An expanded WW domain recognition motif revealed by the interaction between Smad7 and the E3 ubiquitin ligase Smurf2.
Smurf2 is an E3 ubiquitin ligase that drives degradation of the transforming growth factor-beta receptors and other targets. Recognition of the receptors by Smurf2 is accomplished through an intermediary protein, Smad7. Here we have demonstrated that the WW3 domain of Smurf2 can directly bind to the Smad7 polyproline-tyrosine (PY) motif. Of particular interest, the highly conserved WW domain binding site Trp, which interacts with target PY motifs, is a Phe in the Smurf2 WW3 domain. To examine this interaction, the solution structure of the complex between the Smad7 PY motif region (ELESPPPPYSRYPMD) and the Smurf2 WW3 domain was determined. The structure reveals that, in addition to binding the PY motif, the WW3 domain binds six residues C-terminal to the PY motif (PY-tail). Although the Phe in the WW3 domain binding site decreases affinity relative to the canonical Trp, this is balanced by additional interactions between the PY-tail and the beta1-strand and beta1-beta2 loop of the WW3 domain. The interaction between the Smurf2 WW3 domain and the Smad7 PY motif is the first example of PY motif recognition by a WW domain with a Phe substituted for the binding site Trp. This unusual interaction allows the Smurf2 WW3 domain to recognize a subset of PY motif-containing proteins utilizing an expanded surface to provide specificity.
Chong
P Andrew
PA
Program in Structural Biology and Biochemistry, Hospital for Sick Children, Toronto M5G 1X8; Department of Medical Genetics and Microbiology, University of Toronto, Toronto M5S 1A8.
Lin
Hong
H
Program in Structural Biology and Biochemistry, Hospital for Sick Children, Toronto M5G 1X8.
Wrana
Jeffrey L
JL
Department of Medical Genetics and Microbiology, University of Toronto, Toronto M5S 1A8; Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto M5G 1X5.
Forman-Kay
Julie D
JD
Program in Structural Biology and Biochemistry, Hospital for Sick Children, Toronto M5G 1X8; Department of Biochemistry, University of Toronto, Toronto M5S 1A8, Canada. Electronic address: forman@sickkids.ca.
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D051906:Smad7 Protein / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry*
C497806:SMAD7 protein, human; D051906:Smad7 Protein; D014364:Tryptophan; C471641:SMURF2 protein, human; D044767:Ubiquitin-Protein Ligases