Cryo-EM reveals how Staphylococcus aureus extracts hemin from hemoglobin-haptoglobin complex
Researchers used cryo-electron microscopy to determine how the bacterium Staphylococcus aureus uses its IsdH receptor to extract hemin (an iron-containing compound) from the hemoglobin-haptoglobin complex in human blood. The IsdH receptor uses distinct domains to anchor to hemoglobin and extract hemin, with the process involving dynamic molecular motions that destabilize the hemoglobin structure. This finding explains a bacterial mechanism for acquiring iron from host blood and evading immune clearance, with potential implications for understanding S. aureus pathogenesis.
Using cryo-electron microscopy at 3.1 Ångstrom resolution, researchers determined the structural mechanism by which Staphylococcus aureus IsdH receptor extracts hemin from the hemoglobin-haptoglobin (Hb:Hp) complex, the major circulating form of hemoglobin outside red blood cells. The IsdH receptor contains multiple domains: an N-terminal NEAT domain (N1) that anchors to hemoglobin, and downstream N2N3 domains that function as an extraction unit targeting beta-hemoglobin. Notably, N-linked glycans on haptoglobin sterically influence which hemoglobin molecule the extraction unit engages, demonstrating how the complex's structure affects bacterial access. Kinetic assays and three-dimensional variability analysis revealed that IsdH actively accelerates hemin release through dynamic receptor motions that transiently perturb the hemoglobin F-helix. The structural alignment with macrophage CD163 receptors suggests that IsdH may simultaneously disrupt immune recognition and clearance of the Hb:Hp complex, revealing how this pathogen coordinates iron acquisition with immune evasion.
What's missing
The study does not discuss potential therapeutic applications or whether IsdH could serve as a drug target for treating S. aureus infections. Additionally, the functional significance of the dynamic motions identified through variability analysis and their quantitative contribution to hemin extraction efficiency could be further explored.
What different sources said
- bioRxivCenter
Cryo-EM provides insight into how the Staphylococcus aureus IsdH receptor removes hemin from the hemoglobin:haptoglobin complex
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