonic development,HOXD11 is involved in the patterning of the body axis, especially in the regions related to limb development and axial skeleton formation. It acts as a transcriptional regulator. By binding to regulatory regions of target genes, it can either activate or repress their transcription. For example, in limb development, Hox - D11 helps determine the identity of cells along the proximal - distal axis of the limb bud. It ensures that the correct structures, such as the upper arm, forearm, and digits, develop in the appropriate positions. In the axial skeleton, it contributes to the proper differentiation of vertebrae and associated tissues.Besides,S100 Calcium Binding Protein A2 (S100A2) has been identified as an interactor of HOXD11, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human HOXD11 and recombinant human S100A2 . Briefly, biotin-linked HOXD11 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to S100A2-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µl stop solution to the wells and read at 450nm immediately. The binding activity of HOXD11 and S100A2 was shown in Figure 1, the EC50 for this effect is 0.16ug/mL.