A Ketol-Acid Reductoisomerase Inhibitor That Has Antituberculosis and Herbicidal Activity

Area of Science:

• Biochemistry
• Microbiology
• Drug Discovery

Background:

• Ketol-acid reductoisomerase (KARI) is essential for branched-chain amino acid biosynthesis in microbes and plants, making it a target for biocidal agents.
• Previous KARI inhibitors faced limitations due to substrate competition and slow binding kinetics, reducing efficacy when substrate (2-acetolactate) accumulates.

Purpose of the Study:

• To identify and characterize novel KARI inhibitors with improved biocidal potential.
• To investigate the inhibition mechanism of a pyrimidinedione compound (1f) against KARI from different species.

Main Methods:

• Enzyme inhibition assays were performed for Mycobacterium tuberculosis KARI (MtKARI) and Oryza sativa KARI (OsKARI).
• Time-dependent inhibition kinetics were assessed for compound 1f.
• Crystal structure analysis of compound 1f bound to Staphylococcus aureus KARI (SaKARI) was conducted.
• Minimum Inhibitory Concentration (MIC) was determined for MtH37Rv, and plant growth inhibition was tested for Brassica campestris.

Main Results:

• Compound 1f acts as a competitive and time-dependent inhibitor of MtKARI for both 2-acetolactate (AL) and NADPH (Ki = 23.3 nM).
• Crystal structure revealed dual competition for MtKARI.
• 1f inhibited OsKARI competitively for AL and uncompetitively for NADPH, without time-dependent inhibition.
• 1f demonstrated antimicrobial activity with an MIC of 12.7 µM against MtH37Rv and inhibited plant growth.

Conclusions:

• KARI inhibitors that are competitive for NADPH and lack time-dependent inhibition show significant potential as biocides.
• Compound 1f serves as a lead for developing novel biocidal agents targeting KARI in pathogens and weeds.