Novel inhibitors of cholesterol degradation in mycobacterium tuberculosis reveal how the bacterium’s metabolism is constrained by the intracellular environment


Mycobacterium tuberculosis (Mtb) relies on a specialized set of metabolic pathways to support growth in macrophages. By conducting an extensive, unbiased chem. screen to identify small mols. that inhibit Mtb metab. within macrophages, we identified a significant no. of novel compds. that limit Mtb growth in macrophages and in medium contg. cholesterol as the principle carbon source. Based on this observation, we developed a chem.-rescue strategy to identify compds. that target metabolic enzymes involved in cholesterol metab. This approach identified two compds. that inhibit the HsaAB enzyme complex, which is required for complete degrdn. of the cholesterol A/B rings. The strategy also identified an inhibitor of PrpC, the 2-methylcitrate synthase, which is required for assimilation of cholesterol-derived propionyl-CoA into the TCA cycle. These chem. probes represent new classes of inhibitors with novel modes of action, and target metabolic pathways required to support growth of Mtb in its host cell. The screen also revealed a structurally-diverse set of compds. that target addnl. stage(s) of cholesterol utilization. Mutants resistant to this class of compds. are defective in the bacterial adenylate cyclase Rv1625/Cya. These data implicate cyclic-AMP (cAMP) in regulating cholesterol utilization in Mtb, and are consistent with published reports indicating that propionate metab. is regulated by cAMP levels. Intriguingly, reversal of the cholesterol-dependent growth inhibition caused by this subset of compds. could be achieved by supplementing the media with acetate, but not with glucose, indicating that Mtb is subject to a unique form of metabolic constraint induced by the presence of cholesterol. [on SciFinder(R)]

PLoS Pathog