Structural requirements for sulfation of asparagine-linked oligosaccharides of lutropin.

Human and bovine pituitary glycoprotein hormones (lutropin, follitropin, and thyrotropin) contain varying amounts of N-acetylgalactosamine and sulfate. The sulfate on asparagine-linked oligosaccharides of bovine lutropin (bLH) is present exclusively on GalNAc in the sequence GalNAc(beta 1-4)GlcNAc(beta 1-2)Man alpha. We have examined the structural requirements for sulfation of bLH oligosaccharides by using a reconstituted cell-free system. After cleavage from the protein, oligosaccharides containing the sequence GalNAc(beta 1-4)Glc-NAc(beta 1-2)Man alpha were sulfated by enzymes in pituitary membranes. Addition of one or two sulfates was observed, depending upon the number of GalNAc acceptor sites on the oligosaccharide. Neither GalNAc alone nor oligosaccharides devoid of GalNAc were sulfated. Membranes from placenta or liver did not sulfate oligosaccharides released from bLH, indicating that the sulfating activity is pituitary-specific. The lack of peptide dependence for sulfation, in conjunction with the oligosaccharide specificity, suggests that the sequence GalNAc(beta 1-4)GlcNAc(beta 1-2)Man alpha contains the recognition signal for the sulfotransferase(s).