Structure and function of non-native metal clusters in human arginase I
Edward L D'Antonio1, Yang Hai, David W Christianson
1Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Biochemistry
|October 16, 2012
Summary
Manganese (Mn2+) is essential for optimal human arginase I activity. Substituting metal ions like nickel (Ni2+) or zinc (Zn2+) alters enzyme structure and function, with Zn2+ inhibiting catalysis by binding to key residues.
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Human arginase I is a binuclear manganese-dependent enzyme crucial for urea cycle function.
- Understanding the role of metal ions in arginase catalysis is vital for enzyme engineering and therapeutic development.
Purpose of the Study:
- To investigate the structural and functional impact of substituting the native manganese (Mn2+) cluster in human arginase I with other metal ions.
- To elucidate the mechanism of zinc (Zn2+) inhibition in human arginase I.
Main Methods:
- Reconstitution of crystalline human arginase I with various metal ions (Ni2+, Zn2+, Co2+) after apoenzyme formation.
- X-ray crystallography to determine the structures of metal ion variants.
- Enzyme kinetics assays to measure catalytic activity (kcat, kcat/KM) and substrate analogue binding.
Main Results:
- Structural and activity analyses revealed distinct differences upon metal ion substitution.
- Zinc (Zn2+) was found to inhibit catalysis by forming a specific triad with histidine (H141) and glutamate (E277).
- The substrate analogue 2(S)-amino-6-boronohexanoic acid (ABH) binds to various metal clusters, indicating potential for catalysis with different ions.
- Catalytic efficiency followed the trend: Mn2+ > Ni2+ ≈ Co2+ ≫ Zn2+.
Conclusions:
- Manganese (Mn2+) is indispensable for optimal human arginase I catalytic activity.
- Zinc (Zn2+) acts as an inhibitor through specific structural interactions, offering insights into enzyme regulation.
- The study provides a structural basis for understanding metal ion-dependent catalysis and inhibition in arginase I.
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