Biochemical Characterization of the Roles of Glycines 24 and 27 and Threonine 179 in Tropomyosin from the Fast Skeletal Trunk Muscle of the Atlantic Salmon
Bibliographic record
Abstract
Atlantic salmon fast skeletal muscle is composed of an α-type tropomyosin that shares 20 substitutions with a mammalian homologue. Prominent isomorphisms considered to be potentially destabilizing include threonine 179 (core, Ala in rabbit) and a unique pair of glycines, residues 24 and 27. Bacterially expressed mutant tropomyosins were isolated without exposure to elevated temperature or organic solvent. The Thr179Ala mutant is more resistant to heat-induced denaturation (Tm > 40 °C) than the nonmutant control (Tm = 37 °C) as monitored by far-UV circular dichroism [0.1 M salt and 1 mM DTT (pH 7)]. Changing one glycine to alanine has no detectable effect on the Tm versus the control value. An increase of 1 °C is observed for the double mutant (Gly27Ala/Gly24Ala). The preferred site of chymotryptic cleavage of recombinant salmon tropomyosin is between Leu 11 and Lys 12. The rate of the subsequent cleavage at Leu 169, the preferred site in rabbit tropomyosin, is reduced via replacement of Thr 179 with Ala. Thin filaments reconstituted with this mutant display greater Ca(II) induction of the myosin steady-state MgATPase versus control. Glycine-induced local instability is demonstrated by Escherichia coli outer membrane protease T (Omp-T) cleavage between Lys 6 and Lys 7. The control is more susceptible to proteolysis at this site than the mutants, which are distinct from each other: control > Gly27Ala > Gly24Ala > double mutant (most resistant to Omp-T). Similarly, the double mutant is comparatively more resistant to cleavage at Leu 11. By inference, the mid- and amino-terminal sections of salmon tropomyosin are intrinsically less stable than those in mammals, suggesting greater flexibility. Neighboring glycines make up a new destabilization motif in tropomyosin.
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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) | 0.001 | 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".