Ribulose bisphosphate carboxylase small subunit (cbbS) is a 110-residue protein from Halothiobacillus neapolitanus (strain ATCC 23641 / c2). This is its AlphaFold structure prediction, created 1 Aug 2025. UniProt accession: P45686.
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The mean pLDDT of this model is 95.9 (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 | 90% |
| 70 to 90 | Confident: backbone generally right | 9% |
| 50 to 70 | Low: treat with caution | 1% |
| Below 50 | Very low: often disordered regions | 0% |
What pLDDT means and how to read it
RuBisCO catalyzes two reactions: the carboxylation of D-ribulose 1,5-bisphosphate, the primary event in carbon dioxide fixation, as well as the oxidative fragmentation of the pentose substrate. Both reactions occur simultaneously and in competition at the same active site (PubMed:18258595, PubMed:18974784, Ref.3). There are estimated to be 270 RuBisCO heterohexadecamers per carboxysome (Ref.6)
Heterohexadecamer of 8 large and 8 small subunits (PubMed:32123388). Interacts with CsoS2 (PubMed:30305640). Forms a CsoS2-CsoS1-RuBisCO complex (Probable). Holo-RuBisCO interacts with the N-terminal repeats of CsoS2; binding is sensitive to ionic strength. A fusion of a single N-terminal repeat to the C-terminus of the large subunit of RuBisCO (cbbL) shows the repeat can lie between a CbbL…
Carboxysome
Compare the prediction with experimentally determined structures of the same protein:
| PDB ID | Method | Resolution | Chains and residues |
|---|---|---|---|
| 1SVD | X-ray | 1.8 Å | M=1-110 |
| 7SMK | EM | 1.98 Å | B=1-110 |
| 7SNV | EM | 2.07 Å | B=1-110 |
| 6UEW | X-ray | 2.4 Å | B/D/F/H=1-110 |
| 7ZBT | EM | 3.3 Å | I/J/K/L/M/N/O/P=1-110 |
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