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Detzel MS, Schmalohr BF, Steinbock F, Hopp MT, Ramoji A, Paul George AA, Neugebauer U, Imhof D. Revisiting the interaction of heme with hemopexin. Biol Chem 2021; 402:675-691. [PMID: 33581700 DOI: 10.1515/hsz-2020-0347] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 02/06/2021] [Indexed: 12/23/2022]
Abstract
In hemolytic disorders, erythrocyte lysis results in massive release of hemoglobin and, subsequently, toxic heme. Hemopexin is the major protective factor against heme toxicity in human blood and currently considered for therapeutic use. It has been widely accepted that hemopexin binds heme with extraordinarily high affinity of <1 pM in a 1:1 ratio. However, several lines of evidence point to a higher stoichiometry and lower affinity than determined 50 years ago. Here, we re-analyzed these data. SPR and UV/Vis spectroscopy were used to monitor the interaction of heme with the human protein. The heme-binding sites of hemopexin were characterized using hemopexin-derived peptide models and competitive displacement assays. We obtained a K D value of 0.32 ± 0.04 nM and the ratio for the interaction was determined to be 1:1 at low heme concentrations and at least 2:1 (heme:hemopexin) at high concentrations. We were able to identify two yet unknown potential heme-binding sites on hemopexin. Furthermore, molecular modelling with a newly created homology model of human hemopexin suggested a possible recruiting mechanism by which heme could consecutively bind several histidine residues on its way into the binding pocket. Our findings have direct implications for the potential administration of hemopexin in hemolytic disorders.
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Affiliation(s)
- Milena Sophie Detzel
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
| | - Benjamin Franz Schmalohr
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
| | - Francèl Steinbock
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
| | - Marie-Thérèse Hopp
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
| | - Anuradha Ramoji
- Center for Sepsis Control and Care (CSCC), Jena University Hospital, D-07747Jena, Germany.,Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, D-07745Jena, Germany
| | - Ajay Abisheck Paul George
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
| | - Ute Neugebauer
- Center for Sepsis Control and Care (CSCC), Jena University Hospital, D-07747Jena, Germany.,Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, D-07745Jena, Germany
| | - Diana Imhof
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121Bonn, Germany
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