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Nitrite Reductase Activity in Engineered Azurin Variants.

Steven M Berry1, Jacob N Strange1, Erika L Bladholm1

  • 1Department of Chemistry and Biochemistry, University of Minnesota Duluth , 1039 University Drive, Duluth, Minnesota 55812, United States.

Inorganic Chemistry
|April 8, 2016
PubMed
Summary
This summary is machine-generated.

Researchers engineered azurin variants with new copper sites to study nitrite reductase activity. These modified proteins showed catalytic function, demonstrating electron transfer from both copper centers, with the T2 site being crucial for steady-state catalysis.

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Area of Science:

  • Biochemistry
  • Bioinorganic Chemistry
  • Enzyme Engineering

Background:

  • Nitrite reductase (NiR) is a crucial enzyme in the nitrogen cycle, catalyzing the reduction of nitrite to nitric oxide.
  • Understanding the mechanisms of dinuclear copper enzymes like NiR is vital for developing biomimetic catalysts.
  • Azurin, a small blue copper protein, serves as a versatile scaffold for engineering novel metalloenzymes.

Purpose of the Study:

  • To engineer P.a. azurin variants with a second, surface-bound copper site mimicking NiR's catalytic center.
  • To investigate the nitrite reductase activity and catalytic mechanism of these novel dicopper azurin variants.
  • To explore the role of individual copper centers in the electron transfer and catalytic process.

Main Methods:

  • Site-directed mutagenesis was employed to introduce copper-binding motifs into the azurin scaffold.
  • Spectroscopic techniques (UV-visible absorption, EPR) and electrochemistry were used to characterize the engineered copper sites.
  • Enzyme kinetics, including Michaelis-Menten parameters, were determined for nitrite reduction activity.

Main Results:

  • Four azurin variants (Az-NiR, Az-NiR3His, Az-PHM, Az-PHM3His) with functional second copper sites were successfully synthesized.
  • The variants exhibited nitrite reductase activity, albeit slower than native NiRs, comparable to other model systems.
  • Catalysis was reversible (NO to nitrite), and electron transfer involved both copper centers, with the T2 site essential for steady-state catalysis.

Conclusions:

  • Engineered azurin variants can successfully incorporate functional copper sites for nitrite reduction.
  • The study provides insights into the mechanism of dinuclear copper enzymes and the role of different copper centers.
  • These findings contribute to the development of biomimetic catalysts for nitrogen cycle-related reactions.