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Updated: May 13, 2025
Paramagnetic Relaxation Enhancement for Detecting and Characterizing Self-Associations of Intrinsically Disordered Proteins
Published on: September 23, 2021
Excellent Fe(II) Binding Tag in Protein Paramagnetic NMR Spectroscopy
Mo-Han Li1, Xing Zhang1, Bin-Bin Pan1
1State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
A novel iron-binding ligand, [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylic acid (TDA), enables precise measurement of iron(II) magnetic anisotropy in proteins using pseudocontact shifts (PCSs). This stable complex functions effectively even in complex biological environments.
Area of Science:
- Biophysical Chemistry
- Structural Biology
- Bioinorganic Chemistry
Background:
- Transition metal ions exhibit diverse paramagnetic properties due to unpaired electrons.
- Magnetic anisotropy of metal ions like Co(II) and Ln(III) is well-studied in proteins via NMR.
- Few studies have analyzed Fe(II) magnetic anisotropy in proteins outside heme or iron-sulfur clusters.
Purpose of the Study:
- To introduce [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylic acid (TDA) as a novel iron-binding ligand for protein studies.
- To investigate the iron-binding properties and complex stability of TDA with Fe(II) and Fe(III).
- To assess the utility of TDA-metal complexes for measuring magnetic anisotropy in proteins using NMR.
Main Methods:
- Synthesis and characterization of the TDA ligand.
- Formation and stability assessment of TDA complexes with Fe(II) and Fe(III) in aqueous solution.
- Site-specific attachment of TDA to proteins.
- Measurement of pseudocontact shifts (PCSs) and paramagnetic relaxation enhancement (PRE) using NMR spectroscopy.
Main Results:
- TDA forms a stable 1:1 complex with both Fe(II) and Fe(III).
- Fe(II)-TDA complex exhibits a high-spin state, generating significant PCSs in protein conjugates, exceeding those of common tags.
- Fe(III)-TDA complex shows a low-spin state with negligible PRE effects.
- The protein-TDA-Fe(II) complex is stable in cell lysate, allowing accurate PCS measurements.
Conclusions:
- TDA is an excellent ligand for studying Fe(II) magnetic anisotropy in proteins via PCS.
- The TDA-Fe(II) system offers a robust tool for structural biology, even in complex biological samples.
- TDA provides a valuable alternative to existing metal-binding tags for NMR-based structural studies.
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