The properties of Bacillus cereus hemolysin II pores depend on environmental conditions

Abstract

Hemolysin II (HlyII), one of several cytolytic proteins encoded by the opportunistic human pathogen Bacillus cereus, is a member of the family of oligomeric beta-barrel pore-forming toxins. This work has studied the pore-forming properties of HlyII using a number of biochemical and biophysical approaches. According to electron microscopy, HlyII protein interacts with liposomes to form ordered heptamer-like macromolecular assemblies with an inner pore diameter of 1.5-2 nm and an outer diameter of 6-8 nm. This is consistent with inner pore diameter obtained from osmotic protection assay. According to the 3D model obtained, seven HlyII monomers might form a pore, the outer size of which has been estimated to be slightly larger than by the other method, with an inner diameter changing from 1 to 4 nm along the channel length. The hemolysis rate has been found to be temperature-dependent, with an explicit lag at lower temperatures. Temperature jump experiments have indicated the pore structures formed at 37 degrees C and 4 degrees C to be different. The channels formed by HlyII are anion-selective in lipid bilayers and show a rising conductance as the salt concentration increases. The results presented show for the first time that at high salt concentration HlyII pores demonstrate voltage-induced gating observed at low negative potentials. Taken together we have found that the membrane-binding properties of hemolysin II as well as the properties of its pores strongly depend on environmental conditions. The study of the properties together with structural modeling allows a better understanding of channel functioning.

Iron Regulates Expression of Bacillus cereus Hemolysin II via Global Regulator Fur

“…In concert with these in vitro data, we showed that expression of HlyII in B. subtilis renders this organism virulent for the crustacean Daphnia magna (36) and leads to membrane damage in the alga Chara corallina (25); the role of HlyII in the virulence of B. thuringiensis in mice and insects was demonstrated by others (40). The toxic properties of HlyII rely on its ability to disrupt cellular and artificial membranes by pore formation (3). The prevalence of the hlyII genes among various B. cereus pathogenic strains is a significant indicator of their potential importance in virulence and pathogenesis (11).…”

“…Thus, it was no surprise that the overall expression profiles of hlyII and hlyII-lacZ were different but both hlyII-lacZ promoter activity and specific HlyII hemolytic activity were repressed 2-to 3-fold by 0.3 mM FeCl 3 . Variation of Fe concentrations in the range of 0.1 to 0.3 mM FeCl 3 did not affect the repression level.…”

InhA1, NprA, and HlyII as Candidates for Markers To Differentiate Pathogenic from NonpathogenicBacillus cereusStrains

“…InhA1, NprA, and HlyII may play a role in addition to the enterotoxins. InhA1 and NprA are proteases cleaving various membrane components (11), and HlyII has cytotoxic and hemolytic activities (2). These properties may allow the bacteria to gain access to deeper tissues and to disseminate.…”

“…HlyII hemolytic activity toward rabbit blood cells is over 15 times more potent than that of Staphylococcus alpha-toxin (48). It forms heptameric pores in synthetic lipid bilayers and is hemolytic and cytotoxic to various human cell lines (2,3). HlyII induces apoptosis in human and mouse macrophages and is strongly implicated in B. cereus virulence toward mice and insects (S. Tran, E. Guillemet, C. Clybouw, A. Moris, M. Gohar, D. Lereclus, and N. Ramarao, submitted for publication).…”

Bacterial white patch disease caused by Bacillus cereus, a new emerging disease in semi-intensive culture of Litopenaeus vannamei

“…Concerning with the adverse environmental conditions, the hly gene may be switched on and express the virulence factors. Andreeva et al (2007) supported that, optimum temperature for HlyII expression and action is between 15 and 28 °C could use this weapon in the crustacean gut.…”