Purification and characterization of an estrogen-inducible membrane glycoprotein. Evidence that it is a transferrin receptor.

Abstract

A number of N-linked membrane glycoproteins are induced during chick oviduct differentiation. We have purified a major estrogen-inducible glycoprotein (Mr = 91,000) to homogeneity by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Comparison of partial NH2-terminal sequence data with membrane glycoproteins having similar Mr showed a limited homology with human and murine transferrin receptors. We observed that oviduct membranes contain estrogen-inducible transferrin receptor activity (Kd = 2-8 x 10(-8) M). Analytical purification of the putative receptor on an ovotransferrin-Affi-Gel affinity column and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis reveals a protein of Mr, 180,000, which contains two disulfide-linked subunits of Mr 91,000. The receptor reacts very strongly with antibodies prepared against the 91-kDa glycoprotein on Western blots. Western blot analysis confirms that the 91-kDa glycoprotein is induced by estrogen. The protein has 2% total carbohydrate with Man, GlcNAc, Gal, GalNAc, and NeuAc in a molar ratio of 6:4:2:1:1. The protein contains at least one O-linked moiety. Analysis of the O-linked moiety by glycosidase digestions and gel filtration indicates there are sialo tetra- and trisaccharides and a neutral disaccharide(s). Labeled N-linked glycopeptides were prepared by pronase digestion, beta-elimination, and 3H-acetylation. The N-linked oligosaccharides include high mannose and complex neutral nonbisected biantennary types in an approximate ratio of 3:1 as determined by serial lectin affinity chromatography.