This domain contains 9 conserved cysteines and is extracellular. Therefore the cysteines may form disulphide bridges. This family of proteins has been termed the DAN family after the first member to be reported. This family includes DAN, Cerberus and Gremlin. The gremlin protein is an antagonist of bone morphogenetic protein signaling. It is postulated that all members of this family antagonize different TGF beta pfam00019 ligands. Recent work shows that the DAN protein is not an efficient antagonist of BMP-2/4 class signals, we found that DAN was able to interact with GDF-5 in a frog embryo assay, suggesting that DAN may regulate signaling by the GDF-5/6/7 class of BMPs in vivo.