Structural basis for the substrate specificity of Helix pomatia AMP deaminase and a chimeric ADGF adenosine deaminase
Bibliographic record
Abstract
Helix pomatia AMP deaminase (HPAMPD), an enzyme enriched in the foot muscle of the mollusk H. pomatia, exhibits deaminase activity on adenosine-5'-monophosphate (AMP). HPAMPD is the first member of the adenosine deaminase-related growth factor (ADGF) family to prefer the nucleotide AMP over the nucleoside adenosine. To investigate the substrate selectivity of HPAMPD, we determined its structure in both the apo form and in complex with the adenosine analogs pentostatin and pentostatin-5'-monophosphate. Structurally, HPAMPD adopts a fold similar to human ADA2, an ADGF family member. HPAMPD has acquired the ability to interact with the 5'-monophosphate group of AMP through polar and charged residues located in three key structural elements: (1) the loop immediately following strand β1; (2) the loop between helices αH and αI; and (3) the end of strand β5 and its adjacent loop. We engineered a chimeric deaminase by integrating these elements from HPAMPD into another related mollusk nucleoside adenosine deaminase, Aplysia ADGF. The chimeric enzyme efficiently deaminates AMP, demonstrating a gained substrate specificity, while retaining the adenosine deamination activity of Aplysia ADGF. The phosphate-binding feature of HPAMPD is a hallmark of nucleotide deaminases, conserved among AMP and N6-methyl-AMP (6mAMP) deaminases. We discuss the human adenosine deaminases each with distinct substrate specificities for the nucleoside, the nucleotide (AMP), and its methylated form, 6mAMP.
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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 | 0.000 | 0.001 |
| 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".