Proteasomal Control of Cytokinin Synthesis Protects Mycobacterium tuberculosis against Nitric Oxide

Abstract

Summary One of several roles of the Mycobacterium tuberculosis proteasome is to defend against host-produced nitric oxide (NO), a free radical that can damage numerous biological macromolecules. Mutations that inactivate proteasomal degradation in Mycobacterium tuberculosis result in bacteria that are hypersensitive to NO and attenuated for growth in vivo, but it was not known why. To elucidate the link between proteasome function, NO-resistance, and pathogenesis, we screened for suppressors of NO hypersensitivity in a mycobacterial proteasome ATPase mutant and identified mutations in Rv1205. We determined that Rv1205 encodes a pupylated proteasome substrate. Rv1205 is a homologue of the plant enzyme LONELY GUY, which catalyzes the production of hormones called cytokinins. Remarkably, we report for the first time that an obligate human pathogen secretes several cytokinins. Finally, we determined that the Rv1205-dependent accumulation of cytokinin breakdown products is likely responsible for the sensitization of Mycobacterium tuberculosis proteasome-associated mutants to NO.

The Plant Hormone Cytokinin Confers Protection against Oxidative Stress in Mammalian Cells

“…Quite intriguingly and apart from the external application/addition of CKs to mammalian cells a recent finding on the regulation of LOG-like protein (CK-activating enzyme) by the animal pathogen M . tuberculosis [3] underscores the biological significance of CKs in animal/mammalian models of host-pathogen interactions [4]. As LOG-domain containing proteins are present in various pathogenic and non-pathogenic prokaryotic lineages [4] and thus points to the potential implications of CKs for infection by various important animal pathogens.…”

“…The CK signal is perceived by membrane-located sensor histidine kinases and transmitted through a two-component system (TCS) which is among the higher eukaryotes unique to plants [1, 2]. Besides plants, many plant-interacting microbes, such as various types of pathogenic and non-pathogenic bacteria, some fungi, nematodes and animal pathogens such as Mycobacterium tuberculosis have been shown to produce CK [3, 4]. In spite of their bright prospects for applied research, the presence of CKs, their signaling circuitry and their biological functions in mammalian cells are largely uncharacterized.…”

Prokaryotic Ubiquitin-Like Protein and Its Ligase/Deligase Enyzmes

“…Most progress in this direction has been made in Mycobacterium tuberculosis (Mtb) and its non-pathogenic, close relative Mycobacterium smegmatis (Msm). Mtb persistence inside host macrophages is supported by a functional PPS locus [43,44], which can at least in part be traced back to the prevention of nitric oxide (NO) toxicity for the pathogen by proteasomal degradation of an enzyme responsible for production of cytokinins [45]. Although the exact mechanism is not fully understood, the breakdown products of cytokinins together with the NO produced by the macrophage lead to strongly bacteriotoxic effects.…”

Tuberculosis: Hey There, Lonely Guy!

“…In this issue of Molecular Cell, Samanovic et al (2015) identify that the mycobacterial proteasomal substrate encoded by Rv1205, which appears to code for a homolog of the plant-like enzyme LONELY GUY, is responsible for proteasome-mediated nitric oxide resistance.…”

“…It has been presumed over the last decade that mycobacterial NO resistance was due to regulation of one-or, more likely, many-of the substrates of the mycobacterial proteasome-pupylation system (PPS) that make up the mycobacterial ''pupylOME'' (Watrous et al, 2010). In this issue of Molecular Cell, Darwin and colleagues (Samanovic et al, 2015) identify the mechanism by which the proteasome regulates NO resistance.…”