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Related Experiment Videos

Specific potassium binding stabilizes pI258 arsenate reductase from Staphylococcus aureus.

Nina Lah1, Jurij Lah, Ingrid Zegers

  • 1Department Ultrastructure, Vlaams interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel, Pleinlaan 2, Belgium. nina.lah@uni-lj.si

The Journal of Biological Chemistry
|April 19, 2003
PubMed
Summary

Potassium ions stabilize Staphylococcus aureus arsenate reductase (ArsC), enhancing its thermal stability and increasing its activity. This binding is an enthalpic process involving specific amino acid residues.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Arsenate reductase (ArsC) from Staphylococcus aureus facilitates bacterial heavy metal resistance by reducing arsenate to arsenite.
  • The enzyme's structure reveals a potassium (K+) binding site adjacent to its catalytic P-loop.
  • Understanding cation interactions is crucial for elucidating enzyme function and stability.

Purpose of the Study:

  • To investigate the binding characteristics of monovalent cations with ArsC.
  • To determine the influence of these cations on the enzyme's thermal stability.
  • To identify key residues involved in cation binding and their impact on enzyme activity and stability.

Main Methods:

  • Isothermal titration calorimetry (ITC) for thermodynamic binding studies.

Related Experiment Videos

  • Circular dichroism (CD) spectroscopy and differential scanning calorimetry (DSC) for thermal stability analysis.
  • Site-directed mutagenesis to probe the roles of specific amino acid residues.

    • Main Results:

    • Potassium (K+) exhibits the highest binding affinity (Ka = 3.8 x 10^3 M^-1) among tested monovalent cations.
    • Cation stabilization effectiveness follows the order: K+ > Rb+ > Cs+ > Na+ > Li+.
    • Mutagenesis revealed Asn-13, Asp-65, and particularly Ser-36 as critical for K+ binding and stability; E21A mutation highlighted the role of a water molecule in K+ interaction.
    • K+ binding, while not essential for catalysis, increases ArsC's catalytic efficiency (kcat/KM) by fivefold.

    Conclusions:

    • The interaction between K+ and ArsC is an enthalpy-driven process.
    • K+ binding significantly enhances ArsC's thermal stability and specific activity.
    • Specific residues, including Ser-36 and a Glu-21-coordinated water molecule, are vital for K+ interaction and enzyme stabilization.