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07:51
Pull-down of Calmodulin-binding Proteins
Published on: January 23, 2012
The second Ca(2+)-binding domain of NCX1 binds Mg2+ with high affinity
Vincent Breukels1, Albert Konijnenberg, Sanne M Nabuurs
1Protein Biophysics, Institute for Molecules and Materials, Radboud University Nijmegen, 6525 GA Nijmegen, The Netherlands.
Biochemistry
|September 21, 2011
Summary
Magnesium ions (Mg2+) bind to the sodium-calcium exchanger's second calcium-binding domain (CBD2), preferentially at site II. This Mg2+ binding stabilizes CBD2 and alters its calcium (Ca2+) affinity, impacting ion exchange.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- The sodium-calcium exchanger regulates intracellular calcium levels.
- Its second calcium-binding domain (CBD2) is crucial for function and binds calcium ions (Ca2+).
- The role of magnesium ions (Mg2+) in CBD2 function is not well understood.
Purpose of the Study:
- To investigate the effects of Mg2+ binding on CBD2 structure and function.
- To determine the binding sites and affinities of Mg2+ in CBD2.
- To elucidate how Mg2+ binding influences Ca2+ binding and CBD2 stability.
Main Methods:
- Nuclear magnetic resonance (NMR) spectroscopy
- Circular dichroism (CD) spectroscopy
- Isothermal titration calorimetry (ITC)
- Site-directed mutagenesis
Main Results:
- CBD2 binds Mg2+ at both Ca2+-binding sites I and II, with different affinities.
- Ca2+ can displace Mg2+ from site I but not site II.
- Mg2+ binding stabilizes CBD2, as shown by thermal unfolding CD.
- NMR data indicate Mg2+-bound CBD2 adopts an intermediate conformation.
- Mg2+ preferentially binds to site II at physiological concentrations.
Conclusions:
- Mg2+ binding to CBD2 stabilizes the domain and alters its Ca2+ affinity.
- Preferential Mg2+ binding at site II influences the exchanger's ion-binding properties.
- These findings provide new insights into the regulation of sodium-calcium exchange by divalent cations.
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