Structural and functional analysis of the Klebsiella pneumoniae MazEF toxin-antitoxin system.

Chenglong Jin,Sung-Min Kang,Bong-Jin Lee,Do-Hee Kim

doi:10.1107/s2052252521000452

Abstract

Bacterial toxin-antitoxin (TA) systems correlate strongly with physiological processes in bacteria, such as growth arrest, survival and apoptosis. Here, the first crystal structure of a type II TA complex structure of Klebsiella pneumoniae at 2.3 Å resolution is presented. The K. pneumoniae MazEF complex consists of two MazEs and four MazFs in a heterohexameric assembly. It was estimated that MazEF forms a dodecamer with two heterohexameric MazEF complexes in solution, and a truncated complex exists in heterohexameric form. The MazE antitoxin interacts with the MazF toxin via two binding modes, namely, hydro-phobic and hydro-philic interactions. Compared with structural homologs, K. pneumoniae MazF shows distinct features in loops β1-β2, β3-β4 and β4-β5. It can be inferred that these three loops have the potential to represent the unique characteristics of MazF, especially various substrate recognition sites. In addition, K. pneumoniae MazF shows ribonuclease activity and the catalytic core of MazF lies in an RNA-binding pocket. Mutation experiments and cell-growth assays confirm Arg28 and Thr51 as critical residues for MazF ribonuclease activity. The findings shown here may contribute to the understanding of the bacterial MazEF TA system and the exploration of antimicrobial candidates to treat drug-resistant K. pneumoniae.

Highlights

Toxin–antitoxin (TA) systems were originally discovered as plasmid maintenance systems in almost all free-living bacteria, in which only daughter cells harboring the TA operon can survive (Yamaguchi et al, 2011)
The crystal structure of the MazEF complex from K. pneumoniae was determined at a resolution of 2.3 A
The asymmetric unit of the MazEF complex is composed of two MazE antitoxins and four MazF toxins in a heterohexameric assembly [Fig. 1(a)]

Summary

Introduction

Toxin–antitoxin (TA) systems were originally discovered as plasmid maintenance systems in almost all free-living bacteria, in which only daughter cells harboring the TA operon can survive (Yamaguchi et al, 2011). The transcription of the toxin gene is coupled with that of its cognate antitoxin gene, and the antitoxin blocks the toxicity of the toxin (Lobato-Marquez et al, 2016). Unfavorable circumstances, such as nutrient deficiency, antibiotic treatment, environmental stress, plasmid loss, bacteriophage infection, immune system attack, oxidative stress and high temperature, induce a decrease in antitoxin concentration, leading to increased levels of free toxin and in turn to growth arrest and eventually cell death (Kang et al, 2018). In type I TA systems, the antitoxin is an antisense RNA that forms base pairs with toxin mRNA and

Methods

Results

Conclusion