THE NUCLEAR ESTROGEN-RECEPTOR R-II OF THE GOAT UTERUS - DISTINCT POSSIBILITY THAT THE R-II IS THE DEGLYCOSYLATED FORM OF THE NONACTIVATED ESTROGEN-RECEPTOR (NAER)

Structural and functional characteristics of the goat uterine nuclear estrogen receptor R-II have been subjected to comparison with those of the nonactivated estrogen receptor (naER), purified from the cytosol. The two proteins have the same molecular mass, 66 kDa; they display i dentical peptide maps and are both recognized by anti-estrogen recepto r (R-I) IgG. Both are tyrosine kinases and bind with equal affinity to a column of anti-phosphotyrosine IgG-Sepharose. On the other hand, wh ile naER is a glycoprotein, the R-II does not show any sign of glycosy lation. Unlike the naER, the R-II is incapable of dimerization with es trogen receptor activation factor (E-RAF) and, as a consequence, bind to the DNA. R-II has a higher estradiol binding capacity and the resul tant reduction in its affinity for the hormone in comparison with the naER, Further, the sedimentation behavior and the Stokes radius of the naER indicate a globular nature in the shape of the protein, The corr esponding data for the R-II reveal that the protein has a distinct non globular shape. Deglycosylation of the naER using a glycopeptidase res ulted in the total conversion of the distinct physical features of the naER to the R-II category. This treatment resulted, without effecting any reduction in its molecular mass, in the loss of the E-RAF dimeriz ation capacity of the naER. The Stokes radius and the sedimentation co efficient of the protein underwent drastic changes and became closely similar to those of the R-II. In addition, the deglycosylation introdu ced a several-fold enhancement in the capacity of the naER to bind est radiol with a concomitant decrease in its affinity, similar to the cor responding properties of the R-II, The R-II is shown to have a conform ational structure different from that of the naER, to interact with th e nuclear RNA polymerase II. It is also shown here that the R-II phosp horylates two subunits (molecular mass 91 and 20 kDa) in the RNA polym erase II, in addition to the 40-kDa subunit phosphorylated by the naER . The results clearly indicate the possibility that the nuclear R-II e strogen receptor is the deglycosylated naER. (C) 1995 Academic Press, Inc.