Conserved tryptophan in cytochrome c: importance of the unique side-chain features of the indole moiety
Bibliographic record
Abstract
The absolute conservation of tryptophan at position 59 in cytochrome c is related to the unique chemical nature of its indole moiety. The indole side chain of Trp-59 possesses three salient features: bulk, hydrophobicity and the ability of its indole nitrogen to act as a hydrogen-bond donor. Crystallographic evidence identifies the indole nitrogen of Trp-59 as having a stabilizing hydrogen-bonding interaction with the buried carboxylate group of haem propionate 7. Side-chain bulk is also likely to be important because a Phe or Leu residue can replace Trp to give an at least partly functional protein, whereas the smaller Gly or Ser cannot. Semisynthetic analogues were designed to test the importance of the side-chain features of tryptophan by using a recently developed method for stereoselective fragment religation in yeast cytochrome c. Three yeast iso-1 cytochrome c analogues were produced in which Trp-59 was replaced by a non-coded amino acid: p-iodophenylalanine, β-(3-pyridyl)-alanine or β-(2-naphthyl)-alanine. Replacement of Trp-59 with these non-coded amino acids allows the reasons for its conservation to be analysed, because they vary with respect to size, hydrophobicity and hydrogen-bond potential. Our results show that decreasing the bulk and hydrophobicity of the side chain at position 59 has a profound but different impact on physicochemical and biological parameters from those of abolishing hydrogen-bond donor potential. This suggests that Trp-59 has both a local and a global stability effect by solvating a buried charge and by having a key role in the packing of the cytochrome c hydrophobic core.
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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 | 0.000 |
| 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".