Mycobacterium tuberculosis PanD structure-function analysis and identification of a potent pyrazinoic acid-derived enzyme inhibitor

Abstract

A common strategy employed in antibacterial drug discovery is targeting of biosynthetic processes which are essential and specific for the pathogen. Specificity in particular avoids undesirable interactions with potential enzymatic counterparts in the human host, and ensures on-target toxicity. Synthesis of pantothenate (Vitamine B5), a precursor of the acyl carrier coenzyme A, is an example of such a pathway. In Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), pantothenate is formed by pantothenate synthase, utilizing D-pantoate and βAla as substrates. β-Ala is mainly formed by the decarboxylation of L-aspartate, generated by the decarboxylase PanD, a homo-oliogomer in solution. Pyrazinoic acid (POA), the bioactive form of the TB prodrug pyrazinamide, binds and inhibits PanD activity weakly. Here, we generated a library of recombinant Mtb PanD mutants based on structural information and PZA/POA resistance mutants. Alterations in oligomer formation, enzyme activity and/or POA binding were observed in respective mutants, providing insights into essential amino acids for Mtb PanD’s proper structural assembly, decarboxylation activity and drug interaction. This information provided the platform for the design of novel POA analogs with modifications at position 3 of the pyrazine ring. Analog 2, incorporating a bulky naphthamido group at this position, displayed a 1,000-fold increase in enzyme inhibition compared to POA, along with moderately improved antimycobacterial activity. The data demonstrate that an improved understanding of mechanistic and enzymatic features of key metabolic enzymes can stimulate design of more potent PanD inhibitors.