Identification of a binding site on the type II activin receptor for activin and inhibin.
Type II activin receptors (ActRII and ActRIIB) are single-transmembrane domain serine/threonine kinase receptors that bind activin to initiate the signaling and cellular responses triggered by this hormone. Inhibin also binds type II activin receptors and antagonizes many activin effects. Here we describe alanine scanning mutagenesis of the ActRII extracellular domain. We identify a cluster of three hydrophobic residues (Phe(42), Trp(60), and Phe(83)) that, when individually mutated to alanine in the context of the full-length receptor, cause the disruption of activin and inhibin binding to ActRII. Each of the alanine-substituted ActRII mutants retaining activin binding maintains the ability to form cross-linked complexes with activin and supports activin cross-linking to the type I activin receptor ALK4. Unlike wild-type ActRII, the three mutants unable to bind activin do not cause an increase in activin signaling when transiently expressed in a corticotroph cell line. Together, our results implicate these residues in forming a critical binding surface on ActRII required for functional interactions with both activin and inhibin. This first identification of a transforming growth factor-beta family member binding site may provide a general basis for characterizing binding sites for other members of the superfamily.
Gray
P C
PC
Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, California 92037, USA.
Greenwald
J
J
Blount
A L
AL
Kunitake
K S
KS
Donaldson
C J
CJ
Choe
S
S
Vale
W
W
D029404:Activin Receptors; D028341:Activins; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D007265:Inhibins / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism; D017978:Receptors, Growth Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
D017978:Receptors, Growth Factor; D028341:Activins; D007265:Inhibins; D017346:Protein Serine-Threonine Kinases; D029404:Activin Receptors