Glutamate mediated metabolic neutralization mitigates propionate toxicity in intracellular Mycobacterium tuberculosis

Jae Jin Lee,Saki Raheem,Christopher P Lawson,Bo-Young Jeon,Sung-Ho Kang,Mark Odell,Jeongim Woo,Juhyeon Lim,Shengjia Gao,Hyungjin Eoh,Shin-Seok Kang

doi:10.1038/s41598-018-26950-z

Abstract

Metabolic networks in biological systems are interconnected, such that malfunctioning parts can be corrected by other parts within the network, a process termed adaptive metabolism. Unlike Bacillus Calmette-Guérin (BCG), Mycobacterium tuberculosis (Mtb) better manages its intracellular lifestyle by executing adaptive metabolism. Here, we used metabolomics and identified glutamate synthase (GltB/D) that converts glutamine to glutamate (Q → E) as a metabolic effort used to neutralize cytoplasmic pH that is acidified while consuming host propionate carbon through the methylcitrate cycle (MCC). Methylisocitrate lyase, the last step of the MCC, is intrinsically downregulated in BCG, leading to obstruction of carbon flux toward central carbon metabolism, accumulation of MCC intermediates, and interference with GltB/D mediated neutralizing activity against propionate toxicity. Indeed, vitamin B12 mediated bypass MCC and additional supplement of glutamate led to selectively correct the phenotypic attenuation in BCG and restore the adaptive capacity of BCG to the similar level of Mtb phenotype. Collectively, a defective crosstalk between MCC and Q → E contributes to attenuation of intracellular BCG. Furthermore, GltB/D inhibition enhances the level of propionate toxicity in Mtb. Thus, these findings revealed a new adaptive metabolism and propose GltB/D as a synergistic target to improve the antimicrobial outcomes of MCC inhibition in Mtb.

Highlights

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB), claimed 1.8 million human lives in 2016, the highest cause of human mortality among infectious diseases including AIDS1
Efficient coordination of the interaction between methylcitrate cycle (MCC) and Q → E activity is an essential component for Mtb’s intracellular lifestyle, this functional crosstalk is relatively inefficient in Bacillus Calmette-Guérin (BCG) metabolism that may contribute to intracellular phenotypic attenuation
Unlike H37Rv wild type M. tuberculosis (WT Mtb), whose in vitro growth is supported by a wide range of carbon species[28], BCG (Pasteur 1173P2) has a much narrower carbon source preference to support its in vitro growth

Summary

Introduction

Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB), claimed 1.8 million human lives in 2016, the highest cause of human mortality among infectious diseases including AIDS1. Mtb remodels its metabolic networks in order to assimilate new nutrients and, more importantly, to neutralize any adverse consequences that may occur during catalysis, processes collectively termed adaptive metabolism[6,7,8,9,10] This metabolic feature allows for maximum efficiency in the utilization of host nutrients and optimal virulence[11]. The RD1 locus of Mtb includes early secreted antigenic target (ESAT-6), secretion system-1 (ESX-1), and culture filtrate protein (CFP-10), all of which were known to play significant roles in Mtb virulence and interaction with host macrophages[21,22,23,24] These genetic defects in BCG have yet to fully explain its phenotypic attenuation in the host[14,25]. The discovery of functional interaction between MCC and Q → E identifies GltB/D as a new potential drug target whose inhibition mimics the bactericidal properties of Mtb’s MCC activity by maximizing the propionate toxicity

Methods

Results

Conclusion