Small COPII coat GTPase SAR1 (SAR1) is a 190-residue protein from Saccharomyces cerevisiae (strain ATCC 204508 / S288c). This is its AlphaFold structure prediction, created 1 Aug 2025. UniProt accession: P20606.
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The mean pLDDT of this model is 90.8 (very high overall). pLDDT is AlphaFold's per-residue confidence score from 0 to 100. In MolViewer, choose the B-factor color scheme to color the model by pLDDT, because AlphaFold stores it in the B-factor column.
| pLDDT band | Meaning | Share of residues |
|---|---|---|
| Above 90 | Very high: backbone and side chains are usually accurate | 75% |
| 70 to 90 | Confident: backbone generally right | 15% |
| 50 to 70 | Low: treat with caution | 10% |
| Below 50 | Very low: often disordered regions | 1% |
What pLDDT means and how to read it
Small GTPase component of the coat protein complex II (COPII) which promotes the formation of transport vesicles from the endoplasmic reticulum (ER). The coat has two main functions, the physical deformation of the endoplasmic reticulum membrane into vesicles and the selection of cargo molecules. SAR1 controls the coat assembly in a stepwise manner. Activated SAR1-GTP by SEC12 binds to membranes first and recruits the SEC23/24 complex. These SEC23/24-SAR1 prebudding intermediates are then collected by the SEC13/31 complex as subunits polymerize to form coated transport vesicles. Conversion to SAR1-GDP triggers coat release and recycles COPII subunits
COPII is composed of at least 5 proteins: the SEC23/24 complex, the SEC13/31 complex and SAR1. Interacts with EMP24
Cytoplasmic vesicle, COPII-coated vesicle membrane, Endoplasmic reticulum membrane, Golgi apparatus membrane
Compare the prediction with experimentally determined structures of the same protein:
| PDB ID | Method | Resolution | Chains and residues |
|---|---|---|---|
| 6X90 | X-ray | 2.26 Å | A=24-190 |
| 1M2O | X-ray | 2.5 Å | B/D=1-190 |
| 2QTV | X-ray | 2.5 Å | B=23-189 |
| 8BSH | EM | 3.8 Å | B=1-190 |
| 6ZGA | EM | 4.6 Å | C=1-190, G=1-189 |
| 6GNI | EM | 4.9 Å | B=23-189 |
| 4BZI | EM | 23.0 Å | B/J/K=1-190 |
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