An Expanded WW Domain Recognition Motif Revealed by the Interaction between Smad7 and the E3 Ubiquitin Ligase Smurf2
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".