TGIF1 homeodomain interacts with Smad MH1 domain and represses TGF-β signaling

Nucleic Acids Res. 2018 Sep 28;46(17):9220-9235. doi: 10.1093/nar/gky680.


TGIF1 is a multifunctional protein that represses TGF-β-activated transcription by interacting with Smad2-Smad4 complexes. We found that the complex structure of TGIF1-HD bound to the TGACA motif revealed a combined binding mode that involves the HD core and the major groove, on the one hand, and the amino-terminal (N-term) arm and the minor groove of the DNA, on the other. We also show that TGIF1-HD interacts with the MH1 domain of Smad proteins, thereby indicating that TGIF1-HD is also a protein-binding domain. Moreover, the formation of the HD-MH1 complex partially hinders the DNA-binding site of the complex, preventing the efficient interaction of TGIF1-HD with DNA. We propose that the binding of the TGIF1 C-term to the Smad2-MH2 domain brings both the HD and MH1 domain into close proximity. This local proximity facilitates the interaction of these DNA-binding domains, thus strengthening the formation of the protein complex versus DNA binding. Once the protein complex has been formed, the TGIF1-Smad system would be released from promoters/enhancers, thereby illustrating one of the mechanisms used by TGIF1 to exert its function as an active repressor of Smad-induced TGF-β signaling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Cloning, Molecular
  • Crystallography, X-Ray
  • DNA / chemistry*
  • DNA / genetics
  • DNA / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Expression
  • Gene Expression Regulation
  • Genetic Vectors / chemistry
  • Genetic Vectors / metabolism
  • Homeodomain Proteins / chemistry*
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism
  • Humans
  • Models, Molecular
  • Nucleotide Motifs
  • Protein Binding
  • Protein Conformation, alpha-Helical
  • Protein Conformation, beta-Strand
  • Protein Interaction Domains and Motifs
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Repressor Proteins / chemistry*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Smad2 Protein / chemistry*
  • Smad2 Protein / genetics
  • Smad2 Protein / metabolism
  • Smad4 Protein / chemistry*
  • Smad4 Protein / genetics
  • Smad4 Protein / metabolism
  • Transforming Growth Factor beta / chemistry*
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism


  • Homeodomain Proteins
  • Recombinant Proteins
  • Repressor Proteins
  • SMAD2 protein, human
  • SMAD4 protein, human
  • Smad2 Protein
  • Smad4 Protein
  • TGIF1 protein, human
  • Transforming Growth Factor beta
  • DNA