The expression of milligram amounts of functional human 1,25-dihydroxyvitamin D₃ receptor in a bacterial expression system

We expressed milligram amounts of functional human 1,25-dihydroxyvitamin D₃ receptor in a bacterial expression system in which the cloned cDNA for the hVDR was expressed under the control of bacterial T₇ polymerase. The hVDR protein comprised approximately 60% of total bacterial protein. It migrated on polyacrylamide-sodium dodecyl sulfate gels with an M_r of 48,000. It had the predicted amino acid composition and amino acid sequence analysis. The expressed protein was bound by 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) with a Kd in the nanomolar range. It sedimented on sucrose density gradients at 3.5S. Furthermore, the expressed protein bound to the osteocalcin vitamin D response element (VDRE) as assessed by a gel mobility shift assay. The expression of large amounts of hVDR protein should allow for the use of this protein in structure-function and x-ray crystallography studies.