Cholesterol Is Found To Reside in the Center of a Polyunsaturated Lipid Membrane
Bibliographic record
Abstract
Previously, we reported neutron diffraction studies on the depth of cholesterol in phosphatidylcholine (PC) bilayers with varying amounts of acyl chain unsaturation [Harroun, T. A., et al. (2006) Biochemistry 45, 1227-1233]. The center of mass of the 2,2,3,4,4,6-D 6 deuterated sites on the sterol label was found to reside 16 A from the middle of the bilayer in 1-palmitoyl-2-oleoylphosphatidylcholine (16:0-18:1PC), 1,2-dioleoylphosphatidylcholine (18:1-18:1PC), and 1-stearoyl-2-arachidonylphosphatidylcholine (18:0-20:4PC). This location places cholesterol's hydroxyl group close to the membrane surface, indicative of the molecule in its commonly understood "upright" orientation. However, for dipolyunsaturated 20:4-20:4PC membranes the label, thus the hydroxyl group, was found sequestered in the center of the bilayer. We attributed the change in location to the high level of disorder of polyunsaturated fatty acids (PUFA) that is incompatible with proximity to the rigid steroid moiety in its usual upright orientation. From that study, the unresolved question was whether the molecule was inverted or lying flat with respect to the membrane plane, in the middle of the bilayer. We have followed up those results with additional neutron experiments employing [25,26,26,26,27,27-D 7]cholesterol, a deuterated analogue labeled in the tail. These diffraction measurements unequivocally show cholesterol lies flat in the middle of 20:4-20:4PC bilayers.
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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 | 0.001 |
| 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".