Septin 2 phosphorylation: theoretical and mass spectrometric evidence for the existence of a single phosphorylation site <i>in vivo</i>
Bibliographic record
Abstract
Septins constitute a family of conserved proteins that are required for cytokinesis in a wide range of organisms. Most cells express a set of septin proteins and these are found to assemble into hetero-oligomeric septin complexes that appear filamentous. However, the mechanisms controlling the function and polymerization of septins are not known. We therefore examined the possibility that septins could be post-translationally modified by phosphorylation. We present herein a combined theoretical and experimental approach for the analysis of Septin 2 (Sept2) monophosphorylation in vivo. We purified and characterized the human recombinant Sept2, a 45-kDa protein, expressed from Sf21 insect cells. Analysis by matrix-assisted laser desorption/ionization quadrupole time-of-flight mass spectrometry on the full-length protein sequence of wild-type Sept2 revealed a unique phosphorylation site at residue Ser248 in vivo, which is consistent with one of the twelve phosphorylation sites in the protein sequence theoretically predicted by the Netphos program. Additional predictions with the motif scan programs Scansite and Prosite suggest that the phosphorylation of wild-type Sept2 might be a potential substrate for casein kinase 2. Site-directed mutagenesis of residue 248 from serine to alanine abrogated this phosphorylation. The location of phosphorylation in Sept2 differs from the sites predicted for cGMP-dependent protein kinase (PKG) phosphorylation in Septin 3, raising the possibility that different septins may undergo distinct phosphorylation events that could control their functions in important cellular processes such as neurotransmission or cytokinesis.
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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".