Exploration into the MLL4/WRAD Enzyme-Substrate Network: Systematic In Vitro Identification of CFP1 as a Potential Non-Histone Substrate of the MLL4 Lysine Methyltransferase
Bibliographic record
Abstract
Lysine methylation is a critical post-translational modification catalyzed by lysine methyltransferases (KMTs), originally characterized in the regulation of histones. However, the breadth of non-histone targets remains largely unexplored. Here, we used a systematic peptide array-based approach to define a substrate preference motif for the SET-domain-containing KMT MLL4 (KMT2D), a member of the COMPASS complex and a known H3K4 methyltransferase. Using this motif, we identified CXXC finger protein 1 (CFP1), a core component of Setd1A/B complexes, as a putative MLL4 substrate. In vitro methyltransferase assays confirmed robust methylation of CFP1 by an MLL4-WRAD complex. Surprisingly, while initial predictions implicated K328, array-based methylation profiling revealed multiple lysine residues within CFP1's lysine-rich basic domain as methylation targets, including K331, K335, K339, and K340. We further demonstrated that CFP1 methylation likely modulates its interaction with MLL4's PHD cassettes and facilitates binding to Setd1A. Binding preferences of MLL4's PHD1-3 and PHD4-6 domains varied with methylation state and site, suggesting non-histone methyl mark recognition by these cassettes. Pulldown assays confirmed that methylated, but not unmethylated, CFP1 binds Setd1A, supporting a potential methyl-switch mechanism. Together, our findings propose CFP1 as a potential non-histone substrate of MLL4 and suggest that MLL4 may regulate Setd1A/B function indirectly via CFP1 methylation. This study expands the substrate landscape of MLL4 and lays the groundwork for future investigations into non-histone methylation signaling in chromatin regulation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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 source (direct Gemma or distilled Codex), 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".