The ng_ζ1 toxin of the gonococcal epsilon/zeta toxin/antitoxin system drains precursors for cell wall synthesis

Abstract

Bacterial toxin–antitoxin complexes are emerging as key players modulating bacterial physiology as activation of toxins induces stasis or programmed cell death by interference with vital cellular processes. Zeta toxins, which are prevalent in many bacterial genomes, were shown to interfere with cell wall formation by perturbing peptidoglycan synthesis in Gram-positive bacteria. Here, we characterize the epsilon/zeta toxin–antitoxin (TA) homologue from the Gram-negative pathogen Neisseria gonorrhoeae termed ng_ɛ1 / ng_ζ1. Contrary to previously studied streptococcal epsilon/zeta TA systems, ng_ɛ1 has an epsilon-unrelated fold and ng_ζ1 displays broader substrate specificity and phosphorylates multiple UDP-activated sugars that are precursors of peptidoglycan and lipopolysaccharide synthesis. Moreover, the phosphorylation site is different from the streptococcal zeta toxins, resulting in a different interference with cell wall synthesis. This difference most likely reflects adaptation to the individual cell wall composition of Gram-negative and Gram-positive organisms but also the distinct involvement of cell wall components in virulence.

Toxin ζ Reduces the ATP and Modulates the Uridine Diphosphate-N-acetylglucosamine Pool

“…This is consistent with the affinity binding predictions that revealed relatively higher affinities for UNAG than for ATP (Table 1) and the decrease in vivo pool of the ATP pool upon toxin ζ expression [13]. Some of these features are also observed in a distantly related ζ -like toxin prevalent in Neisseria Gonorrhoeae plasmids (termed ng_ ζ 1) [49]. This new subclass of ζ -like toxin produces ADP in excess with respect to UNAG-P, and shows a catalytic efficiency ~8-fold higher for ATP than for UNAG [49].…”

“…Some of these features are also observed in a distantly related ζ -like toxin prevalent in Neisseria Gonorrhoeae plasmids (termed ng_ ζ 1) [49]. This new subclass of ζ -like toxin produces ADP in excess with respect to UNAG-P, and shows a catalytic efficiency ~8-fold higher for ATP than for UNAG [49]. Toxin ng_ ζ 1, however, phosphorylates the C4′-OH group of the N-acetylglucosamine moiety of UNAG rather than the C3′-OH group as shown for the Firmicutes toxins [18,49].…”

Identification and functional characterization of a bacterial homologue of Zeta toxin in Leishmania donovani

“…However, in the presence of zeta toxin, UNAG gets phosphorylated to UNAG-3P via ATP hydrolysis, which then binds to MurA and blocks its catalytic activity. Intriguingly, zeta toxin from N. gonorrhoeae phosphorylates the multiple UDP-activated sugar substrates, making them unavailable for binding to MurA, MurB, MurC, leading to abrogated cell wall synthesis [23]. Remarkably, based on environmental condition and dose of zeta toxin, cells may either undergo postsegregational killing or cell stasis [21,22].…”

A Systematic Overview of Type II and III Toxin-Antitoxin Systems with a Focus on Druggability

“…In exploiting bacterial toxins to induce cell killing, the induction of persistence should be avoided. Zeta toxins cause cell wall autolysis by substantially perturbing peptidoglycan synthesis [38,39,40], and bacterial mRNA endonuclease MazF toxin is suggested to be involved in programmed cell death. The programmed cell death induced by the toxins in TA systems is essential for therapeutic strategies [58,59], although controversy persists in the recent literature.…”

“…There are also other attractive possibilities, such as the antimicrobial agents involved in zeta-epsilon systems, which use synthetic peptides and small compounds. Liberated zeta toxin can block peptidoglycan synthesis followed by cell wall autolysis [38,39,40]. In addition, the human intestinal microbiota contains many organisms that possess type III TA systems, which are currently attracting attention because of their relevance in various human diseases, such as obesity, inflammatory and metabolic diseases and gastrointestinal and colon cancer, although type III systems do not necessarily cause these diseases [14,41,42,43,44,45].…”