Specificity of Staphyloferrin B Recognition by the SirA Receptor from Staphylococcus aureus
Why this work is in the frame
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Bibliographic record
Abstract
Many organisms use sophisticated systems to acquire growth-limiting iron. Iron limitation is especially apparent in bacterial pathogens of mammalian hosts where free iron concentrations are physiologically negligible. A common strategy is to secrete low molecular weight iron chelators, termed siderophores, and express high affinity receptors for the siderophore-iron complex. Staphylococcus aureus, a widespread pathogen, produces two siderophores, staphyloferrin A (SA) and staphyloferrin B (SB). We have determined the crystal structure of the staphyloferrin B receptor, SirA, at high resolution in both the apo and Fe(III)-SB (FeSB)-bound forms. SirA, a member of the class III binding protein family of metal receptors, has N- and C-terminal domains, each composed of mainly a β-stranded core and α-helical periphery. The domains are bridged by a single α-helix and together form the FeSB binding site. SB coordinates Fe(III) through five oxygen atoms and one nitrogen atom in distorted octahedral geometry. SirA undergoes conformational change upon siderophore binding, largely securing two loops from the C-terminal domain to enclose FeSB with a low nanomolar dissociation constant. The staphyloferrin A receptor, HtsA, homologous to SirA, also encloses its cognate siderophore (FeSA); however, the largest conformational rearrangements involve a different region of the C-terminal domain. FeSB is uniquely situated in the binding pocket of SirA with few of the contacting residues being conserved with those of HtsA interacting with FeSA. Although both SirA and HtsA bind siderophores from the same α-hydroxycarboxylate class, the unique structural features of each receptor provides an explanation for their distinct specificity.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it