Biochemical analysis of a Ca<sup>2+</sup>‐dependent membrane–membrane interaction mediated by the sea urchin yolk granule protein, toposome
Bibliographic record
Abstract
Toposome, a high molecular mass protein, is an abundant component of the yolk granule in the sea urchin egg and embryo. Toposome is composed of a 160 kDa polypeptide that is proteolytically processed into smaller species of 120 and 90 kDa during embryonic development. The exact biological function of toposome during early development is unknown. In this study we have examined calcium binding to toposome and the effect of this binding on the secondary and tertiary structural characteristics of the purified protein. Initially, we used equilibrium dialysis to quantify calcium binding to toposome. Monophasic binding of up to 600 M of calcium per mole of protein was detected with an intrinsic dissociation constant (calcium) of 240 microm. Increasing concentrations of calcium resulted in an increase in alpha helical content from 3.0 to 22.0%, which occurred with an apparent dissociation constant (calcium) of 25 microm. In parallel experiments, toposome binding to liposomes required similar concentrations of calcium; an apparent dissociation constant (calcium) of 25 microm was recorded. Endogenous tryptophan fluorescence measurements, both in the presence and absence of liposomes, demonstrated that the tertiary structure is sensitive to increasing concentrations of calcium with an apparent dissociation constant (calcium) of 240 microm. Toposome-driven, liposome aggregation assays revealed a similar calcium requirement. Collectively, these results define a two-step model for calcium modulation of toposome structure and function.
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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".