Two short segments of Smad3 are important for specific interaction of Smad3 with c-Ski and SnoN.
c-Ski and SnoN are transcriptional co-repressors that inhibit transforming growth factor-beta signaling through interaction with Smad proteins. Among receptor-regulated Smads, c-Ski and SnoN bind more strongly to Smad2 and Smad3 than to Smad1. Here, we show that c-Ski and SnoN bind to the "SE" sequence in the C-terminal MH2 domain ... of Smad3, which is exposed on the N-terminal upper side of the toroidal structure of the MH2 oligomer. The "QPSMT" sequence, located in the vicinity of SE, supports the interaction with c-Ski and SnoN. Sequences similar to SE and QPSMT are found in Smad2, but not in Smad1. The N-terminal MH1 domain and linker region of Smad3 protrude from the N-terminal upper side of the MH2 oligomer toroid. Smurf2 induces ubiquitin-dependent degradation of SnoN, since it appears to be located close to SnoN through binding to the linker region of Smad2. In contrast, transcription factors Mixer and FoxH3 (FAST1) bind to the bottom side of the Smad3 MH2 toroid; therefore, c-Ski does not affect the interaction of Smads with these transcription factors. Our findings thus demonstrate the stoichiometry of how multiple molecules can associate with the Smad oligomers and how the Smad-interacting proteins functionally interact with each other.
Mesh Terms:
Activin Receptors, Type I, Amino Acid Sequence, Animals, Binding Sites, Bone Morphogenetic Protein Receptors, Type I, COS Cells, DNA-Binding Proteins, Humans, Intracellular Signaling Peptides and Proteins, Ligases, Macromolecular Substances, Models, Molecular, Molecular Sequence Data, Protein Binding, Protein Conformation, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Receptors, Growth Factor, Receptors, Transforming Growth Factor beta, Recombinant Fusion Proteins, Repressor Proteins, Sequence Alignment, Signal Transduction, Smad3 Protein, Trans-Activators, Transcription Factors, Transforming Growth Factor beta, Ubiquitin, Ubiquitin-Protein Ligases
Activin Receptors, Type I, Amino Acid Sequence, Animals, Binding Sites, Bone Morphogenetic Protein Receptors, Type I, COS Cells, DNA-Binding Proteins, Humans, Intracellular Signaling Peptides and Proteins, Ligases, Macromolecular Substances, Models, Molecular, Molecular Sequence Data, Protein Binding, Protein Conformation, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Receptors, Growth Factor, Receptors, Transforming Growth Factor beta, Recombinant Fusion Proteins, Repressor Proteins, Sequence Alignment, Signal Transduction, Smad3 Protein, Trans-Activators, Transcription Factors, Transforming Growth Factor beta, Ubiquitin, Ubiquitin-Protein Ligases
J. Biol. Chem.
Date: Jan. 03, 2003
PubMed ID: 12426322
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