Purification and identification of an estrogen binding protein from rat brain: oligomycin sensitivity-conferring protein (OSCP) a subunit of mitochondrial F0F1-ATP synthase/ATPase

Early studies have suggested the presence in the central nervous system of possible estrogen binding sites/proteins other than classical nuclear estrogen receptors (nER). We report here the isolation and identification of a 23 kDa membrane protein from digitonin-solubilized rat brain mitochondrial fractions that binds 17 beta-estradiol conjugated to bovine serum albumin at C-6 position (17 beta-E-6-BSA), a ligand that also specifically binds nER. This protein was partially purified using affinity columns coupled with 17 beta-E-6-BSA and was recognized by the iodinated 17 beta-E-6-BSA (17 beta-E-6-[I-125]BSA) in a ligand blotting assay.. The binding of 17 beta-E-6-BSA to this protein was specific for the 17 beta-estradiol portion of the conjugate, not BSA. Using N-terminal sequencing and immunoblotting, this 23 kDa protein was identified as the oligomycin-sensitivity conferring protein (OSCP). This protein is a subunit of the F0F1 (F-type) mitochondrial ATP synthase/ATPase required for the coupling of a proton gradient across the F0 sector of the enzyme in the mitochondrial membrane to ATP synthesis in the Fl sector of the enzyme. Studies using recombinant bovine OSCP (rbOSCP) in ligand blotting revealed that rbOSCP bound 17 beta-E-6-[I-125]BSA with the same specificity as the purified 23 kDa protein. Further, in a ligand binding assay, 17 beta-E-6-[I-125]BSA also bound rbOSCP and it was displaced by both 17 beta-E-6-BSA and 17 alpha-E-6-BSA as well as partially by 17 beta-estradiol and diethylstilbestrol (DES), but not by BSA. This finding opens up the possibility that estradiol, and probably other compounds with similar structures, in addition to their classical genomic mechanism, may interact with ATP synthase/ATPase by binding to OSCP: and thereby modulating cellular energy metabolism. Current experiments are addressing such an issue. (C) 1999 Elsevier Science Ltd. All rights reserved.