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 identical peptide maps and are both recognized by anti-estrogen receptor (R-I) IgG. Both are tyrosine kinases and bind with equal affinity to a column of anti-phosphotyrosine IgG-Sepharose. On the other hand, while naER is a glycoprotein, the R-II does not show any sign of glycosylation. Unlike the naER, the R-II is incapable of dimerization with estrogen receptor activation factor (E-RAF) and, as a consequence, bind to the DNA. R-II has a higher estradiol binding capacity and the resultant 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 corresponding data for the R-II reveal that the protein has a distinct nonglobular shape. Deglycosylation of the naER using a glycopeptidase resulted 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 dimerization capacity of the naER. The Stokes radius and the sedimentation coefficient of the protein underwent drastic changes and became closely similar to those of the R-II. In addition, the deglycosylation introduced a several-fold enhancement in the capacity of the naER to bind estradiol with a concomitant decrease in its affinity, similar to the corresponding properties of the R-II. The R-II is shown to have a conformational structure different from that of the naER, to interact with the nuclear RNA polymerase II. It is also shown here that the R-II phosphorylates two subunits (molecular mass 91 and 20 kDa) in the RNA polymerase II, in addition to the 40-kDa subunit phosphorylated by the naER. The results clearly indicate the possibility that the nuclear R-II estrogen receptor is the deglycosylated naER.