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On the competition for available zinc.
Uwe Heinz1, Martin Kiefer, Andreas Tholey
1Department of Natural Sciences, The Royal Veterinary and Agricultural University, DK-1871 Frederiksberg C, Denmark.
The Journal of Biological Chemistry
|November 13, 2004
Summary
This study reveals rapid zinc ion transfer between peptides and EDTA, driven by ligand exchange, not simple dissociation. Zinc-bridged complexes form when peptides exceed available zinc, impacting protein structural zinc sites.
Area of Science:
- Biochemistry
- Biophysical Chemistry
- Spectroscopy
Background:
- Proteins utilize structural zinc sites for stability and function.
- Zinc finger (C2H2) and tetrathiolate (C4) peptides mimic these protein zinc-binding sites.
- These peptides exhibit rapid zinc ion binding with high affinity.
Purpose of the Study:
- To investigate zinc binding mechanisms to C2H2 and C4 peptides.
- To elucidate the kinetics and thermodynamics of zinc ion transfer.
- To characterize the structural aspects of zinc-peptide complexes.
Main Methods:
- Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy.
- Thermodynamic and kinetic analyses.
- Competition assays with EDTA.
Main Results:
- Zinc transfer to EDTA is 6 orders of magnitude faster than predicted by dissociation-association.
- EXAFS confirmed Cys2His2 geometry for C2H2 and revealed zinc-bridged complexes with sulfur coordination in excess peptide.
- Kinetic analysis suggested complex mechanisms for C4 involving bridged and partially coordinated species.
Conclusions:
- Ligand exchange mechanisms, not dissociation-association, dominate rapid zinc transfer.
- Zinc-bridged complexes form under conditions of peptide excess.
- Kinetic instability of zinc-peptide complexes facilitates rapid zinc ion exchange.