title: Regulation of Smurf2 ubiquitin ligase activity by anchoring the E2 to the HECT domain.
abstract: 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.
authors.affiliation: Programme in Molecular Biology and Cancer, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada.
authors.forename: Abiodun A
authors.initials: AA
authors.lastname: Ogunjimi
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Briant
authors.forename: Nadia
authors.initials: N
authors.lastname: Pece-Barbara
authors.forename: Christine
authors.initials: C
authors.lastname: Le Roy
authors.forename: Gianni M
authors.initials: GM
authors.lastname: Di Guglielmo
authors.forename: Peter
authors.initials: P
authors.lastname: Kavsak
authors.forename: Richele K
authors.initials: RK
authors.lastname: Rasmussen
authors.forename: Bruce T
authors.initials: BT
authors.lastname: Seet
authors.forename: Frank
authors.initials: F
authors.lastname: Sicheri
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Wrana
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D002460:Cell Line; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004789:Enzyme Activation; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010446:Peptide Fragments / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D010446:Peptide Fragments; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; C497806:SMAD7 protein, human; D051906:Smad7 Protein; D015534:Trans-Activators; D025801:Ubiquitin; C079437:UBE2L3 protein, human; D044763:Ubiquitin-Conjugating Enzymes; C471641:SMURF2 protein, human; D044767:Ubiquitin-Protein Ligases; D044764:Ubiquitin-Activating Enzymes