Structural Basis for the Superior Activity of the Large Isoform of Snow Flea Antifreeze Protein
Bibliographic record
Abstract
The snow flea (Hypogastrum harveyi) is protected from freezing at sub-zero temperatures by a glycine-rich antifreeze protein (AFP) that binds to seed ice crystals and prevents them from growing larger. This AFP is hyperactive and comprises two isoforms [Graham, L. A., and Davies, P. L. (2005) Science 310, 461]. The larger isoform (15.7 kDa) exhibits several-fold higher activity than the smaller isoform (6.5 kDa), although it is considerably less abundant. To establish the molecular basis for this difference in activity, we determined the sequence of the large isoform. The primary sequences of these two isoforms are surprisingly divergent. However, both contain tripeptide repeats and turn motifs that enabled us to build a three-dimensional model of the large isoform based upon the six-polyproline helix structure of the small isoform. Our model contains 13 polyproline type II helices connected by proline-containing loops stacked into two flat sheets oriented antiparallel to one another. The structure is strictly amphipathic, with a hydrophilic surface on one side and a hydrophobic, putative ice-binding surface on the other. The putative ice-binding site is approximately twice as large in area as that of the small isoform, providing an explanation for the difference in activity that is consistent with other examples noted. By tagging the recombinant AFP with green fluorescent protein, we observed its binding to multiple planes of ice, especially the basal plane. This finding supports the correlation between AFP hyperactivity and basal plane binding first observed with spruce budworm AFP.
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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".