Model of a trimeric SMAD5/5/4 complex binding to an ID-like composite motif on one dsDNA strand and a second GC-SBE motif at another locus. SMAD5-MH1 (dimer, green, PDB: 6FZS) and the SMAD4-MH1 (orange, PDB: 5MEY) were superimposed to docked SMAD1-MH1 and SMAD4-MH1 from a. The view highlights that the limiting factor determining binding to target motifs of BMP-sensitive SMAD complexes must be the structure of the dimeric/trimeric MH2 domains
