Structure of cytochrome in complex with Q203 and TB47, two anti-TB drug candidates.

Pathogenic mycobacteria pose a sustained threat to global human health. Recently, cytochrome complexes have gained interest as targets for antibiotic drug development. However, there is currently no structural information for the cytochrome complex from these pathogenic mycobacteria. Here, we report the structures of cytochrome alone (2.68 Å resolution) and in complex with clinical drug candidates Q203 (2.67 Å resolution) and TB47 (2.93 Å resolution) determined by single-particle cryo-electron microscopy. cytochrome forms a dimeric assembly with endogenous menaquinone/menaquinol bound at the quinone/quinol-binding pockets. We observe Q203 and TB47 bound at the quinol-binding site and stabilized by hydrogen bonds with the side chains of Thr and Glu, residues that are conserved across pathogenic mycobacteria. These high-resolution images provide a basis for the design of new mycobacterial cytochrome inhibitors that could be developed into broad-spectrum drugs to treat mycobacterial infections.