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Site-specific labelling with a metal chelator for protein-structure refinement.
Guido Pintacuda1, Ahmad Moshref, Ainars Leonchiks
1Department of Medical Biochemistry and Biophysics, Karolinska Institute, S-171 77 Stockholm, Sweden.
Journal of Biomolecular NMR
|June 24, 2004
Summary
This study introduces a method to attach paramagnetic metal ions to proteins for structural analysis. This technique provides long-range distance restraints crucial for studying protein structures, especially solvent-exposed loops.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Site-specific modification of proteins is essential for structural studies.
- Paramagnetic metal ions can provide long-range structural information.
- Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for protein structure determination.
Purpose of the Study:
- To develop a method for site-specific attachment of paramagnetic metal ions to proteins.
- To utilize paramagnetic effects for determining long-range distance restraints in proteins.
- To refine protein structures using paramagnetic restraints in regions inaccessible to traditional methods like Nuclear Overhauser Effect (NOE).
Main Methods:
- Covalent derivatization of a free cysteine (Cys) in the E. coli arginine repressor with S-cysteaminyl-EDTA.
- Site-specific attachment of paramagnetic metal ions (Co(2+), Cu(2+), Mn(2+)) to the EDTA moiety.
- Monitoring effects of metal ion complexation using (15)N-HSQC NMR spectra.
- Analysis of pseudocontact shifts and paramagnetic relaxation enhancements (T(1) and T(2)) of amide protons.
- Determination of electronic correlation times for Cu(2+) and Mn(2+).
Main Results:
- Complexation with Co(2+) induced pseudocontact shifts and peak doubling, suggesting stereoisomer formation.
- Complexation with Cu(2+) or Mn(2+) yielded paramagnetic relaxation enhancements without significant chemical shift changes.
- Combined T(1) relaxation enhancements with Cu(2+) and T(2) relaxation enhancements with Mn(2+) provided accurate distance restraints from 9 to 25 Å.
- The structure of a solvent-exposed loop in the E. coli arginine repressor was refined using these paramagnetic restraints.
Conclusions:
- Paramagnetic relaxation enhancements from Cu(2+) and Mn(2+) offer valuable long-range distance restraints for protein structural studies.
- This method extends structural analysis to regions not amenable to NOE-based approaches.
- The technique is effective for refining structures of solvent-exposed loops and potentially other protein domains.