Immunoaffinity Purification of Active Rat Recombinant 1,25-Dihydroxyvitamin D3 Receptor

We have developed a large-scale immunoaffinity purification procedure for the recombinant vitamin D receptor. The purified receptor is homogenous, and is bound by 1,25-dihydroxyvitamin D3 with a Kd of 5 × 10−10 M. The isolated receptor binds to the osteocalcin vitamin D response element in the presence of porcine intestinal nuclear extract stripped of endogenous vitamin D receptor as well. However, the binding of D3 and the vitamin D3 response element does not completely assure a native conformation of the protein. The availability of large quantities of highly purified active vitamin D receptor makes possible detailed structural analysis.