Abstract 417: Structural Characterization of 20 kDa Fragments of Apolipoprotein B100
Bibliographic record
Abstract
Apolipoprotein (apo) B100 is a 550 kDa hydrophobic glycoprotein that forms the structural backbone for the assembly of triglyceride-rich lipoproteins. ApoB100 circulates bound to the same lipoprotein particle on which it is synthesized (i.e. it is non-exchangeable) until the lipoprotein is cleared from the plasma via receptor-mediated uptake. The polypeptide length and aqueous insolubility are considerable obstacles to the determination of apoB100 structure. Based on primary structure algortihms, apoB100 is predicted to contain 5 domains, comprising an N-terminal globular mixed βα1 domain followed by alternating amphipathic β-strand and α-helix rich regions (N-βα1-β1-α2-β2-α3-C). Previous studies from our laboratory have shown that amino acids 1694-1880 (B1) of the β1 domain of apoB100 bind tightly to triglyceride droplets in vitro. We have expressed this 20 kDa protein fragment, and a second 20 kDa fragment B2 (amino acids 1881-2070) that lies at the junction between the β1 and α2 domains, in bacterial cell culture as hexahistidine-tagged fusion proteins. B1 was insoluble in aqueous solution, but soluble in the presence of 150 mM dodecylphosphocholine (DPC), whereas B2 was soluble in aqueous solution, with or without DPC. Circular dichroism (CD) spectroscopy of DPC-solubilized B1 and B2 fragments indicated an approximately equal proportion of α-helix, β-strand/β-turn and unordered structures in B1 (36%, 37% and 28%, respectively) vs. approximately 56% α-helix, 27% β-strand/β-turn and 17% unordered content for B2. Preliminary NMR spectroscopy of 13C/15N labeled B1 has been conducted. Estimates of protein secondary structure from backbone chemical shift assignments using the algorithm DANGLE (Dihedral ANgles from Global Likelihood Estimates) suggested significant α-helical character in B1. These studies suggest that the α-helical content may be underestimated by CD, and generation of a high-resolution structure of B1 is in progress. Our studies have provided the first atomic-level structural information for structural elements of apoB100 and suggest a central role for unique amphipathic structures in lipoprotein structure and function.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".