Intrinsic Fluorescence Reports a Global Conformational Change in the N-Lobe of Human Serum Transferrin following Iron Release†
Bibliographic record
Abstract
Transferrins have been extensively studied in order to understand how they reversibly bind and release iron. Human serum transferrin (hTF) is a single polypeptide chain that folds into two lobes (N- and C-lobe); each lobe binds a single ferric ion. Iron release induces a large conformational change in each lobe. At the putative endosomal pH of 5.6, measurement of the increase in intrinsic fluorescence upon iron release from the recombinant N-lobe yields two rate constants: 8.9 min-1 and 1.3 min-1. Direct monitoring of iron release from the N-lobe at pH 5.6 (by the decrease in absorbance at 470 nm) gives a single rate constant of 9.1 min-1, definitively establishing that the faster rate constant in the fluorescent studies is due to iron release. To further elucidate the molecular basis of the intrinsic fluorescence change (and the source of the slower rate constant), we examined the contributions of the three individual tryptophan residues in the N-lobe (Trp8, Trp128, and Trp264). Three double mutants, each containing the single remaining tryptophan residue, were produced. In the iron-bound N-lobe, Trp128 and Trp264 are quenched by iron and account for almost the entire fluorescent signal when iron is released. As for the wild-type N-lobe, the fluorescence increase for each of these mutants is best fit by a double-exponential function indicating two processes. Trp8 is severely quenched under all conditions, making virtually no contribution to the signal. Additionally, a mutant lacking all three Trp residues allows assignment of the fluorescent signal completely to the three tryptophan residues and observation of the presence of one (or more) tyrosinates in the N-lobe that have physiological significance in the uptake of iron.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".