title: Functionally distinct NEAT (NEAr Transporter) domains within the Staphylococcus aureus IsdH/HarA protein extract heme from methemoglobin.
abstract: The pathogen Staphylococcus aureus uses iron-regulated surface determinant (Isd) proteins to scavenge the essential nutrient iron from host hemoproteins. The IsdH protein (also known as HarA) is a receptor for hemoglobin (Hb), haptoglobin (Hp), and the Hb-Hp complex. It contains three NEAT (NEAr Transporter) domains: IsdH(N1), IsdH(N2), and IsdH(N3). Here we show that they have different functions; IsdH(N1) binds Hb and Hp, whereas IsdH(N3) captures heme that is released from Hb. The staphylococcal IsdB protein also functions as an Hb receptor. Primary sequence homology to IsdH indicates that it will also employ functionally distinct NEAT domains to bind heme and Hb. We have used site-directed mutagenesis and surface plasmon resonance methods to localize the Hp and Hb binding surface on IsdH(N1). High affinity binding to these structurally unrelated proteins requires residues located within a conserved aromatic motif that is positioned at the end of the beta-barrel structure. Interestingly, this site is quite malleable, as other NEAT domains use it to bind heme. We also demonstrate that the IsdC NEAT domain can capture heme directly from Hb, suggesting that there are multiple pathways for heme transfer across the cell wall.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics, UCLA, Los Angeles, California 90095, USA.
authors.forename: Rosemarie M
authors.initials: RM
authors.lastname: Pilpa
authors.forename: Scott A
authors.initials: SA
authors.lastname: Robson
authors.forename: Valerie A
authors.initials: VA
authors.lastname: Villareal
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Wong
authors.forename: Martin
authors.initials: M
authors.lastname: Phillips
authors.forename: Robert T
authors.initials: RT
authors.lastname: Clubb
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000302:isolation & purification / Q000378:metabolism*; D008706:Methemoglobin / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013211:Staphylococcus aureus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D002352:Carrier Proteins; C488727:IsdC protein, Staphylococcus aureus; C512792:IsdH protein, Staphylococcus aureus; D011956:Receptors, Cell Surface; D006418:Heme; D008706:Methemoglobin