8-hemolysin

Staphylococcal a-hemolysin is another widely studied pore-forming toxin. It is used by infectious bacteria to perforate host animal cells by a mechanism that is distinct from that of gramicidin. Several aspects of the stmcture and function of this heptameric protein complex have been smdied. 

Aeromonas hydrophila is a bacterium that causes diarrheal diseases and deep wound infections. These complications arise due to pore formation in sensitive cells by the protein toxin aerolysin. Proteolytic processing of the 52-kD precursor proaerolysin (Figure 10.34) produces the toxic form of the protein, aerolysin. Like a-hemolysin, aerolysin monomers associate to form a heptameric transmembrane pore. Michael Parker and coworkers have proposed... 

FIGURE 10.33 The structure of the heptameric channel formed by o -hemolysin. Each of the seven subunits contributes a /3-sheet hairpin to the transmembrane channel. 

Proteolysis of this precursor yields the active form, aerolysiu, which is responsible for the pathogenic effects of the bacterium in deep wound infectious and diarrheal diseases. Like hemolysin, aerolysiu monomers associate to form heptameric membrane pores. The three /3-strands that contribute to the formation of the heptameric pore are shown in red. The N-terminal domain (residues 1-80, yellow) is a small lobe that protrudes from the rest of the protein. 

Song, L., Hobangh, M., Shnstak, C., et al., 1996. Structure of staphylococcal o -hemolysin, a heptameric transmembrane pore. Science 274 1859 -1866. 

In reconstitution experiments, the self-assembly of the pore-forming protein a-hemolysin of Staphylococcus aureus (aHL) [181-183] was examined in plain and S-layer-supported lipid bilayers. Staphylococcal aHL formed lytic pores when added to the lipid-exposed side of the DPhPC bilayer with or without an attached S-layer from B coagulans E38/vl. The assembly of aHL pores was slower at S-layer-supported compared to unsupported folded membranes. No assembly could be detected upon adding aHL monomers to the S-layer face of the composite membrane. Therefore, the intrinsic molecular sieving properties of the S-layer lattice did not allow passage of aHL monomers through the S-layer pores to the lipid bilayer [142]. 

The actions of proteins isolated from sea anemones, or other coelenterates, involve mechanisms different from those described for saponins. Thus, hemolysins from sea anemone R macrodactylus are capable of forming ion channels directly in membranes (98). The basic protein from S. helianthus also forms channels in black-lipid membranes. These channels are permeable to cations and show rectification (99). This ability of S. helianthus toxin III to form channels depends upon the nature of the host lipid membrane (100). Cytolysin S. helianthus binds to sphingomyelin and this substance may well serve as the binding site in cell membranes (101-106). 

Figure 5.4 Typical total ion chromatogram by pyrolysis MAB/Tof MS for deposition of 0.5 pi of suspension (about 50,000 cells). The cells were a thermostable direct hemolysin producing V. parahaemolyticus serotype 04 K12. Peak width at half maximum intensity is 20 scans ( 4 seconds).

The Forssman antigens17 may be regarded as heat-stable substances, which, when injected into rabbits, can evoke sheep-cell hemolysins. 

Baldwin TJ, Knutton S, Sellers L, Hernandez HA, Aitken A, Williams PH Enteroaggregative Escherichia coli strains secrete a heat-labile toxin antigenically related to E. coli hemolysin. Infect Immun 1992,60 2092-2095. 

An important virulence factor of bacteria is their ability to adhere to urinary epithelial cells by fimbriae, resulting in colonization of the urinary tract, bladder infections, and pyelonephritis. Other virulence factors include hemolysin, a cytotoxic protein produced by bacteria that lyses a wide range of cells... 

Lefkowitz, S.S. and Chiang, C.Y., Effects of certain abused drugs on hemolysin forming cells, Life ScL, 17, 1763, 1975. 

Korhonen, T. K., Valtonen, M. V., Parrkinen, J., Vaisanen-Rhen, V., Finne, J., Orskov, L, Svenson, S. B., and Makela, P. H. (1985). Serotypes, hemolysin production, and receptor recognition of Escherichia coli strains associated with neonatal sepsis and meningitis. Infect. Immun. 48,486-491. 

The prototype of a small pore-forming toxin is the S. aureus a-toxin, also called ct-hemolysin, that has been extensively investigated hy Bhakdi and coworkers. Monomers of ct-hemolysin (33 kDa) hind to the surface of erythrocytes, and after lateral diffusion within the lipid hilayer, seven monomers oligomerize to form pores in the cell membrane. The ct-hemolysin forms mushroom-shaped pores with an outer diameter of lOnm and an inner diameter of approximately 2.5 nm. Small molecules can pass through the pore and diffuse into/out of the cytosol, along with water. As a consequence of such movement, cell homeostasis is greatly disturbed and pushed into an unhealthy state. In animals, the a-hemolysin represents a major virulence factor of S. aureus which causes hemolysis as well as tissue destruction. ... 

The expression of the a-hemolysin pore protein from S. aureus inside the vesicle solved the energy and material limitations the reactor could sustain expression for up to four days. 

Bacterial pore-forming proteins, such as oc-hemolysin, secreted by Staphylococcus aureus can be modified so that pore formation is activated by chemical, biochemical, or physical triggers. Such hemolysins, when targeted to tumors, could increase tumor permeability, and hence susceptibility to various cytotoxic drugs (78). 

Squalene, squalane Phosvitin Phytic acid Phospholipids Spermidine Hyaluronic acid Sphingomyelin Biopolymer Fibronectin Spermine-bile acids Deacylated saponin a-Hemolysin... 

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