Artisanal Production of Prefusion-Stabilized SARS-CoV-2 Spikes v1
Bibliographic record
Abstract
The two-part protocol presented here describes the establishment of a stable pool of 293-F cells expressing the HexaPro variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) spike (S) protein and its production and purification from the culture medium. CRISPR-Cas9-driven targeted integration of the expression cassette at the AAVS1 safe harborlocus streamlines cell line production. Engineered 293-F cells grown as suspension cultures in animal origin-free, chemically defined, protein-free medium allow purification to be performed directly from the culture medium with minimal cell processing steps. Yields of native and purified Spikes typically average 30-50 mg per liter of culture medium following tandem affinity purification using nickel-coupled and Strep-Tactin resins. Purified proteins bind recombinant ACE2 and mAb CR3022 in ELISA-based assays. Establishing an engineered cell line from cryopreserved 293-F cells takes approximately 4 weeks, and subsequent production and purification take between 9 and 14 days. As shown for the D614G mutation, this system can be readily adapted to study Spike variants.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 0.009 |
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".