Directed Inter-domain Motions Enable the IsdH Staphylococcus aureus Receptor to Rapidly Extract Heme from Human Hemoglobin

• Published in: Journal of molecular biology 2022-06, Vol.434 (12), p.167623-167623, Article 167623
• Main Authors: Clayton, Joseph, Ellis-Guardiola, Kat, Mahoney, Brendan J., Soule, Jess, Liu, William, Clubb, Robert T., Wereszczynski, Jeff
• Format: Article
• Language: English
• Subjects: Antigens, Bacterial - chemistry; Antigens, Bacterial - genetics; Heme - chemistry; hemoglobin receptor; Hemoglobins - chemistry; Humans; iron-regulated surface determinant system; molecular dynamics; Molecular Dynamics Simulation; Motion; Protein Domains; Receptors, Cell Surface - chemistry; Receptors, Cell Surface - genetics; Staphylococcal Infections - microbiology; Staphylococcus aureus; Staphylococcus aureus - pathogenicity; stopped-flow spectrophotometry
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2022.167623

[Display omitted] •S. aureus receptor IsdH actively extracts heme from human hemoglobin.•Molecular simulations, Markov modeling, and kinetic measurements show directed inter-domain motions drive heme extraction.•A short, flexible inter-domain tether controls the directionality of the N3 domain and, in turn, the rate of heme extraction.•Our results show an unstructured sequence connecting domains controls the directionality and magnitude of important motions. Pathogenic Staphylococcus aureus actively acquires iron from human hemoglobin (Hb) using the IsdH surface receptor. Heme extraction is mediated by a tri-domain unit within the receptor that contains its second (N2) and third (N3) NEAT domains joined by a helical linker domain. Extraction occurs within a dynamic complex, in which receptors engage each globin chain; the N2 domain tightly binds to Hb, while substantial inter-domain motions within the receptor enable its N3 domain to transiently distort the globin’s heme pocket. Using molecular simulations coupled with Markov modeling, along with stopped-flow experiments to quantitatively measure heme transfer kinetics, we show that directed inter-domain motions within the receptor play a critical role in the extraction process. The directionality of N3 domain motion and the rate of heme extraction is controlled by amino acids within a short, flexible inter-domain tether that connects the N2 and linker domains. In the wild-type receptor directed motions originating from the tether enable the N3 domain to populate configurations capable of distorting Hb’s pocket, whereas mutant receptors containing altered tethers are less able to adopt these conformers and capture heme slowly via indirect processes in which Hb first releases heme into the solvent. Thus, our results show inter-domain motions within the IsdH receptor play a critical role in its ability to extract heme from Hb and highlight the importance of directed motions by the short, unstructured, amino acid sequence connecting the domains in controlling the directionality and magnitude of these functionally important motions.