Negative influence of O-linked oligosaccharides of high molecular weight equine chorionic gonadotropin on its luteinizing hormone and follicle-stimulating hormone receptor-binding activities.
Three equine CG (eCG) forms with identical amino acid sequences but different mol wt and monosaccharide compositions were isolated from a crude eCG preparation and designated eCG-L (low mol wt), eCG-M (medium mol wt), and eCG-H (high mol wt). No differences in primary structure between each form and the known sequence of eCG were observed. SDS-PAGE of these preparations under reducing conditions revealed that the mol wt differences between them were due only to the different sizes of their beta-subunits. Carbohydrate compositions suggested an increase in O-glycosylation in the higher mol wt forms. N-Linked glycopeptide fragments obtained from eCG beta-subunits by endoproteinase Lys-C digestion had identical electrophoretic mobilities. Thus, the different molecular sizes of the beta-subunits were associated only with disparities in O-glycosylation of their C-terminal extension. When tested in a LH and several FSH radioligand assay systems, eCG-H proved to have significantly lower receptor-binding activities than eCG-L and eCG-M. Endo-beta-galactosidase digestion increased the FSH receptor-binding activity of all eCG forms; however, partially deglycosylated eCG-H remained the least active form. Thus, the O-linked oligosaccharides of eCG-H exert a negative influence on its receptor-binding activity.
Butnev
V Y
VY
Department of Biological Sciences, Wichita State University, Kansas 67260, USA.
Gotschall
R R
RR
Baker
V L
VL
Moore
W T
WT
Bousfield
G R
GR
D000595:Amino Acid Sequence; D000818:Animals; D002236:Carbohydrate Conformation; D006063:Chorionic Gonadotropin / Q000737:chemistry* / Q000378:metabolism*; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006020:Glycopeptides / Q000737:chemistry / Q000378:metabolism; D006026:Glycoside Hydrolases; D006031:Glycosylation; D006736:Horses; D008297:Male; D008666:Metalloendopeptidases / Q000378:metabolism; D008970:Molecular Weight; D009005:Monosaccharides / Q000032:analysis; D009844:Oligosaccharides / Q000737:chemistry*; D051381:Rats; D011962:Receptors, FSH / Q000378:metabolism*; D011974:Receptors, LH / Q000378:metabolism*; D012756:Sheep; D013329:Structure-Activity Relationship; D001616:beta-Galactosidase / Q000378:metabolism
D006063:Chorionic Gonadotropin; D006020:Glycopeptides; D009005:Monosaccharides; D009844:Oligosaccharides; D011962:Receptors, FSH; D011974:Receptors, LH; D006026:Glycoside Hydrolases; C026093:keratan-sulfate endo-1,4-beta-galactosidase; D001616:beta-Galactosidase; D008666:Metalloendopeptidases; C039830:peptidyl-Lys metalloendopeptidase