Chaperone addiction of toxin–antitoxin systems

Patricia Bordes,Ambre Julie Sala,Pierre Genevaux,Nawel Slama,Valérie Guillet,Pauline Texier,Lionel Mourey,Sara Ayala,Anne-Marie Cirinesi

doi:10.1038/ncomms13339

Abstract

Bacterial toxin–antitoxin (TA) systems, in which a labile antitoxin binds and inhibits the toxin, can promote adaptation and persistence by modulating bacterial growth in response to stress. Some atypical TA systems, known as tripartite toxin–antitoxin–chaperone (TAC) modules, include a molecular chaperone that facilitates folding and protects the antitoxin from degradation. Here we use a TAC module from Mycobacterium tuberculosis as a model to investigate the molecular mechanisms by which classical TAs can become ‘chaperone-addicted'. The chaperone specifically binds the antitoxin at a short carboxy-terminal sequence (chaperone addiction sequence, ChAD) that is not present in chaperone-independent antitoxins. In the absence of chaperone, the ChAD sequence destabilizes the antitoxin, thus preventing toxin inhibition. Chaperone–ChAD pairs can be transferred to classical TA systems or to unrelated proteins and render them chaperone-dependent. This mechanism might be used to optimize the expression and folding of heterologous proteins in bacterial hosts for biotechnological or medical purposes.

Highlights

Bacterial toxin–antitoxin (TA) systems, in which a labile antitoxin binds and inhibits the toxin, can promote adaptation and persistence by modulating bacterial growth in response to stress
We show that TAC antitoxins possess a short chaperone addiction sequence, named chaperone addition (ChAD), at their carboxy-terminal end, which efficiently prevents antitoxin folding and recruits the SecBTA chaperone
We found that B23% of luciferase and 91% of green fluorescent protein (GFP) were soluble in the absence of grafted ChAD sequence (Fig. 2c,d), which is coherent with the previous work using a similar in vitro system with luciferase[18]

Summary

Introduction

Bacterial toxin–antitoxin (TA) systems, in which a labile antitoxin binds and inhibits the toxin, can promote adaptation and persistence by modulating bacterial growth in response to stress. Some atypical TA systems, known as tripartite toxin–antitoxin–chaperone (TAC) modules, include a molecular chaperone that facilitates folding and protects the antitoxin from degradation. Chaperone–ChAD pairs can be transferred to classical TA systems or to unrelated proteins and render them chaperone-dependent This mechanism might be used to optimize the expression and folding of heterologous proteins in bacterial hosts for biotechnological or medical purposes. The TAC system of the major human pathogen Mycobacterium tuberculosis is the best characterized[4,10,12] It is encoded by three genes organized in an operon, Rv1955-Rv1956Rv1957, respectively, encoding the TA pair (Mtb-HigB1 and Mtb-HigA1) and the Mtb-SecBTA chaperone[10,12]. Grafting the ChAD sequence of Mtb-HigA1 to unrelated recombinant proteins or to chaperone-independent antitoxins of classical two-component TA systems renders them chaperone-dependent, indicating that chaperone addiction is transferable

Methods

Results

Conclusion