Interaction of human complement with Sbi, a staphylococcal immunoglobulin-binding protein: indications of a novel mechanism of complement evasion by Staphylococcus aureus.
Bibliographic record
Abstract
Staphylococcal immunoglobulin-binding protein, Sbi, is a 436-residue protein produced by many strains of Staphylococcus aureus.It was previously characterized as being cell surface-associated and having binding capacity for human IgG and β 2 -glycoprotein I.Here we show using small angle x-ray scattering that the proposed extracellular region of Sbi (Sbi-E) is an elongated molecule consisting of four globular domains, two immunoglobulin-binding domains (I and II) and two novel domains (III and IV).We further show that together domains III and IV (Sbi-III-IV), as well as domain IV on its own (Sbi-IV), bind complement component C3 via contacts involving both the C3dg fragment and the C3a anaphylatoxin domain.Preincubation of human serum with either Sbi-E or Sbi-III-IV is inhibitory to all complement pathways, whereas domain IV specifically inhibits the alternative pathway.Monitoring C3 activation in serum incubated with Sbi fragments reveals that Sbi-E and Sbi-III-IV both activate the alternative pathway, leading to consumption of C3.By contrast, inhibition of this pathway by Sbi-IV does not involve C3 consumption.The observation that Sbi-E activates the alternative pathway is counterintuitive to intact Sbi being cell wall-associated, as recruiting complement to the surface of S. aureus would be deleterious to the bacterium.Upon re-examination of this issue, we found that Sbi was not associated with the cell wall fraction, but rather was found in the growth medium, consistent with
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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 | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".