Identification of twelve O-glycosylation sites in equine chorionic gonadotropin beta and equine luteinizing hormone beta by solid-phase Edman degradation

The O-glycosylation sites for equine LH beta (eLH beta) and eCG beta were i dentified by solid-phase Edman degradation of four glycopeptides derived fr om the C-terminal region. Both subunits were O-glycosylated at the same 12 positions, rather than the 4-6 sites anticipated, These sites were partiall y glycosylated, with carbohydrate attachment ranging from 20% to 100% for e CG beta and from 10% to 100% for eLH beta. When the C-terminal peptide cont aining all but one of the O-linked oligosaccharides was removed by mild aci d hydrolysis of either eLH beta or eCG beta, hybrid hormones could be obtai ned by reassociating eLH alpha, eFSH alpha, or eCG alpha with the truncated beta subunit derivatives. These hybrid hormones were identical in LH recep tor-binding activity when des(121-149)eLH beta or des(121-149)eCG beta were combined with the same alpha subunit preparation, Thus, O-glycosylation ap pears to be responsible for the beta subunit contribution to the substantia l difference in LH receptor-binding activity between eLH and eCG, Compariso n of the equid LH/CG beta sequences with those available for the primate CG beta subunits indicated a greater conservation of glycosylation patterns i n the former.