title: Suppression of inhibin A biological activity by alterations in the binding site for betaglycan.
abstract: Inhibins A and B negatively regulate the production and secretion of follicle-stimulating hormone from the anterior pituitary, control ovarian follicle development and steroidogenesis, and act as tumor suppressors in the gonads. Inhibins regulate these reproductive events by forming high affinity complexes with betaglycan and activin or bone morphogenetic protein type II receptors. In this study, the binding site of inhibin A for betaglycan was characterized using inhibin A mutant proteins. An epitope for high affinity betaglycan binding was detected spanning the outer convex surface of the inhibin alpha-subunit. Homology modeling indicates that key alpha-subunit residues (Tyr(50), Val(108), Thr(111), Ser(112), Phe(118), Lys(119), and Tyr(120)) form a contiguous epitope in this region of the molecule. Disruption of betaglycan binding by the simultaneous substitution of Thr(111), Ser(112), and Tyr(120) to alanine yielded an inhibin A variant that was unable to suppress activin-induced follicle-stimulating hormone release by rat pituitary cells in culture. Together these results indicate that a high affinity interaction between betaglycan and residues Val(108)-Tyr(120) of the inhibin alpha-subunit mediate inhibin A biological activity.
authors.affiliation: Prince Henry's Institute of Medical Research, Clayton, Victoria 3168, Australia.
authors.forename: Yogeshwar
authors.initials: Y
authors.lastname: Makanji
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Walton
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Wilce
authors.forename: Karen L
authors.initials: KL
authors.lastname: Chan
authors.forename: David M
authors.initials: DM
authors.lastname: Robertson
authors.forename: Craig A
authors.initials: CA
authors.lastname: Harrison
mesh_terms: D028341:Activins / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D052006:Bone Morphogenetic Protein Receptors, Type II / Q000737:chemistry; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D007265:Inhibins / Q000037:antagonists & inhibitors*; D008969:Molecular Sequence Data; D011509:Proteoglycans / Q000737:chemistry*; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; C422362:inhibin A; D028341:Activins; C071736:betaglycan; D007265:Inhibins; D052006:Bone Morphogenetic Protein Receptors, Type II