A Mycobacterium tuberculosis Effector Targets Mitochondrion, Controls Energy Metabolism, and Limits Cytochrome c Exit.

Host metabolism reprogramming is a key feature of Mycobacterium tuberculosis (Mtb) infection that enables the survival of this pathogen within phagocytic cells and modulates the immune response facilitating the spread of the tuberculosis disease. Here, we demonstrate that a previously uncharacterized secreted protein from Mtb, Rv1813c, manipulates the host metabolism by targeting mitochondria. When expressed in eukaryotic cells, the protein is delivered to the mitochondrial intermembrane space and promotes the enhancement of host ATP production by boosting the oxidative phosphorylation metabolic pathway. Furthermore, the release of cytochrome c from mitochondria, an early apoptotic event in response to short-term oxidative stress, is delayed in Rv1813c-expressing cells. This study reveals a novel class of mitochondria targeting effectors from Mtb that might participate in host cell metabolic reprogramming and apoptosis control during Mtb infections. IMPORTANCE In this article, using a combination of techniques (bioinformatics, structural biology, and cell biology), we identified and characterized a new class of effectors present only in intracellular mycobacteria. These proteins specifically target host cell mitochondria when ectopically expressed in cells. We showed that one member of this family (Rv1813c) affects mitochondria metabolism in a way that might twist the immune response. This effector also inhibits the cytochrome c exit from mitochondria, suggesting that it might alter normal host cell apoptotic capacities, one of the first defenses of immune cells against Mtb infection.

Structure-Based and Knowledge-Informed Design of B-Raf Inhibitors Devoid of Deleterious PXR Binding.

Dabrafenib is an anticancer drug currently used in the clinics, alone or in combination. However, dabrafenib was recently shown to potently activate the human nuclear receptor pregnane X receptor (PXR). PXR activation increases the clearance of various chemicals and drugs, including dabrafenib itself. It may also enhance cell proliferation and tumor aggressiveness. Therefore, there is a need for rational design of a potent protein kinase B-Raf inhibitor devoid of binding to the secondary target PXR and resisting rapid metabolism. By determining the crystal structure of dabrafenib bound to PXR and analyzing its mode of binding to both PXR and its primary target, B-Raf-V600E, we were able to derive new compounds with nanomolar activity against B-Raf and no detectable affinity for PXR. The crystal structure of B-Raf in complex with our lead compound revealed a subdomain swapping of the activation loop with potentially important functional implications for a prolonged inhibition of B-Raf-V600E.