Immunoglobulin G-binding protein A (spa) is a 450-residue protein from Staphylococcus aureus (strain Mu50 / ATCC 700699). This is its AlphaFold structure prediction, created 1 Aug 2025. UniProt accession: P0A015.
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The mean pLDDT of this model is 68.1 (low 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 | 39% |
| 70 to 90 | Confident: backbone generally right | 18% |
| 50 to 70 | Low: treat with caution | 6% |
| Below 50 | Very low: often disordered regions | 37% |
What pLDDT means and how to read it
Plays a role in the inhibition of the host innate and adaptive immune responses. Possesses five immunoglobulin-binding domains that capture both the fragment crystallizable region (Fc region) and the Fab region (part of Ig that identifies antigen) of immunoglobulins (By similarity). In turn, Staphylococcus aureus is protected from phagocytic killing via inhibition of Ig Fc region. In addition, the host elicited B-cell response is prevented due to a decrease of antibody-secreting cell proliferation that enter the bone marrow, thereby decreasing long-term antibody production. Inhibits osteogenesis by preventing osteoblast proliferation and expression of alkaline phosphatase, type I collagen,…
Interacts with host TNFRSF1A; this interaction leads to the stimulation of both surface expression and shedding of TNFRSF1A. Interacts (via B domain) with IgG1, IgG2 and IgG4; spa interferes with IgG oligomerization and IgG:C1 complement complex formation, preventing complement activation and ultimately protecting bacteria from phagocytic killing
Secreted, cell wall
Compare the prediction with experimentally determined structures of the same protein:
| PDB ID | Method | Resolution | Chains and residues |
|---|---|---|---|
| 4IOI | X-ray | 1.95 Å | H=101-151 |
| 4HJG | X-ray | 2.0 Å | H=101-151 |
| 4HKZ | X-ray | 2.08 Å | H=101-151 |
| 8JXS | EM | 3.0 Å | C=120-151 |
| 8JXR | EM | 3.57 Å | C=121-151 |
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