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Differences in the carbohydrate moieties of the common alpha subunits of human chorionic gonadotropin luteinizing hormone fsh and thyrotropin preliminary structural inferences from direct methylation analysis


Endocrinology 119(6): 2737-2743
Differences in the carbohydrate moieties of the common alpha subunits of human chorionic gonadotropin luteinizing hormone fsh 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''-O-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.


Accession: 005151132



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