Vibrio Type III Effector VPA1380 Is Related to the Cysteine Protease Domain of Large Bacterial Toxins

Thomas Calder,Dor Salomon,Lisa N Kinch,Jessie Fernandez,Kim Orth,Nick V Grishin,Eric Cascales

doi:10.1371/journal.pone.0104387

Abstract

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium and one of the leading causes of food-borne gastroenteritis. Its genome harbors two Type III Secretion Systems (T3SS1 and T3SS2), but only T3SS2 is required for enterotoxicity seen in animal models. Effector proteins secreted from T3SS2 have been previously shown to promote colonization of the intestinal epithelium, invasion of host cells, and destruction of the epithelial monolayer. In this study, we identify VPA1380, a T3SS2 effector protein that is toxic when expressed in yeast. Bioinformatic analyses revealed that VPA1380 is highly similar to the inositol hexakisphosphate (IP6)-inducible cysteine protease domains of several large bacterial toxins. Mutations in conserved catalytic residues and residues in the putative IP6-binding pocket abolished toxicity in yeast. Furthermore, VPA1380 was not toxic in IP6 deficient yeast cells. Therefore, our findings suggest that VPA1380 is a cysteine protease that requires IP6 as an activator.

Highlights

Vibrio parahaemolyticus is a Gram-negative bacterium and one of the major etiological agents of acute gastroenteritis derived from eating raw or undercooked shellfish [1]
VPA1380 is a T3SS2 Effector While examining the genes within the T3SS2 pathogenicity island we identified vpa1380 as a putative T3SS2 effector
To confirm VPA1380 is secreted from T3SS2, we transformed V. parahaemolyticus strains with a plasmid containing vpa1380 fused to the catalytic region of the cyaA gene with vpa1380’s endogenous promoter

Summary

Introduction

Vibrio parahaemolyticus is a Gram-negative bacterium and one of the major etiological agents of acute gastroenteritis derived from eating raw or undercooked shellfish [1]. The genome sequence of the V. parahaemolyticus RIMD 2210633 clinical isolate revealed several virulence factors in pathogenicity islands [6]. These pathogenicity islands include two type III secretion systems (T3SS), T3SS1 and T3SS2 [7], and two type VI secretion systems (T6SS), T6SS1 and T6SS2 [8]. VopC constitutively activates Cdc through a deamidation reaction to promote invasion of the bacterium into non-phagocytic cells [13,18]. This data suggests bacterial invasion may play a role during infection

Methods

Results

Conclusion