Cryo-EM structure of the transcription termination factor Rho from Mycobacterium tuberculosis reveals mechanism of resistance to bicyclomycin
The bacterial Rho factor is a ring-shaped motor triggering genome-wide transcription termination and R-loop dissociation. Rho is essential in many species, including in Mycobacterium tuberculosis where rho gene inactivation leads to rapid death. Yet, the M. tuberculosis Rho [MtbRho] factor displays poor NTPase and helicase activities, and resistance to the natural Rho inhibitor bicyclomycin [BCM] that remain unexplained. Here, we address these unusual features by solving the cryo-EM structure of MtbRho at 3.3 [A] resolution, providing a new framework for future antibiotic development. The MtbRho hexamer is poised into a pre-catalytic, open-ringed state wherein specific contacts stabilize ATP in intersubunit ATPase pockets, thereby explaining the cofactor preference of MtbRho. We reveal a leucine-to-methionine substitution that creates a steric bulk in BCM binding cavities near the positions of ATP {gamma}-phosphates, and confers resistance to BCM at the expense of motor efficiency.