The thermostable direct hemolysin of Vibrio parahaemolyticus is a pore-forming toxin

Abstract

The hemolytic mechanism of thermostable direct hemolysin (TDH), a possible virulence factor of Vibrio parahaemolyticus, was studied. We demonstrated that TDH acts as a "pore-forming toxin" in temperature-dependent and -independent steps. The first temperature-dependent step requires only about 1-2 min incubation at 37 degrees C and makes a "pore" with a functional diameter of approximately 2 nm. The pore size was deduced from the molecular diameter of the colloidal inhibitory polysaccharides. The formation of the pores on TDH-treated erythrocyte membranes was also demonstrated by electron microscopic examination. The second step, which is a temperature-independent lytic step, causes the erythrocytes to swell owing to a colloidal osmotic influx of water via the "pores" into cells, resulting in erythrocyte lysis (or rupture) owing to increased intracellular pressure.

Mechanisms of chloride secretion induced by thermostable direct haemolysin of Vibrio parahaemolyticus in human colonic tissue and a human intestinal epithelial cell line

“…TDH is a pore-forming toxin creating a functional pore size of c. 2 nm in target membranes [10]. Thus, there is the possibility that Cl À moves through TDH-formed pores.…”

“…It has been suggested that the haemolytic effect of TDH is initiated by binding to the erythrocyte surface and subsequent pore formation in the membrane, resulting in colloid osmotic lysis [10]. It was not known whether the binding of TDH to cell receptors had a signi®cant effect on Isc in the human colon.…”

Regulation of type III secretion system 1 gene expression inVibrio parahaemolyticusis dependent on interactions between ExsA, ExsC, and ExsD

“…5 Cell culture studies have shown that TDH is required to alter ion flux and to form pores in intestinal cell membranes. 11,12 Using a rabbit ileal loop model, Nishibuchi et al 13 demonstrated that fluid accumulation following infection with a tdh deletion strain was significantly reduced compared to the wildtype strain. Other studies showed that the pathogenicity of V. parahaemolyticus was also related to the adherence to human Vibrio parahaemolyticus exsA is the transcriptional regulator for type III secretion system 1 (T3ss1) while exsD blocks T3ss1 expression.…”

Diarrhea induced by infection of <I>Vibrio parahaemolyticus</I>

“…!for 10 min (14,15) and has hemolytic, cytotoxic, enterotoxic, mouse lethality and cardiotoxic activities (14). It is believed that Vp-TDH damages the erythrocyte membrane by acting as a pore-forming toxin, with the pores estimated at 2 nm in diameter (Vp-TDH also has the ability to lyse target eukaryotic cells by punching holes in the plasma membrane) (16).…”

“…Evidence suggests that Vp-TDH-induced hemolysis occurs in three sequential steps : 1) binding to the erythrocyte membrane, 2) formation of a transmembrane pore, and 3)disruption of the cell membrane (16). The N-terminal region is thought to be involved in the binding process, whereas the region near the C-terminal region has been implicated in post-binding activities (17).…”