title: The Mycobacterium tuberculosis outer membrane channel protein CpnT confers susceptibility to toxic molecules.
abstract: Mycobacterium tuberculosis, the causative agent of tuberculosis, is protected from toxic solutes by an effective outer membrane permeability barrier. Recently, we showed that the outer membrane channel protein CpnT is required for efficient nutrient uptake by M. tuberculosis and Mycobacterium bovis BCG. In this study, we found that the cpnT mutant of M. bovis BCG is more resistant than the wild type to a large number of drugs and antibiotics, including rifampin, ethambutol, clarithromycin, tetracycline, and ampicillin, by 8- to 32-fold. Furthermore, the cpnT mutant of M. bovis BCG was 100-fold more resistant to nitric oxide, a major bactericidal agent required to control M. tuberculosis infections in mice. Thus, CpnT constitutes the first outer membrane susceptibility factor in slow-growing mycobacteria. The dual functions of CpnT in uptake of nutrients and mediating susceptibility to toxic molecules are reflected in macrophage infection experiments: while loss of CpnT was detrimental for M. bovis BCG in macrophages that enable bacterial replication, presumably due to inadequate nutrient uptake, it conferred a survival advantage in macrophages that mount a strong bactericidal response. Importantly, the cpnT gene showed a significantly higher density of nonsynonymous mutations in drug-resistant clinical M. tuberculosis strains, indicating that CpnT is under selective pressure in human tuberculosis and/or during chemotherapy. Our results indicate that the CpnT channel constitutes an outer membrane gateway controlling the influx of nutrients and toxic molecules into slow-growing mycobacteria. This study revealed that reducing protein-mediated outer membrane permeability might constitute a new drug resistance mechanism in slow-growing mycobacteria.
authors: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors: Olga
authors: O
authors: Danilchanka
authors: Centro de Patogénese Molecular-URIA/Instituto de Medicina Molecular, Instituto de Investigação do Medicamento, iMed-ULisboa, Faculdade de Farmácia da Universidade de Lisboa, Lisbon, Portugal.
authors: David
authors: D
authors: Pires
authors: Centro de Patogénese Molecular-URIA/Instituto de Medicina Molecular, Instituto de Investigação do Medicamento, iMed-ULisboa, Faculdade de Farmácia da Universidade de Lisboa, Lisbon, Portugal eanes@ff.ul.pt mnieder@uab.edu.
authors: Elsa
authors: E
authors: Anes
authors: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, USA eanes@ff.ul.pt mnieder@uab.edu.
authors: Michael
authors: M
authors: Niederweis
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects* / Q000235:genetics*; D001427:Bacterial Toxins; D002460:Cell Line; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006801:Humans; D053583:Interleukin-1beta / Q000096:biosynthesis; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D009569:Nitric Oxide / Q000494:pharmacology; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001427:Bacterial Toxins; D053583:Interleukin-1beta; C000589201:Rv3903 protein, Mycobacterium tuberculosis; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II
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