Summary: Leukocidin/Hemolysin toxin family
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Hemolysin Edit Wikipedia article
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Hemolysins (UK spelling: haemolysins) are certain proteins and lipids that cause lysis of red blood cells by damaging their cell membrane. Although the lytic activity of some microbial 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 during infection.
Many bacteria produce hemolysins that can be detected in the laboratory. It is now believed that many clinically relevant fungi also produce hemolysins. Hemolysins can be identified by their ability to lyse red blood cells in vitro.
Not only are the erythrocytes affected by hemolysins, but there are also some effects among other blood cells, such as leucocytes (white blood cells). Escherichia coli hemolysin is potentially cytotoxic to monocytes, lymphocytes and macrophages, leading them to autolysis and death.
Visualization of hemolysis (UK: haemolysis) of red blood cells in agar plates facilitates the categorization of Streptococcus.
In the next image we can see the process of hemolysis by a Streptococcus:
 Pore formation
Due to the importance of hemolysins and the formation of pores, this part looks forward to enhance some more aspects of the process. Many hemolysins are pore-forming toxins (PFT) which is capable to cause the lysis of erythrocytes, leukocytes and platelets by producing pores on the cytoplasmic membrane.
But, in which way does this kind of protein carry out this process?
Hemolysin is normally secreted by the bacteria in a water-resoluble way. These monomers diffuse to the target cells and are attached to them by specific receivers. After this is already done, they oligomerize creating ring-shaped heptamer complexes.
Hemolysin can be segregated by many different kinds of bacteria such as Staphylococcus aureus, Escherichia coli or Vibrio parahemolyticus among other pathogens. We can take a look at the bacterium Staphylococcus aureus to study more precisely the formation of this pores. Staphylococcus aureus is a pathogen which causes many infectious diseases such as pneumonia and sepsis. This ring-shaped complex we’ll take a look at, is called staphylococcal alpha-hemolysin pore. In nature, what happens with these pathogens is that in its fight for resources, bacterium Staphylococcus aureus secretes alpha-hemolysin monomers that bind to the outer membrane of susceptible cells. Upon binding, the monomers oligomerize to form a water-filled transmembrane channel that facilitates uncontrolled permeation of water, ions, and small organic molecules. Rapid discharge of vital molecules, such as ATP, dissipation of the membrane potential and ionic gradients, and irreversible osmotic swelling leading to the cell wall rupture (lysis), can cause death of the host cell.
This pore consists of seven alpha-hemolysin subunits, which represent the major cytotoxic agent which is freed by this kind of bacterium. These subunits are attached the way we’ve already explained to the target cells and extend the lipid bilayer forming the pore structures. These pores in the cellular membrane will eventually end up causing cell death, since it allows the exchange of monovalent ions which would cause the DNA fragmentation.
Some hemolysins damage the erythrocyte membrane by cleaving the phospholipids in the membrane.
 Staphylococcus aureus hemolysins
Secreted by Staphylococcus aureus, this toxin causes cell death by binding with the outer membrane, with subsequent oligomerization of the toxin monomer and water-filled channels. These are responsible for osmotic phenomena, cell depolarization and loss of vital molecules (v.gr. ATP) leading to its demise.
Upon investigating sheep erythrocytes, its toxic mechanism was discovered to be the hydrolysis of a specific membrane lipid, sphingomyelin, which accounts for 50% of the cell’s membrane. This degradation was followed by a noticeable rise of phosphoryl choline due to the release of organic phosphorus from sphingomyelin and ultimately caused cell lysis.
Unlike beta hemolysin, it has a higher affinity for phosphocholines with short saturated acyl chains, especially if they have a conical form whereas cylindrical lipids (e.g. sphingomyelin) hinder its activity. The lytic process, most commonly seen in leucocytes, is caused by pore formation induced by an oligomerized octamer that organizes in a ring structure. Once the prepore is formed, a more stable one ensues, named β-barrel. In this final part, the octamer binds with phosphatidylcholine.
The structure of several hemolysins has been solved by X-ray crystallography in the soluble and pore-forming conformations. For example, α-hemolysin of Staphylococcus aureus forms a homo-heptameric β-barrel in biological membranes. The Vibrio cholerae cytolysin also forms a heptameric pore, however Staphylococcus aureus γ-hemolysin forms a pore which is octomeric.
Thanks to latest research on the field of hemolysin's structure, we do know that the structure of the Staphylococcus aureus α-hemolysin pore has been determined to 1.9 Å resolution. Contained within the mushroom-shaped homo-oligomeric heptamer is a solvent-filled channel, 100 Å in length, that runs along the sevenfold axis and ranges from 14 Å to 46 Å in diameter. Furthermore, the structure proves the heptameric subunit stoichiometry of the α-hemolysin oligomer, shows that a glycine-rich and solvent-exposed region of a water-soluble protein can self-assemble to form a transmembrane pore of defined structure, and provides insight into the principles of membrane interaction and transport activity of β barrel pore-forming toxins.
The structure of the detergent-solubilized heptamer has been determined by X-ray crystallography to 1.9 Å resolution. The heptamer has a mushroom-like shape and measures up to 100 Å in diameter and 100 Å in height. Spanning the length of the molecule and coincident with the molecular sevenfold axis is a water-filled channel that ranges in diameter from 16 to 46 Å. A 14 strand antiparallel β barrel. On the exterior of the β barrel there is a hydrophobic belt approximately 30 Å in width that provides a surface complementary to the nonpolar portion of the lipid bilayer. The interfaces are composed of both salt-links and hydrogen bonds, as well as hydrophobic interactions, and these contacts provide a molecular stability for the heptamer in SDS solutions even up to 65°C.
 Role during infection
Hemolysins are thought to be responsible for many events in host cells. For example, iron may be a limiting factor in the growth of various pathogenic bacteria. 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. But not only is hemolysin related to bacteria in this way but in some others.
As mentioned before, hemolysin is a potential virulence factor produced by microorganisms which can put human’s health at risk. Despite causing some severe pathologies, lots of cases of hemolysis do not suppose a health hazard. But the fact that hemolysins (produced by pathogenic microorganisms during infections) are combined with other virulence factors may threaten human’s life to a greater extent.
The main consequence of hemolysis is hemolytic anemia, condition that involves the destruction of erythrocytes and their later removal from the bloodstream, earlier than expected in a normal situation. As the bone marrow cannot make erythrocytes fast enough to meet the body’s needs, oxygen do not arrive to body tissues properly. Consequently, some symptoms may appear such as fatigue, pain, arrhythmias, an enlarged heart or even heart failure, among others.
Depending on the type of hemolysin and the microorganism that produces it, manifestation of symptoms and diseases may differ from one case to the other:
- Alpha-hemolysin from uropathogenic E. coli produces extra intestinal infections and can cause cystitis, pyelonephritis and septicemia. Alpha-hemolysin from Staphylococcus aureus can cause severe diseases, such as pneumonia.
- Aerolysin from Aeromonas sobria infects the intestinal tract, but it might also cause septicemia and meningitis.
(Both hemolysins mentioned above are synthetized by extracellular bacteria, which infect specific tissue surfaces.)
- Listeriolysin from Listeria monocytogenes (a facultative intracellular bacterium which thrives within host cells, mainly macrophages and monocytes) causes the degradation of phagosomes membranes, but they are not a potential danger for the cell’s plasmatic membrane.
Hemolysins have proved to be a damaging factor for vital organs, through the activity of Staphylococcus aureus. S.aureus is a dangerous pathogen that may lead cells to necrotizing infections usually recognized by a massive inflammatory response leading to tissue damage or even tissue destruction. There is a clear example of this: the pneumonia produced by S.aureus. In this case, it's been proved that alpha- hemolysin takes part in inducing necrotic pulmonary injury by the use of the NLRP3 inflammasome, which is responsible for inflammatory processes and of pyroptosis. Pneumonia caused by S.aureus is a common disease in some areas and that's the reason why there have been so many studies in the field of immunology in order to find some new farmacs to cure easily or prevent this kind of pneumonia. At the moment apiegnin and beta-cyclodextrin are thought to alleviate S.aureus pneumonia whereas the antibodies of anti alpha-hemlysin are thought to give protection.
Further findings show that the main virulence factor of S. aureus, the pore-forming toxin α-hemolysin (Hla), is the secreted factor responsible for the activation of an alternative autophagic pathway. It's been demonstrated that this autophagic response is inhibited by artificially elevating the intracellular levels of cAMP. This process is also mediated by the exchange factors RAPGEF3 and RAP2B.
Another interesting point is that pretreatment of leukocytes with doses of alpha-hemolysin at which nearly 80% of the cells survived decreased the ability of the cells to phagocytize bacteria and particles and to undergo chemotaxis. Premature activation of leukocytes and inhibition of phagocytosis and chemotaxis by alpha-hemolysin, if they occur in vivo, would greatly enhance the survival of an E. coli attack.
 Regulation of gene expression
The regulation of gene expression of hemolysins (such as streptolysin S) is a system repressed in the presence of iron. This ensures that hemolysin is produced only when needed. The regulation of the production of hemolysin in S.aureus(expression of hemolysin) is now possible due to in-vitro mutations which are related to serine/threonine kinase and phosphatase.
As hemolysins are produced by pathogenic organisms, the main treatment is the intake of antibiotics specific to the pathogen that have caused the infection. Moreover, some hemolysins may be neutralized by the action of anti-hemolysin antibodies, preventing a longer and more dangerous effect of hemolysis within the body.
When blood cells are being destroyed too fast, extra folic acid and iron supplements may be given or, in case of emergencies, a blood transfusion. In rare cases, the spleen must be removed because it filters blood and removes from bloodstream death or damaged cells, worsening the lack of erythrocytes.
The hemolysin TDH, or Thermoestable Direct Hemolysin, is now being studied in the field of oncology. It's now said that Thermostable Direct Hemolysin (TDH), produced by Vibrio parahaemolyticus, regulates cell proliferation in colon carcinoma cells. TDH induces Ca2+ influx from an extracellular environment accompanied by protein kinase C phosphorylation. Activated protein kinase C inhibits the tyrosine kinase activity of epidermal growth factor receptor (EGFR), the rational target of anti-colorectal cancer therapy.
α-hemolysin has been utilized to conduct nanopore sequencing of DNA.
 See also
- 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.
- 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.
- Chalmeau J, Monina N, Shin J, Vieu C, Noireaux V (January 2011). "α-Hemolysin pore formation into a supported phospholipid bilayer using cell-free expression". Biochim. Biophys. Acta 1808 (1): 271–8. doi:10.1016/j.bbamem.2010.07.027. PMID 20692229.
- Bhakdi S, Mackman N, Menestrina G, Gray L, Hugo F, Seeger W, Holland IB (June 1988). "The hemolysin of Escherichia coli". Eur. J. Epidemiol. 4 (2): 135–43. doi:10.1007/BF00144740. PMID 3042445.
- Thompson JR, Cronin B, Bayley H, Wallace MI (December 2011). "Rapid assembly of a multimeric membrane protein pore". Biophys. J. 101 (11): 2679–83. doi:10.1016/j.bpj.2011.09.054. PMID 22261056.
- McGillivray DJ, Heinrich F, Valincius G, Ignatjev I, Vanderah DJ, Lösche M, Kasianowicz JJ. "Membrane Association of α-Hemolysin: Proteins Functionally Reconstituted in tBLMs". Carnegie Mellon University.
- Maheswaran SK, Lindorfer RK (November 1967). "Staphylococcal beta-hemolysin. II. Phospholipase C activity of purified beta-hemolysin". J. Bacteriol. 94 (5): 1313–9. PMC 276826. PMID 4964474.
- Dalla Serra M, Coraiola M, Viero G, Comai M, Potrich C, Ferreras M, Baba-Moussa L, Colin DA, Menestrina G, Bhakdi S, Prévost G (2005). "Staphylococcus aureus bicomponent gamma-hemolysins, HlgA, HlgB, and HlgC, can form mixed pores containing all components". J Chem Inf Model 45 (6): 1539–45. doi:10.1021/ci050175y. PMID 16309251.
- 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.
- PDB 3o44; De S, Olson R (May 2011). "Crystal structure of the Vibrio cholerae cytolysin heptamer reveals common features among disparate pore-forming toxins". Proc. Natl. Acad. Sci. U.S.A. 108 (18): 7385–90. doi:10.1073/pnas.1017442108. PMC 3088620. PMID 21502531.
- PDB 3b07; Yamashita K, Kawai Y, Tanaka Y, Hirano N, Kaneko J, Tomita N, Ohta M, Kamio Y, Yao M, Tanaka I (October 2011). "Crystal structure of the octameric pore of staphylococcal γ-hemolysin reveals the β-barrel pore formation mechanism by two components". Proc. Natl. Acad. Sci. U.S.A. 108 (42): 17314–9. doi:10.1073/pnas.1110402108. PMC 3198349. PMID 21969538.
- Gouaux E (1998). "α-Hemolysin from Staphylococcus aureus: an archetype of β-barrel, channel-forming toxins". J. Struct. Biol. 121 (2): 110–22. doi:10.1006/jsbi.1998.3959. PMID 9615434.
- Sritharan M (July 2006). "Iron and bacterial virulence". Indian J Med Microbiol 24 (3): 163–4. PMID 16912433.
- "What Is Hemolytic Anemia? - NHLBI, NIH". United States National Institutes of Health. 2011-04-01. Retrieved 2012-11-24.
- Kebaier C, Chamberland RR, Allen IC, Gao X, Broglie PM, Hall JD, Jania C, Doerschuk CM, Tilley SL, Duncan JA (March 2012). "Staphylococcus aureus α-hemolysin mediates virulence in a murine model of severe pneumonia through activation of the NLRP3 inflammasome". J. Infect. Dis. 205 (5): 807–17. doi:10.1093/infdis/jir846. PMID 22279123.
- Dong J, Qiu J, Wang J, Li H, Dai X, Zhang Y, Wang X, Tan W, Niu X, Deng X, Zhao S (October 2012). "Apigenin alleviates the symptoms of Staphylococcus aureus pneumonia by inhibiting the production of alpha-hemolysin". FEMS Microbiol. Lett. doi:10.1111/1574-6968.12040. PMID 23113475.
- Mestre MB, Colombo MI (October 2012). "Staphylococcus aureus promotes autophagy by decreasing intracellular cAMP levels". Autophagy 8 (12). PMID 23047465.
- Cavalieri SJ, Snyder IS (September 1982). "Effect of Escherichia coli alpha-hemolysin on human peripheral leukocyte function in vitro". Infect. Immun. 37 (3): 966–74. PMC 347633. PMID 6752033.
- 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.
- Burnside K, Lembo A, de Los Reyes M, Iliuk A, Binhtran NT, Connelly JE, Lin WJ, Schmidt BZ, Richardson AR, Fang FC, Tao WA, Rajagopal L (2010). "Regulation of hemolysin expression and virulence of Staphylococcus aureus by a serine/threonine kinase and phosphatase". PLoS ONE 5 (6): e11071. doi:10.1371/journal.pone.0011071. PMC 2884019. PMID 20552019.
- Ragle BE, Bubeck Wardenburg J (July 2009). "Anti-alpha-hemolysin monoclonal antibodies mediate protection against Staphylococcus aureus pneumonia". Infect. Immun. 77 (7): 2712–8. doi:10.1128/IAI.00115-09. PMC 2708543. PMID 19380475.
- Karmakar P, Chakrabarti MK (July 2012). "Thermostable direct hemolysin diminishes tyrosine phosphorylation of epidermal growth factor receptor through protein kinase C dependent mechanism". Biochim. Biophys. Acta 1820 (7): 1073–80. doi:10.1016/j.bbagen.2012.04.011. PMID 22543197.
- Hemolysins at the US National Library of Medicine Medical Subject Headings (MeSH)
- Hemolysin at eMedicine Dictionary
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Leukocidin/Hemolysin toxin family Provide feedback
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This tab holds annotation information from the InterPro database.
InterPro entry IPR001340
Staphylococcus aureus is a Gram-positive coccus that grows in clusters or pairs, and is the major cause of nosocomial infections due to its multiple antibiotic resistant nature. Patients who are immuno-compromised (e.g., those suffering from third degree burns or chronic illness) are at risk from deep staphylococcal infections, such as osteomyelitis and pneumonia. Most skin infections are also caused by this bacterium [PUBMED:9350200].
Many virulence mechanisms are employed by Staphylococci to induce pathogenesis: these can include polysaccharide capsules and exotoxins [PUBMED:9350200]. Examples of the latter are bi-component toxins, which involve the synergistic combination of an "S" and an "F" component [PUBMED:9804914]. These undergo conformational changes in their protein structure and form oligomeric pores in the target cell membrane upon recognition of certain host receptors. The main cells targeted are polymorphonuclear cells, monocytes, erythrocytes and macrophages. Examples of this protein family include: leucocidin, gamma-haemolysin and alpha-haemolysin.
Recently, the crystal structure of the S. aureus leucocidin "F" component (LukF) has been determined to 1.9A resolution [PUBMED:10048924]. This structure, which comprises a central 3-strand beta-sheet, with an N-terminal "latch", clarified the mechanism of virulence in the bi-component toxin. Further work using a different form of the leucocidin (LukF-PV) has suggested that it may be a representative fold for water-soluble transmembrane toxins [PUBMED:10368297].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||extracellular region (GO:0005576)|
|Biological process||cytolysis in other organism (GO:0051715)|
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|Number in seed:||19|
|Number in full:||1628|
|Average length of the domain:||237.50 aa|
|Average identity of full alignment:||36 %|
|Average coverage of the sequence by the domain:||70.82 %|
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build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||7|
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Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.
If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.
For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
You can use the tree controls to manipulate how the interactive tree is displayed:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
- select a sub-tree or a set of species within the tree and view them graphically or as an alignment
- save a plain text representation of the tree
Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
There are 2 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Leukocidin domain has been found. There are 102 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
Loading structure mapping...