Phosphatidylserine Synthase-1 and -2 Are Localized to Mitochondria-associated Membranes
Why this work is in the frame
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Bibliographic record
Abstract
We report the subcellular localization of enzymes involved in phosphatidylserine biosynthesis in mammalian cells. Several lines of evidence suggest that phosphatidylserine synthase-1 (PSS1) is highly enriched in mitochondria-associated membranes (MAM) and is largely excluded from the bulk of the endoplasmic reticulum (ER). Taking advantage of the substrate specificity of PSS1, we showed that (i) MAM contain choline exchange activity, whereas this activity is very low in the bulk of the ER, (ii) serine exchange activity is inhibited by choline to a much greater extent in MAM than in ER, and (iii) MAM use phosphatidylcholine and phosphatidylethanolamine as substrates for phosphatidylserine biosynthesis, whereas the ER utilizes only phosphatidylethanolamine. According to immunoblotting of proteins from both CHO-K1 cells and murine liver, PSS1 is localized to MAM, and in hepatoma cells stably expressing PSS1 this protein is highly enriched in MAM. Since the ER contains serine and ethanolamine exchange activities, we had predicted that PSS2 would account for the serine exchange activity in the ER. Unexpectedly, using immunoblotting experiments, we found that (i) PSS2 of CHO-K1 cells is present only in MAM and (ii) PSS2 is restricted to MAM of McArdle cells expressing recombinant PSS2. These data leave open the question of which enzyme imparts PSS activity to the ER and suggest that a third isoform of PSS might be located in the ER.
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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 | 0.002 |
| 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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 it