E. coli Ribonucleotide Reductase β2 Subunit Inactivation by Triapine Occurs through Binding of a Triapine-Fe(II)...

Area of Science:

• Biochemistry
• Molecular Biology
• Medicinal Chemistry

Background:

• Ribonucleotide reductase (RNR) is crucial for DNA synthesis and repair, making it a significant therapeutic target in various diseases.
• Triapine (3AP) is a small molecule inhibitor of RNR, specifically targeting the tyrosyl radical in the RNR β2 subunit.

Purpose of the Study:

• To mechanistically investigate the inhibition of the RNR β2 subunit by the triapine-iron(II) adduct.
• To elucidate the role of proton transfer in the inhibition process and compare it with other RNR inhibitors like hydroxyurea.

Main Methods:

• Utilized solvent kinetic isotope effects to assess the rate-limiting steps in the inhibition.
• Employed vibrational spectroscopy to investigate the involvement of proton transfer pathways.
• Performed binding measurements to determine the affinity of the triapine-iron(II) adduct for the RNR β2 subunit.

Main Results:

• Proton transfer is not the rate-limiting step for the inhibition of the Y122· radical in E. coli RNR β2 by the 3AP-Fe(II) adduct.
• Unlike hydroxyurea, the inhibition mechanism by triapine does not involve a carboxylate-containing proton wire.
• The 3AP-Fe(II) adduct exhibits a high binding affinity (Kd ≈ 6 nM) for the RNR β2 subunit.

Conclusions:

• The findings provide a detailed mechanistic understanding of triapine's inhibition of RNR.
• The triapine scaffold shows promise for developing novel RNR inactivators for therapeutic applications.
• Further development of triapine-based RNR inhibitors is warranted for treating diseases associated with RNR dysregulation.