Summary: Hemolytic toxin N terminal
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Hemolysin Edit Wikipedia article
||This article lends undue weight to certain ideas, incidents, or controversies. (January 2013)|
Hemolysins (UK spelling: haemolysins) are lipids and proteins that cause lysis of red blood cells by destroying their cell membrane. Although the lytic activity of some microbe - derived hemolysins on red blood cells may be of great importance for nutrient acquisition, many hemolysins produced by pathogens do not cause significant destruction of red blood cells during infection. Although hemolysins are capable of doing this for red blood cells in vitro.
- 1 Properties
- 2 Mechanism
- 3 Structure
- 4 Role during infection
- 5 Treatment
- 6 Applications
- 7 See also
- 8 References
- 9 External links
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:
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 are able 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 that 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 ion 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 that is freed by this kind of bacterium. These subunits are attached to the target cells, the way we have already explained, 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 that 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 that 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 hemolysin is related to bacteria not only in this way but also in some others.
As mentioned before, hemolysin is a potential virulence factor produced by microorganisms, which can put a 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 a 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 does not arrive to body tissues properly. As a consequence, 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 that thrives within host cells, mainly macrophages and monocytes) causes the degradation of phagosome 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 has been proven 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, which is the reason for the many studies in the field of immunology aimed at developing 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 has 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 that 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 the bloodstream dead 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 is 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.
- 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.
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- 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.
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- 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.
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- "What Is Hemolytic Anemia? - NHLBI, NIH". United States National Institutes of Health. 2011-04-01. Retrieved 2012-11-24.
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- 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. 338 (2): 124–31. 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): 1865–7. doi:10.4161/auto.22161. 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.
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- Hemolysins at the US National Library of Medicine Medical Subject Headings (MeSH)
- Hemolysin at eMedicine Dictionary
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Hemolytic toxin N terminal Provide feedback
This domain family is found in bacteria, and is approximately 190 amino acids in length. The family is found in association with PF07968 PF00652. This family is a bacterial virulence factor - hemolysin - which forms pores in erythrocytes and causes them to lyse.
Han JH, Lee JH, Choi YH, Park JH, Choi TJ, Kong IS;, Biochim Biophys Acta. 2002;1599:106-114.: Purification, characterization and molecular cloning of Vibrio fluvialis hemolysin. PUBMED:12479411 EPMC:12479411
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This tab holds annotation information from the InterPro database.
InterPro entry IPR022220
This domain family is found in bacteria, and is approximately 190 amino acids in length. The family is found in association with , . This family is a bacterial virulence factor - hemolysin - which forms pores in erythrocytes and causes them to lyse.
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|Number in seed:||7|
|Number in full:||120|
|Average length of the domain:||176.30 aa|
|Average identity of full alignment:||68 %|
|Average coverage of the sequence by the domain:||28.55 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||3|
|Download:||download the raw HMM for this family|
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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.
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 Hemolysin_N domain has been found. There are 15 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.
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