The IsdC protein from Staphylococcus aureus uses a flexible binding pocket to capture heme.
Staphylococcus aureus scavenges heme-iron from host hemoproteins using iron-regulated surface determinant (Isd) proteins. IsdC is the central conduit through which heme is passed across the cell wall and binds this molecule using a NEAr Transporter (NEAT) domain. NMR spectroscopy was used to determine the structure of IsdC in complex with a heme analog, zinc-substituted protoporphyrin IX (ZnPPIX). The backbone coordinates of the ensemble of conformers representing the structure exhibit a root mean square deviation to the mean structure of 0.53 +/- 0.11 angstroms. IsdC partially buries protoporphyrin within a large hydrophobic pocket that is located at the end of its beta-barrel structure. The central metal ion of the analog adopts a pentacoordinate geometry in which a highly conserved tyrosine residue serves as a proximal ligand. Consistent with the structure and its role in heme transfer across the cell wall, we show that IsdC weakly binds heme (K(D) = 0.34 +/- 0.12 microm) and that ZnPPIX rapidly dissociates from the protein at a rate of 126 +/- 30 s(-1). NMR studies of the apo-form of IsdC reveal that a 3(10) helix within the binding pocket undergoes a flexible to rigid transition as heme is captured. This structural plasticity may increase the efficiency of heme transfer across the cell wall by facilitating protein-protein interactions between apoIsdC and upstream hemoproteins.
Villareal
Valerie A
VA
Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, California 90095, USA.
Pilpa
Rosemarie M
RM
Robson
Scott A
SA
Fadeev
Evgeny A
EA
Clubb
Robert T
RT
D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006418:Heme / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011524:Protoporphyrins / Q000737:chemistry / Q000378:metabolism; D013211:Staphylococcus aureus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
D001059:Apoproteins; D002352:Carrier Proteins; C488727:IsdC protein, Staphylococcus aureus; D011524:Protoporphyrins; D006418:Heme; C028025:protoporphyrin IX; D015032:Zinc