PMID: 1991473

 

    Legend: Sugar

Title : NMR investigations of the N-linked oligosaccharides at individual glycosylation sites of human lutropin

Abstract :

1. Human lutropin or luteinizing hormone ( hLH ) is a heterodimeric glycoprotein , composed of two subunits
2. hLH alpha (N-glycosylated at Asn52 and Asn78 ) and hLH beta (N-glycosylated at Asn30 )
3. The sugar chains were liberated by hydrazinolysis from intact hLH beta and from glycopeptides obtained after tryptic digestion of hLH alpha , subsequently reduced and fractionated as alditols by anion-exchange and ion-suppression amine-adsorption HPLC and identified mainly by one-dimensional (1D) and two-dimensional (2D) 1H-NMR spectroscopy
4. The results indicate predominantly diantennary
5. N-acetyllactosamine-type structures at all three glycosylation sites.
6. The oligosaccharides attached to Asn52 ( hLH alpha ) and Asn30 ( hLH beta ) show a remarkably similar pattern, with mainly chain-terminating 4-sulphated 2-deoxy-2-N-acetylamino-D-galactose (GalNAc) and a sulphated/sialylated structure as the major single component
7. However, virtually all N-glycans on the beta subunit bear a fucose residue alpha 1-6-linked to the proximal GlcNAc, whereas those at Asn52 (and Asn78 ) of the alpha subunit are predominantly non-fucosylated
8. The oligosaccharides at Asn78 ( hLH alpha ) are sialylated rather than sulphated and contain the unique sequence NeuAc alpha 2-6 GalNAc beta 1-4GlcNAc beta 1-2 Man alpha 1-3 as part of the majority of mono- and disialylated compounds
9. The major single constituent at Asn78 has the following structure: [formula, see text