Role of the N-terminal Proline Residue in the Catalytic Activities of the Escherichia coli Fpg Protein
Bibliographic record
Abstract
The Escherichia coli Fpg protein is a DNA glycosylase/AP lyase. It removes, in DNA, oxidized purine residues, including the highly mutagenic C8-oxo-guanine (8-oxoG). The catalytic mechanism is believed to involve the formation of a transient Schiff base intermediate formed between DNA containing an oxidized residue and the N-terminal proline of the Fpg protein. The importance and the role of this proline upon the various catalytic activities of the Fpg protein was examined by targeted mutagenesis, resulting in the construction of three mutant Fpg proteins: Pro-2 --> Gly (FpgP2G), Pro-2 --> Thr (FpgP2T), and Pro-2 --> Glu (FpgP2E). The formamidopyrimidine DNA glycosylase activities of FpgP2G and FpgP2T were comparable and accounted for 10% of the wild-type activity. FpgP2G and FpgP2T had barely detectable 8-oxoG-DNA glycosylase activity and produced minute Schiff base complex with 8-oxoG/C DNA. FpgP2G and FpgP2T mutants did not cleave a DNA containing preformed AP site but readily produced Schiff base complex with this substrate. FpgP2E was completely inactive in all the assays. The binding constants of the different mutants when challenged with a duplex DNA containing a tetrahydrofuran residue were comparable. The mutant Fpg proteins barely or did not complement in vivo the spontaneous transitions G/C --> T/A in E. coli BH990 (fpg mutY) cells. These results show the mandatory role of N-terminal proline in the 8-oxoG-DNA glycosylase activity of the Fpg protein in vitro and in vivo as well as in its AP lyase activity upon preformed AP site but less in the 2,6-diamino-4-hydroxy-5-N-methylformamidopyrimidine-DNA glycosylase activity.
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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) | 0.001 | 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 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".