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Energetics underlying hemin extraction from human hemoglobin by Staphylococcus aureus

Citation

Sjodt, M and Macdonald, R and Marshall, JD and Clayton, J and Olson, JS and Phillips, M and Gell, DA and Wereszczynski, J and Clubb, RT, Energetics underlying hemin extraction from human hemoglobin by Staphylococcus aureus, Journal of Biological Chemistry, 293, (18) pp. 6942-6957. ISSN 0021-9258 (2018) [Refereed Article]


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DOI: doi:10.1074/jbc.RA117.000803

Abstract

Staphylococcus aureus is a leading cause of life-threatening infections in the United States. It actively acquires the essential nutrient iron from human hemoglobin (Hb) using the iron-regulated surface-determinant (Isd) system. This process is initiated when the closely related bacterial IsdB and IsdH receptors bind to Hb and extract its hemin through a conserved tri-domain unit that contains two NEAr iron Transporter (NEAT) domains that are connected by a helical linker domain. Previously, we demonstrated that the tri-domain unit within IsdH (IsdHN2N3) triggers hemin release by distorting Hbs F-helix. Here, we report that IsdHN2N3 promotes hemin release from both the - and -subunits. Using a receptor mutant that only binds to the -subunit of Hb and a stopped-flow transfer assay, we determined the energetics and micro-rate constants of hemin extraction from tetrameric Hb. We found that at 37 C, the receptor accelerates hemin release from Hb up to 13,400- fold, with an activation enthalpy of 19.5 ± 1.1 kcal/mol. We propose that hemin removal requires the rate-limiting hydrolytic cleavage of the axial HisF8 N±Fe3± bond, which, based on molecular dynamics simulations, may be facilitated by receptor-induced bond hydration. Isothermal titration calorimetry experiments revealed that two distinct IsdHN2N3-Hb proteinprotein interfaces promote hemin release. A high-affinity receptorHb(A-helix) interface contributed -95% of the total binding standard free energy, enabling much weaker receptor interactions with Hbs F-helix that distort its hemin pocket and cause unfavorable changes in the binding enthalpy. We present a model indicating that receptor-introduced structural distortions and increased solvation underlie the IsdH-mediated hemin extraction mechanism.

Item Details

Item Type:Refereed Article
Keywords:haemoglobin, staphylococcus aureus
Research Division:Biological Sciences
Research Group:Biochemistry and Cell Biology
Research Field:Structural Biology (incl. Macromolecular Modelling)
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Biological Sciences
Author:Gell, DA (Dr David Gell)
ID Code:128723
Year Published:2018
Deposited By:Medicine (Discipline)
Deposited On:2018-10-10
Last Modified:2018-10-10
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