Bacterial synthesis of truncated forms of the human vitamin D receptor and characterization of anti-receptor monoclonal antibodies.

We biosynthesized full-length (amino acids 1-427) and truncated human 1,25-dihydroxyvitamin D3 receptor proteins that encompassed only the putative DNA binding domain (amino acids 1-112) or the DNA binding domain and parts of the sterol binding domain (amino acids 1-193 and 1-328) in a bacterial expression system. We also prepared monoclonal antibodies against the full-length vitamin D receptor. The binding properties of the monoclonal antibodies were characterized by their ability to bind to full-length and truncated vitamin D receptor protein constructs. Seven of twelve monoclonal antibodies recognized the full-length receptor protein. These antibodies bound to truncated hVDR proteins with decreasing affinities as successive truncations were made from the carboxy-terminal end of the receptor protein. The five remaining monoclonal antibodies recognized the full-length and truncated receptor proteins with equally low affinities. Truncated forms of the vitamin D receptor and region-specific antibodies will be useful in assessing the properties of the receptor.