title: A common biosynthetic pathway governs the dimerization and secretion of inhibin and related transforming growth factor beta (TGFbeta) ligands.
abstract: The assembly and secretion of transforming growth factor beta superfamily ligands is dependent upon non-covalent interactions between their pro- and mature domains. Despite the importance of this interaction, little is known regarding the underlying regulatory mechanisms. In this study, the binding interface between the pro- and mature domains of the inhibin alpha-subunit was characterized using in vitro mutagenesis. Three hydrophobic residues near the N terminus of the prodomain (Leu(30), Phe(37), Leu(41)) were identified that, when mutated to alanine, disrupted heterodimer assembly and secretion. It is postulated that these residues mediate dimerization by interacting non-covalently with hydrophobic residues (Phe(271), Ile(280), Pro(283), Leu(338), and Val(340)) on the outer convex surface of the mature alpha-subunit. Homology modeling indicated that these mature residues are located at the interface between two beta-sheets of the alpha-subunit and that their side chains form a hydrophobic packing core. Mutation of these residues likely disturbs the conformation of this region, thereby disrupting non-covalent interactions with the prodomain. A similar hydrophobic interface was identified spanning the pro- and mature domains of the inhibin beta(A)-subunit. Mutation of key residues, including Ile(62), Leu(66), Phe(329), and Pro(341), across this interface was disruptive for the production of both inhibin A and activin A. In addition, mutation of Ile(62) and Leu(66) in the beta(A)-propeptide reduced its ability to bind, or inhibit the activity of, activin A. Conservation of the identified hydrophobic motifs in the pro- and mature domains of other transforming growth factor beta superfamily ligands suggests that we have identified a common biosynthetic pathway governing dimer assembly.
authors.affiliation: Prince Henry's Institute of Medical Research, 246 Clayton Road, Clayton, Victoria 3168, Australia.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Walton
authors.forename: Yogeshwar
authors.initials: Y
authors.lastname: Makanji
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: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007265:Inhibins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D016212:Transforming Growth Factor beta / Q000145:classification / Q000378:metabolism*
chemical_list: D008024:Ligands; D021122:Protein Subunits; D016212:Transforming Growth Factor beta; D007265:Inhibins