Regulatory Monoubiquitination of Phosphoenolpyruvate Carboxylase in Germinating Castor Oil Seeds
Bibliographic record
Abstract
Phosphoenolpyruvate carboxylase (PEPC) is a tightly regulated enzyme situated at the core of plant C-metabolism. Although its anaplerotic role and control by allosteric effectors, reversible phosphorylation, and oligomerization have been well documented in the endosperm of developing castor oil seeds (COS), relatively little is known about PEPC in germinating COS. The initial phase of COS germination was accompanied by elevated PEPC activity and accumulation of comparable amounts of pre-existing 107-kDa and inducible 110-kDa immunoreactive PEPC polypeptides (p107 and p110, respectively). A 440-kDa PEPC heterotetramer composed of an equivalent ratio of non-phosphorylated p110 and p107 subunits was purified from germinated COS. N-terminal microsequencing, mass spectrometry, and immunoblotting revealed that both subunits arose from the same gene (RcPpc3) that encodes the p107 subunit of a phosphorylated 410-kDa PEPC homotetramer in developing COS but that p110 is a monoubiquitinated form of p107. Tandem mass spectrometry sequencing of a diglycinated tryptic peptide identified Lys-628 as p110's monoubiquitination site. This residue is conserved in vascular plant PEPCs and is proximal to a PEP-binding/catalytic domain. Incubation with a human deubiquitinating enzyme (USP-2 core) converted the p110:p107 PEPC heterotetramer into a p107 homotetramer while significantly reducing the enzyme's K(m)(PEP) and sensitivity to allosteric activators (hexose-Ps, glycerol-3-P) and inhibitors (malate, aspartate). Monoubiquitination is a non-destructive and reversible post-translational modification involved in the control of diverse processes such as transcription, endocytosis, and signal transduction. The current study demonstrates that tissue-specific monoubiquitination of a metabolic enzyme can also occur and that this modification influences its kinetic and regulatory properties.
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How this classification was reachedexpand
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 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".