title: Structural basis of heteromeric smad protein assembly in TGF-beta signaling.
abstract: The formation of protein complexes between phosphorylated R-Smads and Smad4 is a central event in the TGF-beta signaling pathway. We have determined the crystal structure of two R-Smad/Smad4 complexes, Smad3/Smad4 to 2.5 angstroms, and Smad2/Smad4 to 2.7 angstroms. 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-beta superfamily signaling.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Benoy M
authors.initials: BM
authors.lastname: Chacko
authors.forename: Bin Y
authors.initials: BY
authors.lastname: Qin
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Tiwari
authors.forename: Genbin
authors.initials: G
authors.lastname: Shi
authors.forename: Suvana
authors.initials: S
authors.lastname: Lam
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Hayward
authors.forename: Mark
authors.initials: M
authors.lastname: De Caestecker
authors.forename: Kai
authors.initials: K
authors.lastname: Lin
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor; D019556:COS Cells; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D046911:Macromolecular Substances; D008958:Models, Molecular; D008968:Molecular Conformation; D010766:Phosphorylation; D011108:Polymers / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein; D051900:Smad3 Protein; D013696:Temperature; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D000951:Antigens, Neoplasm
chemical_list: D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D011108:Polymers; D021122:Protein Subunits; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C115012:human epithelial antigen-125; D000951:Antigens, Neoplasm