Characterization of a toxin-antitoxin system in Mycobacterium tuberculosis suggests neutralization by phosphorylation as the antitoxicity mechanism

Xia Yu,Xiaopan Gao,Hairong Huang,Justyna Aleksandra Wojdyla,Xujian Mao,Sheng Cui,Yi-Cheng Sun,Han Yin,Bo Qin,Meitian Wang,Kaixiang Zhu

doi:10.1038/s42003-020-0941-1

Abstract

Mycobacterium tuberculosis (Mtb) encodes an exceptionally large number of toxin-antitoxin (TA) systems, supporting the hypothesis that TA systems are involved in pathogenesis. We characterized the putative Mtb Rv1044-Rv1045 TA locus structurally and functionally, demonstrating that it constitutes a bona fide TA system but adopts a previously unobserved antitoxicity mechanism involving phosphorylation of the toxin. While Rv1045 encodes the guanylyltransferase TglT functioning as a toxin, Rv1044 encodes the novel atypical serine protein kinase TakA, which specifically phosphorylates the cognate toxin at residue S78, thereby neutralizing its toxicity. In contrast to previous predictions, we found that Rv1044-Rv1045 does not belong to the type IV TA family because TglT and TakA interact with each other as substrate and kinase, suggesting an unusual type of TA system. Protein homology analysis suggests that other COG5340-DUF1814 protein pairs, two highly associated but uncharacterized protein families widespread in prokaryotes, might share this unusual antitoxicity mechanism.

Highlights

Mycobacterium tuberculosis (Mtb) encodes an exceptionally large number of toxin-antitoxin (TA) systems, supporting the hypothesis that TA systems are involved in pathogenesis
Deep and colleagues reported that the VapBC11 TA system is essential for establishing Mtb infection in vivo, providing an example of the TA system contributing to Mtb virulence[3]
While some studies contradict the involvement of TA systems in persister cells formation in E. coli[4,5,6,7,8], S. aureus[9] and S. enterica[10], there is evidence supporting the link between TA systems and persister cell formation in other bacteria[11,12,13,14,15]

Summary

Introduction

Mycobacterium tuberculosis (Mtb) encodes an exceptionally large number of toxin-antitoxin (TA) systems, supporting the hypothesis that TA systems are involved in pathogenesis. We characterized structurally and functionally Rv1044Rv1045 system, a putative type IV TA system from Mtb. We found that while Rv1045 encodes the guanylyltransferase TglT (unusual type guanylyltransferase-like toxin), which arrests bacterial growth, Rv1044 encodes the atypical protein kinase TakA (unusual type of atypical kinase antitoxin), which neutralizes the activity of TglT via phosphorylation. TglT- FLAG and TakA-Myc were co-expressed in BL21 cells and the expression of both proteins was detectable by western blotting (Fig. 1d).

Results

Conclusion