Discovery and Mechanistic Study of Mycobacterium tuberculosis PafA Inhibitors

Tuberculosis is caused by the bacterium Mycobacterium
tuberculosis (Mtb) and is ranked
as the second killer infectious disease after COVID-19. Proteasome
accessory factor A (PafA) is considered an attractive target because
of its low sequence conservation in humans and its role in virulence.
In this study, we designed a mutant of Mtb PafA that
enabled large-scale purification of active PafA. Using a devised high-throughput
screening assay, two PafA inhibitors were discovered. ST1926 inhibited Mtb PafA by binding in the Pup binding groove, but it was
less active against Corynebacterium glutamicum PafA because the ST1926-binding residues are not conserved. Bithionol
bound to the conserved ATP-binding pocket, thereby, inhibits PafA
in an ATP-competitive manner. Both ST1926 and bithionol inhibited
the growth of an attenuated Mtb strain (H37Ra) at
micromolar concentrations. Our work thus provides new tools for tuberculosis
research and a foundation for future PafA-targeted drug development
for treating tuberculosis.