Complement C1s subcomponent (C1S) is a 688-residue protein from Homo sapiens. This is its AlphaFold structure prediction, created 1 Aug 2025. UniProt accession: P09871.
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The mean pLDDT of this model is 87.9 (confident 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 | 66% |
| 70 to 90 | Confident: backbone generally right | 25% |
| 50 to 70 | Low: treat with caution | 6% |
| Below 50 | Very low: often disordered regions | 2% |
What pLDDT means and how to read it
Component of the complement C1 complex, a multiprotein complex that initiates the classical pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:11445589, PubMed:16169853, PubMed:417728, PubMed:467643, PubMed:6271784, PubMed:6282646, PubMed:6319179, PubMed:70787, PubMed:9422791). C1S is activated following association of the C1 complex with immunoglobulins (IgG or IgM) complexed with antigens to form antigen-antibody complexes on the surface of pathogens (PubMed:34155115). C1S is cleaved and activated by C1R to generate C1s subcomponent heavy and light chains…
Core component of the complement C1 complex, a calcium-dependent complex composed of 1 molecule of the C1Q subcomplex, 2 molecules of C1R and 2 molecules of C1S (PubMed:19473974, PubMed:2007122, PubMed:28104818, PubMed:29311313, PubMed:2988513, PubMed:2989825, PubMed:34155115, PubMed:6952210). The C1Q subcomplex is composed 18 subunits: 3 chains of C1QA, C1QB, and C1QC trimerize to form 6…
Secreted, Cell surface
Compare the prediction with experimentally determined structures of the same protein:
| PDB ID | Method | Resolution | Chains and residues |
|---|---|---|---|
| 1NZI | X-ray | 1.5 Å | A/B=16-174 |
| 1ELV | X-ray | 1.7 Å | A=358-688 |
| 8TYP | X-ray | 1.8 Å | A=358-688 |
| 4LOS | X-ray | 2.0 Å | A=172-358 |
| 4LOR | X-ray | 2.5 Å | A=17-292 |
| 5UBM | X-ray | 2.5 Å | A=437-688, B=285-436 |
| 8GMN | X-ray | 2.6 Å | A/B/C/D=358-688 |
| 9X1H | EM | 2.6 Å | A/B=16-292 |
| 4J1Y | X-ray | 2.66 Å | A/B=292-688 |
| 4LMF | X-ray | 2.92 Å | A/B/C/D=17-292 |
| 4LOT | X-ray | 2.92 Å | A=175-423 |
| 8W18 | X-ray | 3.94 Å | A=292-437, B=438-688 |
| 6F1C | X-ray | 4.2 Å | B/D=16-292 |
| 6F1H | X-ray | 4.5 Å | B/D=17-292 |
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