3qzn
Staphylococcus aureus IsdA NEAT domain Y166A variant in complex with heme
Structural highlights
FunctionISDA_STAAN Transfers its hemin to hemin-free IsdC (apo-IsdC) directly probably through the activated holo-IsdA-apo-IsdC complex and driven by the higher affinity of apo-IsdC for the cofactor. The reaction is reversible. Binds transferrin, lactoferrin, heme, hemoglobin, hemin, fetuin, asialofetuin and protein A. Also binds fibronectin and chains B-beta and gamma of fibrinogen. Could play a role in the removal of heme from hemoglobin. The IsdA-mediated iron-acquisition system from transferrin could play only an ancillary role in the iron uptake whereas the siderophore-mediated iron-acquisition system from transferrin seems to play an essential or dominant role. May function as a reservoir for heme. Involved in adherence of S.aureus to human desquamated nasal epithelial cells and is required for nasal colonization. Protects S.aureus against the bactericidal protease activity of apolactoferrin in vitro and confers resistance to bovine lactoferricin. Also IsdA and/or IsdB promote resistance to hydrogen peroxide and killing by neutrophils (By similarity). Publication Abstract from PubMedIn humans, heme iron is the most abundant iron source, and bacterial pathogens such as Staphylococcus aureus acquire it for growth. IsdB of S. aureus acquires Fe(III)-protoporphyrin IX (heme) from hemoglobin for transfer to IsdC via IsdA. These three cell-wall-anchored Isd (iron-regulated surface determinant) proteins contain conserved NEAT (near iron transport) domains. The purpose of this work was to delineate the mechanism of heme binding and transfer between the NEAT domains of IsdA, IsdB, and IsdC using a combination of structural and spectroscopic studies. X-ray crystal structures of IsdA NEAT domain (IsdA-N1) variants reveal that removing the native heme-iron ligand Tyr166 is compensated for by iron coordination by His83 on the distal side and that no single mutation of distal loop residues is sufficient to perturb the IsdA-heme complex. Also, alternate heme-iron coordination was observed in structures of IsdA-N1 bound to reduced Fe(II)-protoporphyrin IX and Co(III)-protoporphyrin IX. The IsdA-N1 structural data were correlated with heme transfer kinetics from the NEAT domains of IsdB and IsdC. We demonstrated that the NEAT domains transfer heme at rates comparable to full-length proteins. The second-order rate constant for heme transfer from IsdA-N1 was modestly affected (<2-fold) by the IsdA variants, excluding those at Tyr166. Substituting Tyr166 with Ala or Phe changed the reaction mechanism to one with two observable steps and decreased observed rates >15-fold (to 100-fold excess IsdC). We propose a heme transfer model wherein NEAT domain complexes pass heme iron directly from an iron-coordinating Tyr of the donor protein to the homologous Tyr residues of the acceptor protein. Iron-Coordinating Tyrosine Is a Key Determinant of NEAT Domain Heme Transfer.,Grigg JC, Mao CX, Murphy ME J Mol Biol. 2011 Aug 26. PMID:21893067[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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