Investigations of the Pup-Proteasome System in Mycobacterium tuberculosis

Abstract

Protein degradation via the proteasome is essential for full virulence of the pathogen Mycobacterium tuberculosis. The enzyme PafA regulates degradation by the conjugation of prokaryotic ubiquitin-like protein (Pup) to protein substrates. A rational, structure-based approach was used to design a peptidic inhibitor to target the PafA-Pup interface. Robust inhibition of pupylation was observed both in vitro and in cellular lysate, which in conjunction with the proven site-specificity of this interaction, has validated PafA as a druggable target in M. tuberculosis. In addition, a proteasome-independent role for pupylation was investigated through 1H NMR spectroscopy studies measuring the rate of the PanB-catalyzed formation of ketopantoate. Pupylation was found to enhance PanB activity suggesting that an increase in the population of Pup-PanB under conditions of stress may also enhance downstream processes responsible for the formation of the waxy cell wall protecting M. tuberculosis against the host immune response.