The anti-tubercular callyaerins target the Mycobacterium tuberculosis-specific non-essential membrane protein Rv2113

Spread of antimicrobial resistances in the pathogen Mycobacterium tuberculosis remains a public health challenge. Thus, there is a continuous need for new therapeutic options with modes-of-action differing from current antibiotics. Previously, bioactivity-guided isolation identified the callyaerins, a class of hydrophobic cyclopeptides with an unusual (Z)-2,3-di-aminoacrylamide unit, as promising antitubercular agents. In this study, we investigated the molecular mechanisms underlying their antimycobacterial properties. Structure-activity relationship studies enabled the identification of the structural determinants relevant for their antibacterial activity. The antitubercular callyaerins are bacteriostatics selectively active against M. tuberculosis, including extensively drug-resistant (XDR) strains, with minimal cytotoxicity against human cells and a promising intracellular activity in a macrophage infection model. Via spontaneous resistance mutant screens and various chemical proteomics approaches, we showed that they act by direct targeting of the non-essential, M. tuberculosis-specific putative membrane protein Rv2113, thereby triggering a complex stress response in M. tuberculosis characterized by global downregulation of lipid biosynthesis, cell division, DNA repair and replication. Our study thus not only identifies Rv2113 as a new M. tuberculosis-specific target for antitubercular drugs, which should result in less harm of the microbiome and weaker resistance development in off-target pathogens. It furthermore demonstrates that also non-essential proteins may represent efficacious targets for antimycobacterial drugs.