Differences in the carbohydrate moieties of the common alpha-subunits of human chorionic gonadotropin, luteinizing hormone, follicle-stimulating hormone, and thyrotropin: preliminary structural inferences from direct methylation analysis.

The carbohydrate components of combined alpha-subunits of urinary hCG and human pituitary LH (hLH), FSH (hFSH), and TSH (hTSH), each derived from the intact hormone, were studied by direct sugar analysis and methylation analysis. The methods provide a complete survey of the structural elements contained in the complex sugars associated with these glycoproteins, but do not establish the sugar sequences or anomeric configurations of glycosidic bonds. By analogy to N-linked oligosaccharides that occur in many glycoproteins, the data suggest distinct structural features for carbohydrates of alpha-subunits combined with beta-subunits. hCG alpha contains biantennary asparagine-linked chains terminated by either NeuAc alpha 2-3Gal beta 1- or GlcNAc beta 1-2 Man alpha 1- and lacks fucose. hTSH alpha contains biantennary chains with the same termini as hCG alpha plus terminal R-O-4GalNAc and a fucosyl residue linked alpha 1-6 to the inner GlcNAc residue of the N-linked chitobiosyl core. hLH alpha may contain some high mannose chains, but primarily contains biantennary chains terminated by NeuAc alpha 2-3(6)Gal beta 1-, GlcNAc beta 1-, GalNac-1-, R'-O-6GlcNAc-1-, and R"-0-2Man-1-plus a fucosyl residue linked alpha 1-6 to the inner GlcNAc residue of the N-linked chitobiosyl core. hFSH alpha contains more complicated structures that probably include a bisecting GlcNAc residue linked beta 1-4 to a 3,6-di-O-substituted core mannosyl residue, and terminal NeuAc alpha 2-3Gal beta 1-4(+/- Fuc alpha 1-3)GlcNAc-1, Gal beta 1-4(+/- Fuc alpha 1-3)GlcNAc-1-, R"'-O-GalNAc-1-, and GalNAc-1. In addition, the presence of 2,4-di-O-substituted mannose in hFSH alpha indicates that it contains triantennary chains. The identities of the R; R', R", and R"' groups were not determined, but recent studies of glycoprotein hormones suggest that they may be sulfate groups. Our results demonstrate differential glycosylation of virtually identical polypeptide hormone alpha-subunits produced in the same organ or perhaps even in the same cell.