The TGF-β Superfamily is comprised of several smaller families of structurally related regulatory proteins. Mature, active forms of these proteins are generally present as homodimers, but heterodimers may also occur. TGF-β Superfamily members usually interact with type I and II serine/threonine-specific protein kinase receptors at the cell surface and activate Smad signaling pathways. Non-Smad signaling can also occur through activation of other molecules such as Akt, MAPK, mTOR and Src. Members of the TGF-β Superfamily play diverse roles during growth, development, differentiation and tissue homeostasis. Certain members have been classified as morphogens, as their effects were found to be a function of concentration.
The TGF-β Superfamily is comprised of the Activin, BMP, GDF, GDNF, Smad and TGF-β families.