Can localized impurities exert global effects on lipid model membranes
Bibliographic record
Abstract
The currently accepted model for cell membrane organization involves "lipid rafts"', which differ in composition from the surrounding lipid sea. The existence of these nano-scale heterogeneities is supported by observation of coexisting ordered and disordered lipid phases in lipid model membranes. Fluorescence is a popular family of techniques that can provide dynamic and structural information about membranes. With any probe method, characterization of the effects of fluorescent probe addition on the systems they are used to study is important for the interpretation of experimental data. Comparison can be made between labelled and unlabelled samples using a non-perturbing method, such as deuterium nuclear magnetic resonance spectroscopy (2H NMR). This thesis used 2H NMR to study the effects of an equipartitioning probe, Laurdan, and a non-equipartitioning probe, naphthopyrene, on a well-studied three-component lipid membrane system (35:35:30 dioleoyl-sn-glycero-3-phosphocholine (DOPC)/dipalmitoyl-sn-glycero-3-phosphocholine-D62 (DPPC-D62)/cholesterol) with a miscibility phase transition. In phase-separated membranes, 0.03-0.6% naphthopyrene disordered lipid chains of DPPC-D62 in the liquid-disordered phase, but not of those in the liquid-ordered phase. 0.1-2% Laurdan did not affect the DPPC-D62 in either phase in these membranes. Above the miscibility transition temperature (22 degrees Celsius), there is a single homogeneous liquid phase that is not perturbed by the addition of either probe. Laurdan is particularly well suited to the study of phase separation in lipid membranes. It partitions equally well into ordered and disordered lipid phases and displays a polarity-dependent emission spectral shift. Laurdan general polarization (GP) parameter, which characterizes said spectral shift, has been used to characterize membrane fluidity. Two-photon excitation microscopy Laurdan GP images were acquired for membranes with 0.2-2% Laurdan, and Laurdan GP values were found to be strongly correlated with dnmr methylene order parameters of DPPC-D62 in the liquid-ordered phase. Finally, photo-induced phase separation is known to occur in fluorescence microscopy experiments; however, our 2H NMR experiments showed that naphthopyrene can alter membrane properties in the absence of light. The fact that trace amounts of probe (e.g., 0.03-0.6% naphthopyrene) affect lipid molecular order has biological implications: biomolecules present in very small amounts are known to have important functions in cells.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".