Structural relationship, biosynthesis, and immunocytochemical localization of uteroferrin-associated basic...

Uteroferrin, a progesterone-induced secretory protein of the pig uterus, can noncovalently associate with additional progesterone-induced glycoproteins (uteroferrin-associated glycoproteins or UfAP) to form a heterodimer. The UfAP were dissociated from uteroferrin by passage through an immunoaffinity column. The flow through material consisted of two immunologically related variants of different size (Mr = 47,000-50,000 and Mr = 39,000-40,000) forms. By using an antiserum to all molecular weight components of the UfAP, it was shown that these glycoproteins were localized in the glandular epithelium of the uterus. Amino acid sequence analysis of the higher molecular weight (Mr = 47,000-50,000) form indicated it had a common amino-terminal sequence which was distinct from that of the lower molecular weight (Mr = 39,000-40,000) form. Endoglycosidase F treatment converted the Mr = 47,000-50,000 form to a common product with Mr = 43,000. Tryptic peptide analysis showed that the Mr = 39,000-40,000 form was closely related in primary sequence to the larger species. When endometrial RNA was translated in vitro, a single major product (Mr = 45,000) was immunoprecipitated by using the UfAP antiserum. These results suggest that the different forms of the UfAP originate from a single precursor by differential glycosylation and peptide cleavage. Endometrial explant cultures released all forms of the glycoproteins. When [32P]orthophosphate was provided, label was incorporated into the 6-position of D-mannosyl residues on the oligosaccharide chains of the UfAP. Therefore the associated glycoproteins have a structural feature normally associated with lysosomal enzymes.