Regulation of Smurf2 ubiquitin ligase activity by anchoring the E2 to the HECT domain.
The conjugation of ubiquitin to proteins involves a cascade of activating (E1), conjugating (E2), and ubiquitin-ligating (E3) type enzymes that commonly signal protein destruction. In TGFbeta signaling the inhibitory protein Smad7 recruits Smurf2, an E3 of the C2-WW-HECT domain class, to the TGFbeta receptor complex to facilitate receptor degradation. Here, we demonstrate that the amino-terminal domain (NTD) of Smad7 stimulates Smurf activity by recruiting the E2, UbcH7, to the HECT domain. A 2.1 A resolution X-ray crystal structure of the Smurf2 HECT domain reveals that it has a suboptimal E2 binding pocket that could be optimized by mutagenesis to generate a HECT domain that functions independently of Smad7 and potently inhibits TGFbeta signaling. Thus, E2 enzyme recognition by an E3 HECT enzyme is not constitutively competent and provides a point of control for regulating the ubiquitin ligase activity through the action of auxiliary proteins.
Pubmed ID: 16061177 RIS Download
Amino Acid Motifs | Amino Acid Sequence | Binding Sites | Catalysis | Cell Line | Crystallography, X-Ray | DNA-Binding Proteins | Enzyme Activation | Humans | Models, Molecular | Molecular Sequence Data | Mutagenesis, Site-Directed | Mutation | Peptide Fragments | Protein Binding | Protein Structure, Tertiary | Receptors, Transforming Growth Factor beta | Recombinant Proteins | Sequence Homology, Amino Acid | Signal Transduction | Smad7 Protein | Trans-Activators | Transfection | Ubiquitin | Ubiquitin-Activating Enzymes | Ubiquitin-Conjugating Enzymes | Ubiquitin-Protein Ligases