Abstract
The imidazopyridine telacebec, also known as Q203, is one of only a few new classes of compounds in more than 50 years with demonstrated antituberculosis activity in humans. Telacebec inhibits the mycobacterial respiratory supercomplex composed of complexes III and IV (CIII2CIV2). In mycobacterial electron transport chains, CIII2CIV2 replaces canonical CIII and CIV, transferring electrons from the intermediate carrier menaquinol to the final acceptor, molecular oxygen, while simultaneously transferring protons across the inner membrane to power ATP synthesis. We show that telacebec inhibits the menaquinol:oxygen oxidoreductase activity of purified Mycobacterium smegmatis CIII2CIV2 at concentrations similar to those needed to inhibit electron transfer in mycobacterial membranes and Mycobacterium tuberculosis growth in culture. We then used electron cryomicroscopy (cryoEM) to determine structures of CIII2CIV2 both in the presence and absence of telacebec. The structures suggest that telacebec prevents menaquinol oxidation by blocking two different menaquinol binding modes to prevent CIII2CIV2 activity.
Highlights
Numerous bacteria from the strictly aerobic genus Mycobacterium are human pathogens
In order facilitate isolation of CIII2CIV2, we used the oligonucleotide-mediated recombineering followed by Bxb integrase targeting (ORBIT) strategy (Murphy et al, 2018) to introduce sequence for a 3 FLAG affinity tag into the chromosomal DNA of M. smegmatis immediately 3
While M. smegmatis is typically grown in 7H9 medium supplemented with albumin, dextrose, and sodium chloride (ADS), we found that supplementing instead with tryptone, dextrose, and sodium chloride (TDS), which is more economical for large scale culture, gave equivalent or superior growth
Summary
Numerous bacteria from the strictly aerobic genus Mycobacterium are human pathogens. Infection by Mycobacterium tuberculosis and closely related species result in the disease tuberculosis (TB). In most years TB is the leading cause of death by infectious disease internationally, with an increasing incidence of drug-resistant infections Nontuberculosis mycobacterial pathogens include M. leprae, which causes leprosy, M. ulcerans, which causes Buruli ulcer, and M. avium and M. abscessus, which infect immunocompromised and cystic fibrosis patients, respectively. The discovery of bedaquiline from a phenotypic screen with non-pathogenic M. smegmatis, and its subsequent development into an effective therapeutic, has revolutionized the treatment of multidrug-resistant and extensively drug-resistant TB (Global Tuberculosis Report, 2020; World Health Organization, 2019). Bedaquiline binds the membrane region of mycobacterial ATP synthase (Andries et al., 2005; Guo et al, 2021; Preiss et al, 2015), blocking proton translocation and ATP synthesis
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