Catalytic domain of Transforming Growth Factor beta Receptor-like Serine/Threonine Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. This subfamily is composed of receptors for the TGFbeta family of secreted signaling molecules including TGFbeta, bone morphogenetic proteins (BMPs), activins, growth and differentiation factors (GDFs), and anti-Mullerian hormone, among others. These receptors contain an extracellular domain that binds ligands, a single transmembrane (TM) region, and a cytoplasmic catalytic kinase domain. There are two types of TGFbeta receptors included in this subfamily, I and II, that play different roles in signaling. For signaling to occur, the ligand first binds to the high-affinity type II receptor, which is followed by the recruitment of the low-affinity type I receptor to the complex and its activation through trans-phosphorylation by the type II receptor. The active type I receptor kinase starts intracellular signaling to the nucleus by phosphorylating SMAD proteins. Type I receptors contain an additional domain located between the TM and kinase domains called the the GS domain, which contains the activating phosphorylation site and confers preference for specific SMAD proteins. Different ligands interact with various combinations of types I and II receptors to elicit a specific signaling pathway. Activins primarily signal through combinations of ACVR1b/ALK7 and ACVR2a/b; myostatin and GDF11 through TGFbR1/ALK4 and ACVR2a/b; BMPs through ACVR1/ALK1 and BMPR2; and TGFbeta through TGFbR1 and TGFbR2. The TGFbR-like subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",