Human Activin RIA/ALK-2 Antibody

Activin isoforms and other members of the TGF-beta superfamily exert their biological effects by binding to heteromeric complexes of a type I and a type II serine‑threonine kinase receptor, both of which are essential for signal transduction. To date, seven type I and five type II receptors, including the two type I and the two type II activin receptors, designated ActR-I(A), ActR-IB, ActR-II(A), and ActR-IIB, have been cloned from mammals. Through alternative mRNA splicing, multiple ActR-IIB isoforms can also be generated, adding to the complexity of the activin receptor system. Different activin isoforms bind with different high-affinities to the various type II isoforms. Type I activin receptors do not bind directly to activin but will associate with the type II receptor-activin complex and initiate signal transduction. Besides the activin isoforms, ActR-II will also bind inhibin, BMP-2 and BMP-7 with lower affinities. ActR-I can also bind and form signaling complexes with the BMP-2/7-bound BMPR-II. Activin type I receptors are highly conserved. Human, mouse and bovine type IA activin receptors share greater than 98% amino acid sequence homology. Recombinant soluble activin type I receptor does not bind activin.