Rapid growth inhibitory activity of a YafQ-family endonuclease toxin of the Helicobacter pylori tfs4 integrative and conjugative element

Abstract

Prokaryotic and archaeal chromosomes encode a diversity of toxin–antitoxin (TA) systems that contribute to a variety of stress-induced cellular processes in addition to stability and maintenance of mobile elements. Here, we find DinJ-YafQ family TA systems to be broadly distributed amongst diverse phyla, consistent with other ParE/RelE superfamily TAs, but more unusually occurring as a multiplicity of species-specific subtypes. In the gastric pathogen Helicobacter pylori we identify six distinct subtypes, of which three are predominantly associated with the mobilome, including the disease-associated integrative and conjugative element (ICE), tfs4. Whereas, the ICE-encoded proteins have characteristic features of DinJ-YafQ family Type II TA systems in general, the toxin component is distinguished by a broad metal-ion-dependent endonuclease activity with specificity for both RNA and DNA. We show that the remarkably rapid growth inhibitory activity of the ICE toxin is a correlate of a C-terminal lysine doublet which likely augments catalytic activity by increasing the positive electrostatic potential in the vicinity of the conserved active site. Our collective results reveal a structural feature of an ICE TA toxin that influences substrate catalysis and toxin function which may be relevant to specific TA-mediated responses in diverse genera of bacteria.

A novel double-ribonuclease toxin-antitoxin system linked to the stress response and survival of Acidovorax citrulli

“…Total RNA from the A. citrulli model strain AAC00-1 was isolated using the RNApure Bacteria Kit (CWBIO, Beijing, China), while individual mRNAs of the trpA , Aave_1720 , Aave_1719 , ompA , and atpE genes were prepared by in vitro transcription using the T7 RiboMAX Express Large Scale RNA Production System (Promega, WI, USA). The RNase assay itself was conducted as described previously ( 44 ) with a few minor changes. The reaction mixture contained either 2 µg total RNA or 1 µg individual mRNA, 50 mM Tris-HCl (pH 8.0), 150 mM NaCl, and the appropriate quantity of purified Aave_1720 (8.87–67.5 pmol) or Aave_1719 (10–300 pmol) protein.…”

Effect of Divalent Metal Ions on the Ribonuclease Activity of the Toxin Molecule HP0894 from Helicobacter pylori

“…In previous studies we elucidated the structure and function of two Type II TA systems from H. pylori, namely HP0892-HP0893 and HP0894-HP0895. In both systems, HP0892 and HP0894 act as toxins that form complexes with the antitoxins HP0893 and HP0895, respectively [15,16,20,31]. HP0892 is a homologue of HP0894 with 54% amino acid identity.…”

Toxin-Antitoxin Systems - A New Player in Morphological Transformation of Antibiotic-Exposed Helicobacter pylori?

“…To date, five type II TA systems of H. pylori have been identified. These include chromosomally encoded HP0892-HP0893 ( Han et al., 2013 ), HP0894-HP0895 ( Han et al., 2011 ), HP0315-HP0316 ( Kwon et al., 2012 ), and HP0967-HP0968 ( Cárdenas-Mondragón et al., 2016 ), and the newly identified TfiT-TfiA ( Boampong et al., 2020 ), which is encoded on mobile genetic fragments. The expression of toxins belonging to the above modules arrest the growth of bacterial producers and cause the reduction of their number (expressed in CFU/mL).…”