Spectral and metal-binding properties of three single-point tryptophan mutants of the human transferrin N-lobe
Bibliographic record
Abstract
Human serum transferrin N-lobe (hTF/2N) contains three conserved tryptophan residues, Trp(8), Trp(128) and Trp(264), located in three different environments. The present report addresses the different contributions of the three tryptophan residues to the UV-visible, fluorescence and NMR spectra of hTF/2N and the effect of the mutations at each tryptophan residue on the iron-binding properties of the protein. Trp(8) resides in a hydrophobic box containing a cluster of three phenylalanine side chains and is H bonded through the indole N to an adjacent water cluster lying between two beta-sheets containing Trp(8) and Lys(296) respectively. The fluorescence of Trp(8) may be quenched by the benzene rings. The apparent increase in the rate of iron release from the Trp(8)-->Tyr mutant could be due to the interference of the mutation with the H-bond linkage resulting in an effect on the second shell network. The partial quenching in the fluorescence of Trp(128) results from the nearby His(119) residue. Difference-fluorescence spectra reveal that any protein containing Trp(128) shows a blue shift upon binding metal ion, and the NMR signal of Trp(128) broadens out and disappears upon the binding of paramagnetic metals to the protein. These data imply that Trp(128) is a major fluorescent and NMR reporter group for metal binding, and possibly for cleft closure in hTF/2N. Trp(264) is located on the surface of the protein and does not connect to any functional residues. This explains the facts that Trp(264) is the major contributor to both the absorbance and fluorescence spectra, has a strong NMR signal and the mutation at Trp(264) has little effect on the iron-binding and release behaviours of the protein.
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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 | 0.000 |
| 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".