 The amino acid (aa) region 437–558 in the extracellular domain of endoglin will bind to TGF beta receptor II.TGF beta receptor I binds to the 437-588 aa region and to the aa region between 437 and the N-terminus.Unlike TGF beta receptor I which can only bind the cytoplasmic tail when its kinase domain is inactive, TGF beta receptor II can bind endoglin with an inactive and active kinase domain.