Formation of the hetero-tetrameric BMP2:receptor complex induces receptor rotation, so that their cytoplasmic kinase domains face each other in a catalytically favourable configuration. The constitutively active type II receptor kinase (which auto-phosphorylates in the absence of ligand), trans-phosphorylates specific serine residues at the conserved Gly-Ser-rich juxtapositioned domain of the type I receptor. It is not known if exactly 8 ATPs are required for the phosphorylation of type I receptor, there could be more or less than this number.
ten Dijke, P,
activin receptor activity, type II of BMP:BMPRII:BMPRI [plasma membrane]