Abstract
Smad proteins mediate the transforming growth factor beta responses. C-terminal phosphorylation of R-Smads leads to the recruitment of Smad4 and the formation of active signaling complexes. We investigated the mechanism of phosphorylation-induced Smad complex formation with an activating pseudo-phosphorylated Smad3. Pseudo-phosphorylated Smad3 has a greater propensity to homotrimerize, and recruits Smad4 to form a heterotrimer containing two Smad3 and one Smad4. The trimeric interaction is mediated through conserved interfaces to which tumorigenic mutations map. Furthermore, a conserved Arg residue within the L3 loop, located near the C-terminal phosphorylation sites of the neighboring subunit, is essential for trimerization. We propose that the phosphorylated C-terminal residues interact with the L3 loop of the neighboring subunit to stabilize the trimer interaction.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Binding Sites
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COS Cells
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Chromatography, Gel
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Conserved Sequence
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Crystallography, X-Ray
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DNA-Binding Proteins / chemistry*
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Enzyme Activation / drug effects
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Gene Expression Regulation
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Humans
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Models, Biological
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Models, Molecular
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Peptide Fragments / chemistry
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Peptide Fragments / metabolism
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Phosphorylation / drug effects
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Protein Binding
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Protein Structure, Quaternary / drug effects
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Protein Structure, Tertiary / drug effects
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Protein Subunits
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Signal Transduction / drug effects
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Smad3 Protein
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Smad4 Protein
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Static Electricity
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Sulfates / metabolism
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Trans-Activators / chemistry*
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Trans-Activators / genetics
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Trans-Activators / metabolism*
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Transfection
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Transforming Growth Factor beta / pharmacology
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Tumor Cells, Cultured
Substances
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DNA-Binding Proteins
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Peptide Fragments
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Protein Subunits
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SMAD3 protein, human
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SMAD4 protein, human
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Smad3 Protein
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Smad4 Protein
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Sulfates
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Trans-Activators
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Transforming Growth Factor beta