Characterization of a Synaptic Vesicle Binding Motif on the Distal CaV2.2 Channel C-terminal
Bibliographic record
Abstract
Neurotransmitter is released from synaptic vesicles (SVs) that are gated to fuse with the presynaptic membrane by calcium ions that enter through voltage-gated calcium channels (CaVs). There is compelling evidence that SVs associate closely with the CaVs but the molecular linking mechanisms remain poorly understood. Using a cell-free, synaptic vesicle-pull-down assay method (SV-PD) we have recently demonstrated that SVs can bind both to the intact CaV2.2 channel and also to a fusion protein comprising the distal third, C3 segment, of its long C-terminal. This site was localized to a 49 amino acid region just proximal to the C-terminal tip. To further restrict the SV binding site we generated five, 10 amino acid mimetic blocking peptides spanning this region. Of these, HQARRVPNGY effectively inhibited SV-PD and also inhibited SV recycling when cryoloaded into chick brain nerve terminals (synaptosomes). Further, SV-PD was markedly reduced using a C3 fusion protein that lacked the HQARRVPNGY sequence, C3HQless. We zeroed in on the SV binding motif within HQARRVPNGY by means of a palette of mutant blocking peptides. To our surprise, peptides that lacked the highly conserved VPNGY sequence still blocked SV-PD. However, substitution of the HQ and RR amino acids markedly reduced block. Of these, the RR pair was essential but not sufficient as the full block was not observed without H suggesting a CaV2.2 SV binding motif of HxxRR. Interestingly, CaV2.1, the other primary presynaptic calcium channel, exhibits a similar motif, RHxRR, that likely serves the same function. Bioinformatic analysis showed that variations of this binding motif, +(+) xRR (where + is a positively charged aa H or R), are conserved from lung-fish to man. Further studies will be necessary to identify the C terminal motif binding partner on the SV itself and to determine the role of this molecular interaction in synaptic transmission. We hypothesize that the distal C-terminal participates in the capture of the SVs from the cytoplasm, initiating their delivery to the active zone where additional tethering interactions secure the vesicle within range of the CaV single Ca(2+) domains.
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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".