An important role for the activation peptide domain in controlling factor IX levels in the blood of haemophilia B mice
Bibliographic record
Abstract
The factors responsible for the removal of injected factor IX (fIX) from the blood of individuals with haemophilia B are only partly understood, and may include binding to endothelial or subendothelial sites, passive extravasation related to size or charge, or interactions requiring fIX activation. To investigate these issues, we have produced and characterised recombinant fIX proteins with amino acid changes: delta155-177, an internal deletion which removes most of the activation peptide while retaining the activation cleavage sites; S365A, which inactivates the serine protease activity of fIXa; and K5A, previously shown to eliminate fIX binding of endothelial/subendothelial collagen IV. All proteins were expressed in stably transfected HEK 293 cells, purified by immunoaffinity chromatography, and compared to the wild type HEK 293-derived protein (fIX (WT)). Mutant fIX proteins K5A and delta155-177 exhibited 72 and 202% of the specific activity of fIX (WT), respectively; S365A was without activity. Following intravenous injection in haemophilia B (fIX knockout) mice, recoveries did not differ for fIX (WT) and delta155-177, but were higher for K5A and S365A. The terminal catabolic half-life of delta155-177, alone among the mutants, was increased, by 45% versus fIX (WT). Nine hours post-injection, the observed areas under the clearance curve (AUCs) of delta155-177 and K5, but not S365A, were elevated 2-fold. delta155-177 was equally effective as fIX (WT) in reducing blood loss following tail vein transection in haemophilia B mice. Our results suggest that deletion of the multiple sites of fIX post-translational modification found within the activation peptide eliminated important fIX clearance motifs.
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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 | 0.000 |
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".