Analysis of the Zonula occludens Toxin Found in the Genome of the Chilean Non-toxigenic Vibrio parahaemolyticus Strain PMC53.7

Abstract

Vibrio parahaemolyticus non-toxigenic strains are responsible for about 10% of acute gastroenteritis associated with this species, suggesting they harbor unique virulence factors. Zonula occludens toxin (Zot), firstly described in Vibrio cholerae, is a secreted toxin that increases intestinal permeability. Recently, we identified Zot-encoding genes in the genomes of highly cytotoxic Chilean V. parahaemolyticus strains, including the non-toxigenic clinical strain PMC53.7. To gain insights into a possible role of Zot in V. parahaemolyticus, we analyzed whether it could be responsible for cytotoxicity. However, we observed a barely positive correlation between Caco-2 cell membrane damage and Zot mRNA expression during PMC53.7 infection and non-cytotoxicity induction in response to purified PMC53.7-Zot. Unusually, we observed a particular actin disturbance on cells infected with PMC53.7. Based on this observation, we decided to compare the sequence of PMC53.7-Zot with Zot of human pathogenic species such as V. cholerae, Campylobacter concisus, Neisseria meningitidis, and other V. parahaemolyticus strains, using computational tools. The PMC53.7-Zot was compared with other toxins and identified as an endotoxin with conserved motifs in the N-terminus and a variable C-terminal region and without FCIGRL peptide. Notably, the C-terminal diversity among Zots meant that not all of them could be identified as toxins. Structurally, PMC53.7-Zot was modeled as a transmembrane protein. Our results suggested that it has partial 3D structure similarity with V. cholerae-Zot. Probably, the PMC53.7-Zot would affect the actin cytoskeletal, but, in the absence of FCIGRL, the mechanisms of actions must be elucidated.

Expression of putative effectors of different Xylella fastidiosa subspecies/strains reveals recognition and defense activation in various model plants

“…Zot proteins have been associated with high cytotoxicity before (Pérez-Reytor et al, 2018), though this is not always the case. For instance, in Vibrio parahaemolyticus, "Zot" expression did not positively correlate with cytotoxicity, rather than with an actin disturbance on infected cells (Pérez-Reytor et al, 2020). Xf putative "Zot" proteins studied here appear not to correlate to cytotoxic effects.…”

Use of Short-Chain Fatty Acids for the Recovery of the Intestinal Epithelial Barrier Affected by Bacterial Toxins

“…Zot-type toxins have also been found in Vibrio parahaemolyticus and Vibrio vulnificus (Castillo et al, 2018a,b;Pérez-Reytor et al, 2018), both human pathogens. According to our recent studies, Zot would be associated with the actin cytoskeletal disturbances observed in Caco-2 cells after infection with a non-toxigenic strain of V. parahaemolyticus (Pérez-Reytor et al, 2020). On the other hand, it has been hypothesized that C. concisus disrupts gastrointestinal epithelium, driving a dysregulated immune response that results in chronic inflammation in the intestine (Mahendran et al, 2011;Zhang et al, 2014;O'Brien, 2017).…”

The Secretome of Vibrio cholerae

“…Accessory cholera enterotoxin (Ace -VC1459) and zonula occludens toxin (Zot -VC1458) are accessory toxins that are both encoded near the CT genes on the CTXφ phage [136,137]. Zot leads to the disruption of the tight junctions between intestinal epithelial cells, an important structure in the intestinal permeability [138,139]. It is translocated and anchored in the outer membrane and has two functional domains.…”

“…Thus, Zot does not employ a conventional secretion system for its release into the extracellular milieu. Regarding Ace, it leads to fluid secretion in rabbit ileal loop model by unbalancing calcium secretion and the secretion mechanism has not been determined yet [138].…”