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NMR characterization of structure, backbone dynamics, and glutathione binding of the human macrophage migration
P Mühlhahn1, J Bernhagen, M Czisch
1Max Planck Institute for Biochemistry, Martinsried, Germany.
Abstract:
Human macrophage migration inhibitory factor is a 114 amino acid protein that belongs to the family of immunologic cytokines. Assignments of 1H, 15N, and 13C resonances have enabled the determination of the secondary structure of the protein, which consists of two alpha-helices (residues 18-31 and 89-72) and a central four-stranded beta-sheet. In the beta-sheet, two parallel beta-sheets are connected in an antiparallel sense. From the total of three cysteines present in the primary structure of MIF, none was found to form disulfide bridges. 1H-15N heteronuclear T1, T2, and steady-state NOE measurements indicate that the backbone of MIF exists in a rigid structure of limited conformational flexibility (on the nanosecond to picosecond time scale). Several residues located in the loop regions and at the N termini of two helices exhibit internal motions on the 1-3 ns time scale. The capacity to bind glutathione was investigated by titration of a uniform 15N-labeled sample and led us to conclude that MIF has, at best, very low affinity for glutathione.
Insights
Human macrophage migration inhibitory factor (MIF) is an immunologic cytokine with a rigid backbone structure. Studies reveal limited conformational flexibility and low affinity for glutathione binding.
Area of Science:
- Biochemistry
- Structural Biology
- Immunology
Background:
- Human macrophage migration inhibitory factor (MIF) is a key immunologic cytokine.
- Understanding MIF's structure and dynamics is crucial for its biological function.
Purpose of the Study:
- To determine the secondary and tertiary structure of human MIF.
- To investigate the conformational flexibility and dynamics of MIF.
- To assess the binding affinity of MIF to glutathione.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 15N, 13C) for resonance assignments and structure determination.
- Heteronuclear NMR relaxation measurements (T1, T2, NOE) to probe backbone dynamics.
- Glutathione titration experiments to evaluate binding affinity.
Main Results:
- The secondary structure of MIF comprises two alpha-helices and a central four-stranded antiparallel beta-sheet.
- No disulfide bridges were detected among the three cysteine residues.
- NMR data indicate a rigid MIF backbone with limited flexibility on the nanosecond to picosecond timescale.
- Specific loop regions and N-termini of helices show internal motions on the 1-3 ns timescale.
- MIF exhibits very low affinity for glutathione binding.
Conclusions:
- Human MIF possesses a well-defined, rigid structure with localized internal motions.
- The lack of disulfide bridges and low glutathione affinity suggest these are not primary functional mechanisms for MIF.