Localization and targeting of B2-1, a guanine-nucleotide exchange factor for ADP-ribosylation factors.
Bibliographic record
Abstract
B2-1 (cytohesin-1) is a member of a group of proteins (including ARNO and ARNO3) that are all of similar size and domain composition. The three proteins contain an N-terminal coiled-coil domain, followed by Sec7 and pleckstrin homology (PH) domains. Recently, several research groups have shown that B2-1 has varied cellular functions and subcellular locations. One of these is an association of the B2-1 Sec7 domain with the plasma membrane, binding to the cytoplasmic portion of the integrin P2 chain (CD 18) and a postulated involvement in inside-out signaling. Other groups have shown that B2-1 and the related proteins are guanine nucleotide-exchange factors that act upon ADP ribosylation factors (ARFs) and are localized to the Golgi or plasma membrane. Here we report the subcellular localization of B2-1 protein. Interestingly, B2-1 does not localize to the plasma membrane, but rather associates with a distinct Golgi complex compartment. B2-1's distribution was disrupted by brefeldin A, a drug that rapidly disrupts the Golgi apparatus by inhibiting ARF activity. Transient transfection of GFP-tagged B2-1 showed Golgi complex targeting. Excessive overexpression of transfected B2-1 also caused partial Golgi dispersion. While it is well established that the Sec7 domain has GEF activity and the PH domain anchors the proteins to membrane phosphoinositols, the function of the N-terminal coiled-coil region is unknown. Here it was shown that B2-1's N-terminus (residues 1--54) is necessary and sufficient to target the protein to the Golgi. The Sec7+PH domains of B2-1 (residues 55--398) were not sufficient for Golgi localization. Further deletion analysis and point mutagenesis indicated that the coiled-coil domain within the N terminus is responsible for Golgi targeting. Furthermore, ARNO and ARNO3 N termini also have the same capability for targeting to the Golgi. It was concluded that the N-terminal a-helical coiled-coil domain is used to target this family of proteins to the Golgi complex.
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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".