Signal Processing in the TGF-β Superfamily Ligand-Receptor Network
Figure 1
Formation of Receptor Hetero-Tetramers
The active form of the TGF-β ligand is a dimer of two molecules held together by hydrophobic interactions and a disulfide bond [30,31]. This dimer induces the formation, at the plasma membrane, of receptor hetero-tetramers that contain two type I and two type II receptors [2,3]. The type II receptors phosphorylate the type I receptors; the type I receptors are then enabled to phosphorylate cytoplasmic R-Smads, which then act as transcriptional regulators.