title: Characterization of the ligand binding functionality of the extracellular domain of activin receptor type IIb.
abstract: The single transmembrane domain serine/threonine kinase activin receptor type IIB (ActRIIB) has been proposed to bind key regulators of skeletal muscle mass development, including the ligands GDF-8 (myostatin) and GDF-11 (BMP-11). Here we provide a detailed kinetic characterization of ActRIIB binding to several low and high affinity ligands using a soluble activin receptor type IIB-Fc chimera (ActRIIB.Fc). We show that both GDF-8 and GDF-11 bind the extracellular domain of ActRIIB with affinities comparable with those of activin A, a known high affinity ActRIIB ligand, whereas BMP-2 and BMP-7 affinities for ActRIIB are at least 100-fold lower. Using site-directed mutagenesis, we demonstrate that ActRIIB binds GDF-11 and activin A in different ways such as, for example, substitutions in ActRIIB Leu(79) effectively abolish ActRIIB binding to activin A yet not to GDF-11. Native ActRIIB has four isoforms that differ in the length of the C-terminal portion of their extracellular domains. We demonstrate that the C terminus of the ActRIIB extracellular domain is crucial for maintaining biological activity of the ActRIIB.Fc receptor chimera. In addition, we show that glycosylation of ActRIIB is not required for binding to activin A or GDF-11. Together, our findings reveal binding specificity and activity determinants of the ActRIIB receptor that combine to effect specificity in the activation of distinct signaling pathways.
authors.affiliation: Acceleron Pharma, Cambridge, MA 02139, USA.
authors.forename: Dianne
authors.initials: D
authors.lastname: Sako
authors.forename: Asya V
authors.initials: AV
authors.lastname: Grinberg
authors.forename: June
authors.initials: J
authors.lastname: Liu
authors.forename: Monique V
authors.initials: MV
authors.lastname: Davies
authors.forename: Roselyne
authors.initials: R
authors.lastname: Castonguay
authors.forename: Silas
authors.initials: S
authors.lastname: Maniatis
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Andreucci
authors.forename: Eileen G
authors.initials: EG
authors.lastname: Pobre
authors.forename: Kathleen N
authors.initials: KN
authors.lastname: Tomkinson
authors.forename: Travis E
authors.initials: TE
authors.lastname: Monnell
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Ucran
authors.forename: Erik
authors.initials: E
authors.lastname: Martinez-Hackert
authors.forename: R Scott
authors.initials: RS
authors.lastname: Pearsall
authors.forename: Kathryn W
authors.initials: KW
authors.lastname: Underwood
authors.forename: Jasbir
authors.initials: J
authors.lastname: Seehra
authors.forename: Ravindra
authors.initials: R
authors.lastname: Kumar
mesh_terms: D030301:Activin Receptors, Type II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D018076:DNA, Complementary / Q000235:genetics; D017930:Genes, Reporter; D006801:Humans; D008024:Ligands; D016296:Mutagenesis; D050506:Mutant Chimeric Proteins / Q000737:chemistry / Q000378:metabolism; D055435:Myostatin / Q000737:chemistry / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D010960:Plasminogen Activators / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D008024:Ligands; D050506:Mutant Chimeric Proteins; D055435:Myostatin; D011993:Recombinant Fusion Proteins; D030301:Activin Receptors, Type II; C425584:activin receptor type II-B; D010960:Plasminogen Activators
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