ACVR1B

Activin receptor type-1B is a is_associated_with::protein that in humans is encoded by the ACVR1B is_associated_with::gene.

ACVR1B or ALK-4 acts as a transducer of activin or activin like ligands (e.g., inhibin) signals. Activin binds to either is_associated_with::ACVR2A or is_associated_with::ACVR2B and then forms a complex with ACVR1B. These go on to recruit the is_associated_with::R-SMADs is_associated_with::SMAD2 or is_associated_with::SMAD3. ACVR1B also transduces signals of nodal, is_associated_with::GDF-1, and is_associated_with::Vg1; however, unlike activin, they require other coreceptor molecules such as the protein is_associated_with::Cripto.

Function
is_associated_with::Activins are dimeric growth and differentiation factors which belong to the is_associated_with::transforming growth factor-beta (TGF-beta) superfamily of structurally related signaling proteins. Activins signal through a heteromeric complex of receptor serine kinases which include at least two type I (I and IB) and two type II (II and IIB) receptors. These receptors are all transmembrane proteins, composed of a ligand-binding extracellular domain with a cysteine-rich region, a transmembrane domain, and a cytoplasmic domain with predicted serine/threonine specificity. Type I receptors are essential for signaling, and type II receptors are required for binding ligands and for expression of type I receptors. Type I and II receptors form a stable complex after ligand binding, resulting in is_associated_with::phosphorylation of type I receptors by type II receptors. This gene encodes activin A type IB receptor, composed of 11 exons. is_associated_with::Alternative splicing and alternative polyadenylation result in 3 fully described transcript variants. The mRNA expression of variants 1, 2, and 3 is confirmed, and a potential fourth variant contains an alternative exon 8 and lacks exons 9 through 11, but its mRNA expression has not been confirmed.

Interactions
ACVR1B has been shown to interact with
 * is_associated_with::ACVR2A, and is_associated_with::ACVR2B