Molybdate-Stabilized Glucocorticoid Receptor: Evidence for a Receptor Heteromer

The composition of the molybdate-stabilized glucocorticoid receptor (GR) complex has been investigated with a monoclonal antibody against the steroid-binding M_r 94000 (94K) GR protein. It was concluded that one antibody molecule binds one 94K GR molecule. This finding constituted the basis for calculating the number of antibodies bound to the molybdate-stabilized nonactivated GR complex, which has an M_r of 302000 (302K). Gel filtration on Sephacryl S-400 and density gradient centrifugation showed that only one antibody molecule bound to the molybdate-stabilized GR complex (calculated relative molecular mass for the antibody-molybdate-stabilized GR complex, 456000; relative molecular mass for one antibody molecule, 157000). Furthermore, experiments performed with a second antibody immunoprecipitation assay in the presence of an excess of both antibody and GR confirmed the above results. The possibility of steric hindrance not allowing more than one antibody molecule to bind to the molybdate-stabilized GR complex could be excluded. These results suggest that the molybdate-stabilized GR complex with an M_r. of 302K only contains one steroid-binding 94K GR molecule and therefore represents a heteromeric complex.