Summary: Snake toxin
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Snake venom Edit Wikipedia article
Snake venom is highly modified saliva containing zootoxins used by snakes to immobilize and digest prey or to serve as a defence mechanism against a potential predator or other threat. The venom produced by the snake's venom gland apparatus is delivered by an injection system of modified fangs that enable the venom to penetrate into the target.
The glands that secrete the zootoxins are a modification of the parotid salivary gland found in other vertebrates and are usually situated on each side of the head, below and behind the eye and encapsulated in a muscular sheath. The glands have large alveoli in which the synthesized venom is stored before being conveyed by a duct to the base of channeled or tubular fangs through which it is ejected.
Venoms contain more than 20 different compounds, mostly proteins and polypeptides. A complex mixture of proteins, enzymes, and various other substances with toxic and lethal properties serves to immobilize the prey animal, enzymes play an important role in the digestion of prey, and various other substances are responsible for important but non-lethal biological effects. Some of the proteins in snake venom have very specific effects on various biological functions including blood coagulation, blood pressure regulation, transmission of the nervous or muscular impulse and have been developed for use as pharmacological or diagnostic tools or even useful drugs.
Proteins constitute 90-95% of venom's dry weight and they are responsible for almost all of its biological effects. Among hundreds, even thousands of proteins found in venom, there are toxins, neurotoxins in particular, as well as nontoxic proteins (which also have pharmacological properties), and many enzymes, especially hydrolytic ones. Enzymes (molecular weight 13-150 KDa) make-up 80-90% of viperid and 25-70% of elapid venoms: digestive hydrolases, L-amino acid oxidase, phospholipases, thrombin-like pro-coagulant, and kallikrein-like serine proteases and metalloproteinases (hemorrhagins), which damage vascular endothelium. Polypeptide toxins (molecular weight 5-10 KDa) include cytotoxins, cardiotoxins, and postsynaptic neurotoxins (such as Î±-bungarotoxin and Î±-Cobratoxin), which bind to acetylcholine receptors at neuromuscular junctions. Compounds with low molecular weight (up to 1.5 KDa) include metals, peptides, lipids, nucleosides, carbohydrates, amines, and oligopeptides, which inhibit angiotensin converting enzyme (ACE) and potentiate bradykinin (BPP). Inter- and intra-species variation in venom chemical composition is geographical and ontogenic. Phosphodiesterases interfere with the prey's cardiac system, mainly to lower the blood pressure. Phospholipase A2 causes hemolysis by lysing the phospholipid cell membranes of red blood cells. Amino acid oxidases and proteases are used for digestion. Amino acid oxidase also triggers some other enzymes and is responsible for the yellow colour of the venom of some species. Hyaluronidase increases tissue permeability to accelerate absorption of other enzymes into tissues. Some snake venoms carry fasciculins, like the mambas (Dendroaspis), which inhibit cholinesterase to make the prey lose muscle control.
|L-amino-acid oxidase||All species|
|Transferases||Alanine amino transferase|
|Hydrolases||Phospholipase A2||All species|
|Alkaline phosphatase||Bothrops atrox|
|Acid phosphatase||Deinagkistrodon acutus|
|Ribonuclease 1||All species|
|Adenosine triphosphatase||All species|
|Factor-X activator||Viperidae, Crotalinae|
|Lyases||Glucosamine ammonium lyase|
Snake toxins vary greatly in their functions. Two major classifications of toxins found in snake venoms include neurotoxins (mostly found in elapids) and hemotoxins (mostly found in viperids). However, there are exceptions - an African spitting cobra Naja nigricollis's venom consists mainly of hemotoxins, while the Mojave rattlesnake's venom is primarily neurotoxic. However, there are numerous other different types of toxins which both elapids or viperids may carry.
|Î±-neurotoxins||Î±-Bungarotoxin, Î±-toxin, erabutoxin, cobratoxin|
|Î²-neurotoxins||Notexin, ammodytoxin, Î²-Bungarotoxin, crotoxin, taipoxin|
|Dendrotoxins||Dendrotoxin, toxins I and K|
|Cardiotoxins||y-Toxin, cardiotoxin, cytotoxin|
|Sarafotoxins||Sarafotoxins a, b, and c|
|Hemorrhagins||Phospholipase A2, mucrotoxin A, hemorrhagic toxins a, b, c..., HT1, HT2|
|Structure of a typical chemical synapse|
The beginning of a new impulse:
A) An exchange of ions (charged atoms) across the nerve cell membrane sends a depolarising current towards the end of the nerve cell (cell terminus).
B) When the depolarising current arrives at the nerve cell terminus, the neurotransmitter acetylcholine (ACh), which is held in vesicles, is released into the space between the two nerves (synapse). It moves across the synapse to the postsynaptic receptors.
C) If ACh remains at the receptor, the nerve stays stimulated, causing incontrollable muscle contractions. This condition is called tetany. An enzyme called acetylcholinesterase destroys the ACh so tetany does not occur.
These toxins attack cholinergic neurons (those that use ACh as a transmitter) by destroying acetylcholinesterase (AChE). ACh therefore cannot be broken down and stays in the receptor. This causes tetany, which can lead to death. The toxins have been called fasciculins since after injection into mice, they cause severe, generalized and long-lasting (5-7 h) fasciculations.
Dendrotoxins inhibit neurotransmissions by blocking the exchange of positive and negative ions across the neuronal membrane lead to no nerve impulse, thereby paralysing the nerves.
Snake example: Mambas
This is a large group of toxins, with over 100 postsynaptic neurotoxins having been identified and sequenced. Î±-neurotoxins also attack cholinergic neurons. They mimic the shape of the acetylcholine molecule and therefore fit into the receptors â they block the ACh flow â feeling of numbness and paralysis.
- Sea snake (known as erabutoxin)
Phospholipase is an enzyme that transforms the phospholipid molecule into a lysophospholipid (soap) ==> the new molecule attracts and binds fat and ruptures cell membranes.
Snake example: Japanese Habu
Cardiotoxins are components that are specifically toxic to the heart. They bind to particular sites on the surface of muscle cells and cause depolarisation ==> the toxin prevents muscle contraction. These toxins may cause the heart to beat irregularly or stop beating, causing death.
The toxin causes hemolysis, or destruction of red blood cells (erythrocytes).
Snake cytotoxin IPR003572
Snake venom consists of many different toxin proteins: these can either have enzymatic activity, which typically assists in digestion, or can be shorter peptides that are used to immobilize prey. Toxin proteins make up many multigene families, and arose from gene recruitment of proteins that do not code for toxins, followed by extensive evolutionary modification. Toxin evolution follows the birth-and-death model of gene families, where duplication followed by functional diversification results in the creation of structurally related proteins that have slightly different functions. It is thought that venom as a way to immobilize prey was beneficial in allowing the uncoupling of feeding system and locomotion, which are coupled in the Haenophidians, which then enabled snakes with venom systems to colonize open areas. Venom continue to evolve as specific toxins are modified to target a specific prey, and it is found that toxins vary according to diet in some species.
The presence of enzymes in snake venom was once believed to be an adaptation to assist digestion. However, studies of the western diamondback rattlesnake, a snake with highly proteolytic venom, show that venom has no impact on the time required for food to pass through the gut.
In the vipers, which have the most highly developed venom delivery apparatus, the venom gland is very large and is surrounded by the masseter or temporal muscle, which consists of two bands, the superior arising from behind the eye, the inferior extending from the gland to the mandible. A duct carries venom from the gland to the fang. In vipers and elapids, this groove is completely closed, forming a hypodermic needle-like tube. In other species, the grooves are not covered, or only partially covered. From the anterior extremity of the gland, the duct passes below the eye and above the maxillary bone, to the basal orifice of the venom fang, which is ensheathed in a thick fold of mucous membrane. By means of the movable maxillary bone hinged to the prefrontal bone and connected with the tranverse bone which is pushed forward by muscles set in action by the opening of the mouth, the fang is erected and the venom discharged through the distal orifice. When the snake bites, the jaws close and the muscles surrounding the gland contract, causing venom to be ejected via the fangs.
 Mechanics of biting
Several genera, including Calliophis, Atractaspis and Causus, are remarkable for having exceptionally long venom glands, extending along each side of the body, in some cases extending posterially as far as the heart. Instead of the muscles of the temporal region serving to press out the venom into the duct, this action is performed by those of the side of the body.
There is considerable variability in biting behavior among snakes. When biting, viperid snakes often strike quickly, discharging venom as the fangs penetrate the skin, and then immediately release. Alternatively, as in the case of a feeding response, some viperids (e.g. Lachesis) will bite and hold. A proteroglyph or opisthoglyph, may close its jaws and bite or chew firmly for a considerable time.
 Mechanics of spitting
Spitting cobras of the genera Naja and Hemachatus, when irritated or threatened, may eject streams or a spray of venom a distance of 4 to 8 feet. These snakes' fangs have been modified for the purposes of spitting: inside the fangs, the channel makes a ninety degree bend to the lower front of the fang. Spitters may spit repeatedly and still be able to deliver a fatal bite.
Spitting is a defensive reaction only. The snakes tend to aim for the eyes of a perceived threat. A direct hit can cause temporary shock and blindness through severe inflammation of the cornea and conjunctiva. Although usually there are no serious results if the venom is washed away immediately with plenty of water, blindness can become permanent if left untreated. Brief contact with the skin is not immediately dangerous, but open wounds may be vectors for envenomation.
 Some effects
There are four distinct types of venom that act on the body differently.
- Proteolytic venom dismantles the molecular structure of the area surrounding and including the bite.
- Hemotoxic venoms act on the heart and cardiovascular system.
- Neurotoxic venom acts on the nervous system and brain.
- Cytotoxic venom has a localized action at the site of the bite.
It is noteworthy that the size of the venom fangs is in no relation to the virulence of the venom. The comparatively innocent Indo-Malay Lachesis alluded to above have enormous fangs, whilst the smallest fangs are found in the Hydrophids which possess very potent venom.
 Proteroglyphous snakes
The effect of the venom of proteroglyphous snakes(Hydrophids, Bungarus, Dendroaspis, Elaps, Pseudechis, Notechis, Acanthophis) is mainly on the nervous system, respiratory paralysis being quickly produced by bringing the venom into contact with the central nervous mechanism which controls respiration; the pain and local swelling which follow a bite are not usually severe.
The bite of all the proteroglyphous elapids, even of the smallest and gentlest, such as the Elaps or coral snakes, is, so far as known, deadly to humans.
Viper venom (Daboia, Echis, Lachesis, Crotalus) acts more on the vascular system, bringing about coagulation of the blood and clotting of the pulmonary arteries; its action on the nervous system is not great, no individual group of nerve-cells appears to be picked out, and the effect upon respiration is not so direct; the influence upon the circulation explains the great depression which is a symptom of viperine envenomation. The pain of the wound is severe, and is speedily followed by swelling and discoloration. The symptoms produced by the bite of the European vipers are thus described by Martin and Lamb:
The bite is immediately followed by local pain of a burning character; the limb soon swells and becomes discoloured, and within one to three hours great prostration, accompanied by vomiting, and often diarrhoea, sets in. Cold, clammy perspiration is usual. The pulse becomes extremely feeble, and slight dyspnoea and restlessness may be seen. In severe cases, which occur mostly in children, the pulse may become imperceptible and the extremities cold; the patient may pass into coma. In from twelve to twenty-four hours these severe constitutional symptoms usually pass off; but in the meantime the swelling and discoloration have spread enormously. The limb becomes phlegmonous, and occasionally suppurates. Within a few days recovery usually occurs somewhat suddenly, but death may result from the severe depression or from the secondary effects of suppuration. That cases of death, in adults as well as in children, are not infrequent in some parts of the Continent is mentioned in the last chapter of this Introduction.
The Viperidae differ much among themselves in the toxicity of their venom. Some, such as the Indian Daboia russelli and Echis carinatus; the American vipers Crotalus, Lachesis muta and Bothrops lanceolatus; and the African Causus, Bitis, and Cerastes, cause fatal results unless a remedy is speedily applied. On the other hand, the Indian and Malay Lachesis seldom cause the death of humans, their bite in some instances being no worse than the sting of a hornet. The bite of the larger European vipers may be very dangerous, and followed by fatal results, especially in children, at least in the hotter parts of the Continent; whilst the small Vipera ursinii, which hardly ever bites unless roughly handled, does not seem to be possessed of a very virulent venom, and, although very common in some parts of Austria-Hungary, is not known to have ever caused a serious accident.
 Opisthoglyphous colubrids
Biologists had long known that some snakes had rear fangs, 'inferior' venom injection mechanisms that might immobilize prey; although a few fatalities were on record, until 1957 the possibility that such snakes were deadly to humans seemed at most remote. The deaths of two prominent herpetologists from African colubrid bites changed that assessment, and recent events reveal that several other species of rear-fanged snakes have venoms that are potentially lethal to large vertebrates.
Boomslang and twig snake venom are toxic to blood cells and thin the blood (hemotoxic, hemorrhagic). Early symptoms include headaches, nausea, diarrhea, lethargy, mental disorientation, bruising and bleeding at the site and all body openings. Exsanguination is the main cause of death from such a bite.
The Groen Boomslang's venom is the most potent of all rear-fanged snakes in the world based on LD50. Although its venom may be more potent than some vipers and elapids, it causes fewer fatalities owing to various factors (for example, the fangs' effectiveness is not high compared with many other snakes: the venom dose delivered is low, and boomslangs are generally less aggressive in comparison to other venomous snakes such as cobras and mambas).
 Aglyphous snakes
Experiments made with the secretion of the parotid gland of Tropidonotus and Zamenis have shown that even aglyphous snakes are not entirely devoid of venom, and point to the conclusion that the physiological difference between so-called harmless and venomous snakes is only one of degree, just as there are various steps in the transformation of an ordinary parotid gland into a venom gland or of a solid tooth into a tubular or grooved fang.
 Among snakes
The question whether individual snakes are immune to their own venom has not yet been definitively settled, though there is a known example of a cobra which self-envenomated, resulting in a large abscess requiring surgical intervention but showing none of the other effects that would have proven rapidly lethal in prey species or humans. Furthermore, certain harmless species, such as the North American Lampropeltis getula and the Brazilian Rhacidelus brazili, are proof against the venom of the crotalines which frequent the same districts, and which they are able to overpower and feed upon. The Tropical Rat Snake, Spilotes variabilis, is the enemy of the Fer-de-lance in St. Lucia, and it is said[by whom?] that in their encounters the Tropical Rat Snake is invariably the victor. Repeated experiments have shown the European Common Snake, Tropidonotus natrix, not to be affected by the bite of Vipera berus and Vipera aspis, this being due to the presence, in the blood of the harmless snake, of toxic principles secreted by the parotid and labial glands, and analogous to those of the venom of these vipers. Several North American species of Rat snakes as well as King snakes have proven to be immune or highly resistant to the venom of rattlesnake species.
 Among other animals
The Hedgehog, the Mongoose, the Honey Badger, the Secretary Bird and a few other birds that feed on snakes are known to be immune to a dose of snake venom. Whether the pig may be considered so is still uncertain, although it is well known that, owing to its subcutaneous layer of fat, it is often bitten without ill effect. The garden dormouse (Eliomys quercinus) has recently been added to the list of animals refractory to viper venom. Some populations of California Ground Squirrel are at least partially immune to Rattlesnake venom as adults.
 Among humans
The acquisition of human immunity against snake venom is one of the oldest forms of vaccinology known to date (about AD 60, Psylli Tribe). Research into development of vaccines that will lead to immunity is ongoing. Bill Haast, owner and director of the Miami Serpentarium injected himself with snake venom during most of his adult life, in an effort to build up an immunity to a broad array of venomous snakes. It is a practice known as mithridatism. Haast lived to age 100, and survived a reported 172 snake bites. He donated his blood to be used in treating snake-bite victims when a suitable anti-venom was not available. More than twenty of those individuals recovered.
 Traditional Treatments
The World Health Organization estimates that 80% of the worldâs population depends on traditional medicine for their primary health care needs. Methods of traditional treament of snake bite, although of questionable efficacy and perhaps even harmful, are nonetheless relevant.
Plants used to treat snakebites in Trinidad and Tobago are made into tinctures with alcohol or olive oil and kept in rum flasks called 'snake bottles'. Snake bottles contain several different plants and/ or insects. The plants used include the vine called monkey ladder (Bauhinia cumanensis or Bauhinia excisa, Fabaceae) which is pounded and put on the bite. Alternatively a tincture is made with a piece of the vine and kept in a snake bottle. Other plants used include: mat root (Aristolochia rugosa), cat's claw (Pithecellobim unguis-cati), tobacco (Nicotiana tabacum), snake bush (Barleria lupulina), obie seed (Cola nitida), and wild gri gri root (Acrocomia aculeata). Some snake bottles also contain the caterpillars (Battus polydamas, Papilionidae) that eat tree leaves (Aristolochia trilobata). Emergency snake medicines are obtained by chewing a three-inch piece of the root of bois canÃ´t (Cecropia peltata) and administering this chewed-root solution to the bitten subject (usually a hunting dog). This is a common native plant of Latin America and the Caribbean which makes it appropriate as an emergency remedy. Another native plant used is mardi gras (Renealmia alpinia)(berries), which are crushed together with the juice of wild cane (Costus scaber) and given to the bitten. Quick fixes have included applying chewed tobacco from cigarettes, cigars or pipes. Making cuts around the puncture or sucking out the venom had been thought helpful, in the past, but this course of treatment is now strongly discouraged 
Especially noteworthy is progress regarding the defensive reaction by which the blood may be rendered proof against their effect, by processes similar to vaccinationâantipoisonous serotherapy.
The studies to which we allude have not only conduced to a method of treatment against snake-bites, but have thrown a new light on the great problem of immunity.
They have shown that the antitoxic sera do not act as chemical antidotes in destroying the venom, but as physiological antidotes; that, in addition to the venom glands, snakes possess other glands supplying their blood with substances antagonistic to the venom, such as also exist in various animals refractory to snake venom, the hedgehog and the mongoose for instance.
 Regional venom specificity
Unfortunately, the specificity of the different snake venoms is such that, even when the physiological action appears identical, serum injections or graduated direct inoculations confer immunity towards one species or a few allied species only.
Thus, a European in Australia who had become immune to the venom of the deadly Australian Tiger Snake, Notechis scutatus, manipulating these snakes with impunity, and was under the impression that his immunity extended also to other species, when bitten by a Denisonia superba, an allied elapine, died the following day.
In India, the serum prepared with the venom of Naja tripudians has been found to be without effect on the venom of the two species of kraits of the genus Bungarus, and the Old World vipers Daboia russelli and Echis carinatus, and the pit viper Trimeresurus popeiorum. Daboia russelli serum is without effect on colubrine venoms, or those of Echis and Trimeresurus.
Antivenom snakebite treatment must be matched as the type of envenomation that has occurred.
These are not effective against coral snake envenomation, which requires a specific antivenom to their neurotoxic venom.
This article is based on the 1913 book The Snakes of Europe, by G. A. Boulenger, which is now in the public domain in the United States (and possibly elsewhere). Because of its age, the text in this article should not necessarily be viewed as reflecting the current knowledge of snake venom.
 See also
- "Reptile Venom Research". Australian Reptile Park. Retrieved 21 December 2010.
- (Edited by) Bauchot, Roland (1994). Snakes: A Natural History. New York City, NY, USA: Sterling Publishing Co., Inc. pp. 194â209. ISBN 1-4027-3181-7.
- (edited by) Halliday; Adler, Tim; Kraig (2002). Firefly Encyclopedia of Reptiles and Amphibians. Toronto, Canada: Firefly Books Ltd. pp. 202â203. ISBN 1-55297-613-0.
- Bottrall, Joshua L.; Frank Madaras, Christopher D Biven, Michael G Venning, and Peter J Mirtschin (30). "Proteolytic activity of Elapid and Viperid Snake venoms and its implication to digestion". Journal of Venom Research 1 (3): 18â28. PMC 3086185. PMID 21544178. Retrieved 26 December 2011.
- Mattison, Chris (2007 (first published in 1995)). The New Encyclopedia of Snakes. New Jersey, USA (first published in the UK): Princeton University Press (Princeton and Oxford) first published in Blandford. p. 117. ISBN 0-691-13295-X.
- CONDREA E, DEVRIES A, MAGER J (February 1964). "HEMOLYSIS AND SPLITTING OF HUMAN ERYTHROCYTE PHOSPHOLIPIDS BY SNAKE VENOMS". Biochim. Biophys. Acta 84: 60â73. PMID 14124757.
- RodrÃguez-Ithurralde, D.; R. Silveira, L. Barbeito, F. Dajas (1983). "Fasciculin, a powerful anticholinesterase polypeptide from Dendroaspis angusticeps venom". Neurochemistry International 5 (3): 267â274. doi:10.1016/0197-0186(83)90028-1. Retrieved 26 December 2011.
- Hodgson WC, Wickramaratna JC. In vitro neuromuscular activity of snake venoms. 2002.
- "Cloning and purification of Î±-neurotoxins from king cobra (Ophiophagus hannah)". Cat.inist.fr. Retrieved 2012-10-16.
- R.M. Kini (2007). "Evolution of Three-Finger Toxins - a Versatile Mini Protein Scaffold". Acta Chimica Slovenica 58 (4): 693â701.
- P. Juarez, I. Comas, F. Gonzalez-Candelas, J. J. Calvete (2008). "Evolution of Snake Venom Disintegrins by Positive Darwinian Selection". Molecular Biology and Evolution 25 (11): 2391â2407.
- V. J. Lynch (2007). "Inventing an arsenal: adaptive evolution and neofunctionalization of snake venom phospholipase A(2) genes". Bmc Evolutionary Biology 7.
- B.G. Fry, W. Wuster, R. M. Kini, V. Brusic, A. Khan, D. Venkataraman, A. P. Rooney (2003). "Molecular evolution and phylogeny of elapid snake venom three-finger toxins". Journal of Molecular Evolution 57 (1): 110â129.
- A. H. Savitzky (1980). "The Role of Venom Delivery Strategies in Snake Evolution". Evolution 34 (6): 1194â1204.
- S. Pahari, D. Bickford, B. G. Fry, R. M. Kini (2007). "Expression pattern of three-finger toxin and phospholipase A(2) genes in the venom glands of two sea snakes, Lapemis curtus and Acalyptophis peronii: comparison of evolution of these toxins in land snakes, sea kraits and sea snakes". Bmc Evolutionary Biology 7.
- A. Barlow, C. E. Pook, R. A. Harrison, W. Wooster (2009). "Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution". Proceedings of the Royal Society B-Biological Sciences 276 (1666): 2443â2449.
- M.D. McCue (1 Aug 2007). "Prey envenomation does not improve digestive performance in western diamondback rattlesnakes (Crotalus atrox)". J. Exp. Zool. A 307a (online early): 568â77. doi:10.1002/jez.411. PMID 17671964.
- Martin, Charles James; Lamb, George (1907). "Snake-poison and Snake-bite". In Allbutt, T.C., Rolleston N.D. A System of Medicine. London: MacMillan. pp. 783â821.
- "Sterile tail abscess in Naja annulifera - self-envenomation case". Retrieved 2 April 2009.
- Florida Trend. December 19, 2011 http://www.floridatrend.com/article.asp?page=1&aID=56043&slug=farewell-to-these-famous-floridians
|url=missing title (help). Retrieved 2 April 2012.
- Carol Rosenberg (1999-08-30). "Bill Haast obituary: Snake-venom believer Haast dies at 100 - Los Angeles Times". Articles.latimes.com. Retrieved 2012-10-16.
- Matt Schudel. "Bill Haast dies at 100: Florida snake man provided venom for snakebite serum". The Washington Post. Retrieved 2012-10-16.
- "Microsoft Word - Document10" (PDF). Retrieved 2012-10-16.
- "Treating Snake Bites". Ces.ncsu.edu. Retrieved 2012-10-16.
- "CDC - Venomous Snakes - NIOSH Workplace Safety and Health Topic". Cdc.gov. 2012-02-24. Retrieved 2012-10-16.
- http://www.savagelabs.com/Products/CroFab/Home/crofab_frame.htm Link to PDF for full prescribing information, retrieved 11/12/12
|Wikimedia Commons has media related to: Snake venom toxins|
- UMich Orientation of Proteins in Membranes families/superfamily-55 - Calculated orientations of snake venome toxins in the lipid bilayer
- UMich Orientation of Proteins in Membranes families/superfamily-90 - Calculated orientations of snake venom phospholipases A2 and myotoxins in the lipid bilayer
- LD50's for most toxic venoms.
- Australian Venom Research Unit - a general source of information for venomous creatures in Australia
- biomedcentral.com - Medicinal and ethnoveterinary remedies of hunters in Trinidad
- reptilis.net - How venom works
- snakevenom.net - Drying and storage of snake venom
- Jonassen I, Collins JF, Higgins DG (August 1995). "Finding flexible patterns in unaligned protein sequences". Protein Sci. 4 (8): 1587â95. doi:10.1002/pro.5560040817. PMC 2143188. PMID 8520485.
- Shaw IC (2007). "Chapter 19: Snake Toxins". In Waring RH, Steventon GB, Mitchell SC. Molecules of Death (Second ed.). River Edge, N.J: Imperial College Press. pp. 329â344. ISBN 1-86094-815-4.
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.
Snake toxin Provide feedback
A family of venomous neurotoxins and cytotoxins. Structure is small, disulfide-rich, nearly all beta sheet.
Internal database links
|Similarity to PfamA using HHSearch:||UPAR_LY6|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR003571
Snake toxins belong to a family of proteins [PUBMED:6433031] which groups short and long neurotoxins, cytotoxins and short toxins, as well as a other miscellaneous venom peptides. Most of these toxins act by binding to the nicotinic acetylcholine receptors in the postsynaptic membrane of skeletal muscles and prevent the binding of acetylcholine, thereby blocking the excitation of muscles.
Snake toxins are proteins that consist of sixty to seventy five amino acids. Among the invariant residues are eight cysteines all involved in disulphide bonds. The structure is small, disulphide-rich, nearly all beta sheet.
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)|
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We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the NCBI sequence database, and our metagenomics sequence database. More...
There are various ways to view or download the sequence alignments that we store. We provide several sequence viewers and a plain-text Stockholm-format file for download.
We make a range of alignments for each Pfam-A family:
- the curated alignment from which the HMM for the family is built
- the alignment generated by searching the sequence database using the HMM
- Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
- a Java applet developed at the University of Dundee. You will need Java installed before running jalview
- an HTML page showing the whole alignment.Please note: full Pfam alignments can be very large. These HTML views are extremely large and often cause problems for browsers. Please use either jalview or the Pfam viewer if you have trouble viewing the HTML version
- an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
- Pfam viewer
- an HTML-based viewer that uses DAS to retrieve alignment fragments on request
You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.
You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.
We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.
HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...
If you find these logos useful in your own work, please consider citing the following article:
This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.
Note: You can also download the data file for the tree.
Curation and family details
This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.
|Previous IDs:||toxin; toxin_1;|
|Number in seed:||48|
|Number in full:||594|
|Average length of the domain:||60.80 aa|
|Average identity of full alignment:||38 %|
|Average coverage of the sequence by the domain:||79.57 %|
|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:||16|
|Download:||download the raw HMM for this family|
Weight segments by...
Change the size of the sunburst
selected sequences to HMM
a FASTA-format file
- 0 sequences
- 0 species
This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.
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 Toxin_1 domain has been found. There are 141 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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