Characterizing the Size and Composition of Saposin A Lipoprotein Picodiscs
Bibliographic record
Abstract
Saposin A (SapA) lipoprotein discs, also known as picodiscs (PDs), represent an attractive method to solubilize glycolipids for protein interaction studies in aqueous solution. Recent electrospray ionization mass spectrometry (ESI-MS) data suggest that the size and composition of 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphocholine (POPC)-containing PDs at neutral pH differs from those of N, N -dimethyldodecylamine N -oxide determined by X-ray crystallography. Using high-resolution ESI-MS, multiangle laser light scattering (MALLS), and molecular dynamics (MD) simulations, the composition, heterogeneity, and structure of POPC–PDs in aqueous ammonium acetate solutions at pH 4.8 and 6.8 were investigated. The ESI-MS and MALLS data revealed that POPC–PDs consist predominantly of (SapA dimer + i POPC) complexes, with i = 23–29, and have an average molecular weight (MW) of 38.2 ± 3.3 kDa at pH 4.8. In contrast, in freshly prepared solutions at pH 6.8, POPC–PDs are composed predominantly of (SapA tetramer + i POPC) complexes, with i = 37–60, with an average MW of 68.0 ± 2.7 kDa. However, the (SapA tetramer + i POPC) complexes are unstable at neutral pH and convert, over a period of hours, to (SapA trimer + i POPC) complexes, with i = 29–36, with an average MW of 51.1 ± 2.9 kDa. The results of molecular modeling suggest spheroidal structures for the (SapA dimer + i POPC), (SapA trimer + i POPC), and (SapA tetramer + i POPC) complexes in solution. Comparison of measured collision cross sections (Ω) with values calculated for gaseous (SapA dimer + 26POPC) 8+, (SapA trimer + 33POPC) 12+, and (SapA tetramer + 42POPC) 16+ ions produced from modeling suggests that the solution structures are largely preserved in the gas phase, although the lipids do not maintain regular bilayer orientations.
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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".