Structural Basis of Heteromeric Smad Protein Assembly in TGF-β Signaling

• Published in: Molecular cell 2004-09, Vol.15 (5), p.813-823
• Main Authors: Chacko, Benoy M., Qin, Bin Y., Tiwari, Ashutosh, Shi, Genbin, Lam, Suvana, Hayward, Lawrence J., de Caestecker, Mark, Lin, Kai
• Format: Article
• Language: English
• Subjects: Animals; Biomarkers, Tumor; COS Cells; Crystallography, X-Ray; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Hot Temperature; Macromolecular Substances; Models, Molecular; Molecular Conformation; Phosphorylation; Polymers - metabolism; Protein Structure, Tertiary; Protein Subunits - genetics; Protein Subunits - metabolism; Signal Transduction - physiology; Smad2 Protein; Smad3 Protein; Temperature; Trans-Activators - genetics; Trans-Activators - metabolism; Transforming Growth Factor beta - metabolism
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2004.07.016

The formation of protein complexes between phosphorylated R-Smads and Smad4 is a central event in the TGF-β signaling pathway. We have determined the crystal structure of two R-Smad/Smad4 complexes, Smad3/Smad4 to 2.5 Å, and Smad2/Smad4 to 2.7 Å. Both complexes are heterotrimers, comprising two phosphorylated R-Smad subunits and one Smad4 subunit, a finding that was corroborated by isothermal titration calorimetry and mutational studies. Preferential formation of the R-Smad/Smad4 heterotrimer over the R-Smad homotrimer is largely enthalpy driven, contributed by the unique presence of strong electrostatic interactions within the heterotrimeric interfaces. The study supports a common mechanism of Smad protein assembly in TGF-β superfamily signaling.