Hemolysins are exotoxins produced by bacteria that cause lysis of red blood cells in vitro. Visualization of hemolysis of red blood cells in agar plates facilitates the categorization of some pathogenic bacteria such as Streptococcus and Staphylococcus. Although the lytic activity of some hemolysins on red blood cells may be important for nutrient acquisition or for causing certain conditions such as anemia, many hemolysin-producing pathogens do not cause significant lysis of red blood cells during infection. Although hemolysins are able to lyse red blood cells in vitro, the ability of hemolysins to target other cells, including white blood cells, often accounts for the effects of hemolysins in the host.
Most hemolysins are proteins, but others such as rhamnolipids are lipid biosurfactants.[1]
[edit] Function
Bacteria may use hemolysins as a way to obtain nutrients from host cells. For example, iron may be a limiting factor in the growth of various pathogenic bacteria.[2] Since free iron may generate damaging free radicals, free iron is typically maintained at low concentrations within the body. Red blood cells are rich in iron-containing heme. Lysis of these cells releases heme into the surroundings, allowing the bacteria to take up the free iron.
The regulation of gene expression of hemolysins (such as streptolysin S) is a system repressed in the presence of iron.[3] This ensures that hemolysin is produced only when needed.
Some hemolysins, such as listeriolysin O, allow bacteria to evade the immune system by escaping from phagosomes. Hemolysins may also mediate bacterial escape from host cells.
It is now believed that many clinically relevant fungi also produce hemolysins.[4]
[edit] 3D structure of hemolysin
Staphylococcus aureus alpha-Hemolysin forms a homo-heptameric beta-barrel in biological membranes (Protein Data Bank:7AHL).[5]
[edit] Examples
[edit] References
- ^ Stipcevic T, Piljac T, Isseroff RR (November 2005). "Di-rhamnolipid from Pseudomonas aeruginosa displays differential effects on human keratinocyte and fibroblast cultures". J. Dermatol. Sci. 40 (2): 141–3. doi:10.1016/j.jdermsci.2005.08.005. PMC 1592130. PMID 16199139. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1592130.
- ^ Sritharan M (July 2006). "Iron and bacterial virulence". Indian J Med Microbiol 24 (3): 163–4. PMID 16912433. http://www.ijmm.org/text.asp?2006/24/3/163/26987.
- ^ Griffiths BB, McClain O (1988). "The role of iron in the growth and hemolysin (Streptolysin S) production in Streptococcus pyogenes". J. Basic Microbiol. 28 (7): 427–36. doi:10.1002/jobm.3620280703. PMID 3065477.
- ^ Vesper SJ, Vesper MJ (2004). "Possible role of fungal hemolysins in sick building syndrome". Adv. Appl. Microbiol. 55: 191–213. doi:10.1016/S0065-2164(04)55007-4. PMID 15350795.
- ^ Song L, Hobaugh MR, Shustak C, Cheley S, Bayley H, Gouaux JE (December 1996). "Structure of staphylococcal alpha-hemolysin, a heptameric transmembrane pore". Science 274 (5294): 1859–66. doi:10.1126/science.274.5294.1859. PMID 8943190.
[edit] See also
[edit] External links
