A trans-translation inhibitor that targets ribosomal protein bL12 kills Mycobacterium tuberculosis

New antibiotics with novel mechanisms of action are needed to treat infections by multidrug-resistant strains of Mycobacterium tuberculosis. Here, we show that KKL-1005, an anti-tubercular triazole-based molecule, binds to ribosomal protein bL12 and specifically inhibits the trans-translation ribosome rescue pathway, a process essential for the survival of M. tuberculosis. Our data demonstrate that KKL-1005 binds to the N-terminal domain of bL12, both in vitro and in bacterial cells, and specifically inhibits trans-translation and not normal translation. These results suggest that tmRNA-SmpB interacts with bL12 differently from tRNA and raise the possibility of developing antibiotics targeting bL12.IMPORTANCETuberculosis continues to be a leading cause of death worldwide, and antibiotics that target new pathways are urgently needed. trans-Translation is a ribosome rescue pathway required for the survival of Mycobacterium tuberculosis. We identified a small molecule, KKL-1005, that specifically inhibits trans-translation without affecting translation from a library of compounds that prevent the growth of M. tuberculosis. KKL-1005 targets bacterial ribosomal protein bL12, which is essential for the recruitment and activation of GTPase translation factors. The specificity of KKL-1005 for trans-translation indicates that bL12 interacts differently with the translation machinery during trans-translation than during canonical translation. KKL-1005 is bactericidal against M. tuberculosis, suggesting that inhibiting trans-translation by targeting bL12 is a new strategy for developing antibiotics against drug-resistant infections.