The Staphylococcus aureus IsdH Receptor Forms a Dynamic Complex with Human Hemoglobin that Triggers Heme Release via Two Distinct Hot Spots

JOURNAL OF MOLECULAR BIOLOGY

卷:432

Article

Ellis-Guardiola, Ken^1,2  Clayton, Joseph^4,5  Pham, Clarissa^1,2  Mahoney, Brendan J.^1,2  Wereszczynski, Jeff^4,5  Clubb, Robert T.^1,2,3 

[1] Univ Calif Los Angeles, Dept Chem & Biochem, 611 Charles Young Dr East, Los Angeles, CA 90095 USA

[2] Univ Calif Los Angeles, DOE Inst Genom & Proteom, 611 Charles Young Dr East, Los Angeles, CA 90095 USA

[3] Univ Calif Los Angeles, Inst Mol Biol, 611 Charles Young Dr East, Los Angeles, CA 90095 USA

[4] IIT, Dept Phys, Univ Technol Pk,3440 South Dearborn St,Suite 150, Chicago, IL 60616 USA

[5] IIT, Ctr Mol Study Condensed Soft Matter, Univ Technol Pk,3440 South Dearborn St,Suite 150, Chicago, IL 60616 USA

关键词: Iron-regulated surface determinant system;    Staphylococcus aureus hemoglobin receptor;    Stopped-flow spectrophotometry;    Molecular dynamics;    Nuclear magnetic resonance spectroscopy;   

DOI  :  10.1016/j.jmb.2019.12.023

来源: Elsevier

【 摘 要 】

Iron is an essential nutrient that is actively acquired by bacterial pathogens during infections. Clinically important Staphylococcus aureus obtains iron by extracting heme from hemoglobin (Hb) using the closely related IsdB and IsdH surface receptors. In IsdH, extraction is mediated by a conserved tridomain unit that contains its second (N2) and third (N3) NEAT domains joined by a helical linker, called IsdH(N2N3). Leveraging the crystal structure of the IsdH(N2N3):Hb complex, we have probed the mechanism of heme capture using NMR, stopped-flow transfer kinetics measurements, and molecular dynamics (MD) simulations. NMR studies of the 220 kDa IsdH(N2N3):Hb complex reveal that it is dynamic, with persistent interdomain motions enabling the linker and N3 domains in the receptor to transiently engage Hb to remove its heme. An alanine mutagenesis analysis reveals that two receptor subsites positioned similar to 20 angstrom apart trigger heme release by contacting Hb's F-helix. These subsites are located within the N3 and linker domains and appear to play distinct roles in stabilizing the heme transfer transition state. Linker domain contacts primarily function to destabilize Hb-heme interactions, thereby lowering Delta H double dagger, while contacts from the N3 subsite play a similar destabilizing role, but also form a bridge through which heme moves from Hb to the receptor. Interestingly, MD simulations suggest that within the transiently forming interface, both the F-helix and receptor bridge are in motion, dynamically sampling conformations that are suitable for heme transfer. Thus, IsdH triggers heme release from Hb via a flexible, low-affinity interface that forms fleetingly in solution. (C) 2019 Published by Elsevier Ltd.

【 授权许可】

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