Many targets: how a TB drug hits Mycobacterium tuberculosis multiple ways

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains difficult to treat because standard therapy requires at least six months of multiple antibiotics. There is growing interest in using β-lactam antibiotics to help improve treatment outcomes for people with TB, but it has not been clear which Mtb enzymes those drugs actually hit inside the bacterium. In a study led by Kimberly E. Beatty, researchers set out to build a comprehensive picture of the enzymes in Mtb that are vulnerable to β-lactam antibiotics. To make their findings relevant to disease, they examined bacterial proteins under physiological conditions meant to represent both acute and chronic TB. Rather than inferring targets from genetic data or isolated enzymes alone, the team used chemical probes that act like the drugs themselves. Those probes directly tag the active sites of enzymes that recognize and react with β-lactams, allowing the scientists to detect which proteins are engaged by these antibiotics in realistic settings. This approach was designed to give a clearer map of how β-lactam drugs interact with Mtb at the biochemical level.

The central tool in the study was a set of new activity-based probes based on the β-lactam antibiotic meropenem, chosen in part because meropenem has been approved by the World Health Organization for TB treatment. Activity-based probes label enzymes according to both substrate specificity and catalytic mechanism, so they can reveal which proteins a drug actually targets. Using these meropenem-based probes, the team identified previously undiscovered targets in addition to the expected cell wall biosynthetic enzymes. They validated β-lactam binding and hydrolysis for six newly identified targets, naming them exactly as Rv1723, Rv2257c, Rv0309, DapE (Rv1202), MurI (Rv1338), and LipD (Rv1923). Beyond these six, the results indicate that there are at least 30 enzymes in Mtb vulnerable to inhibition by meropenem. That number is many more β-lactam targets than had been historically described, highlighting a breadth of interaction between meropenem and Mtb proteins.

These findings point to a different way of thinking about how β-lactam antibiotics work against Mtb: rather than acting on a single essential enzyme, efficacy may come from polypharmacology, where one drug inhibits many targets at once. Demonstrating that meropenem can engage at least 30 different Mtb enzymes expands the biochemical map researchers can use to predict drug activity, potential synergies with other antibiotics, and likely mechanisms of action. The identified proteins, including Rv1723, Rv2257c, Rv0309, DapE (Rv1202), MurI (Rv1338), and LipD (Rv1923), provide specific entry points for further study of how β-lactams affect cell wall biosynthesis and other pathways in both acute and chronic disease states. By using activity-based probes under physiologically relevant conditions, the study gives a concrete inventory of vulnerable enzymes that can guide future laboratory work, drug combinations, and the design of next-generation inhibitors that exploit the same multi-target behavior.