Recombinant Human CDO Protein, CF

CDO (CAM-related/down-regulated by oncogenes, also CDON; pronounced “kid-oh”) is a 190 kDa member of the Immunoglubulin (Ig) superfamily, Ig/Fibronectin (FN) type III repeat family of cell surface proteins (1). Human CDO is a type I transmembrane (TM) glycoprotein. It is synthesized as a 1287 amino acid (aa) precursor that contains a 25 aa signal sequence, a 938 aa extracellular domain (ECD), a 21 aa TM segment and a 303 aa cytoplasmic region (1, 2). The ECD contains five C2-type Ig-like domains, followed by three FN type III repeats. The first FN repeat (aa 577 - 673) is known to bind numerous cadherins, while the third (or juxtramembrane) FN type III repeat (aa 826 - 923) binds SHH (3, 4). The intracellular region is believed to signal through various bHLH transcription factors (2). One alternate splice form is reported that shows a deletion of aa 1212 - 1234 in the cytoplasmic tail. The ECD of human CDO is 85% aa identical to mouse CDO ECD. CDO is found on muscle precursor and neural progenitor cells of the embryo (5, 6). It likely promotes muscle differentiation, and contributes to axon guidance and neuronal patterning (2, 7, 8, 9). These effects may be mediated through two different receptor complexes. On muscle precursors, CDO apparently acts as both a coordinating and signaling subunit. Here, it integrates N- and M-cadherin, neogenin, netrin-3 and BOC into a cis-oriented receptor complex (2). While this complex has no identified ligand, intercellular cadherin interactions or netrin, may be enough to trigger CDO/cadherin/neogenin signaling. On axons, CDO may participate in a poorly-defined receptor complex minimally composed of CDO, BOC and Gas1 that binds SHH, and interacts with PTCH1 (7, 8, 10).