Identification of a Lipoprotein Lipase Cofactor-binding Site by Chemical Cross-linking and Transfer of Apolipoprotein C-II-responsive Lipolysis from Lipoprotein Lipase to Hepatic Lipase
Bibliographic record
Abstract
To localize the regions of lipoprotein lipase (LPL) that are responsive to activation by apoC-II, an apoC-II peptide fragment was cross-linked to bovine LPL. Following chemical hydrolysis and peptide separation, a specific fragment of LPL (residues 65-86) was identified to interact with apoC-II. The fragment contains regions of amino acid sequence dissimilarity compared with hepatic lipase (HL), a member of the same gene family that is not responsive to apoC-II. Using site-directed mutagenesis, two sets of chimeras were created in which the two regions of human LPL (residues 65-68 and 73-79) were exchanged with the corresponding human HL sequences. The chimeras consisted of an HL backbone with the suspected LPL regions replacing the corresponding HL sequences either individually (HLLPL-(65-68) and HLLPL-(73-79)) or together (HLLPLD). Similarly, LPL chimeras were created in which the candidate regions were replaced with the corresponding HL sequences (LPLHL-(77-80), LPLHL-(85-91), and LPLHLD). Using a synthetic triolein substrate, the lipase activity of the purified enzymes was measured in the presence and absence of apoC-II. Addition of apoC-II to HLLPL-(65-68) and HLLPL-(73-79) did not significantly alter their enzyme activity. However, the activity of HLLPLD increased approximately 5-fold in the presence of apoC-II compared with an increase in native LPL activity of approximately 11-fold. Addition of apoC-II to LPLHL-(77-80) resulted in approximately 10-fold activation, whereas only approximately 6- and approximately 4-fold activation of enzyme activity was observed in LPLHL-(85-91) and LPLHLD, respectively. In summary, our results have identified 11 amino acid residues in the N-terminal domain of LPL (residues 65-68 and 73-79) that appear to act cooperatively to enable substantial activation of human LPL by apoC-II.
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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 | 0.000 |
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".