The Black Mamba ( Dendroaspis polylepis ), also called the common black mamba or black-mouthed mamba, is the longest venomous snake in Africa. Its name stems from the colour of the inside of its mouth. The Black Mamba is commonly called "seven steps" snake because the extreme speed of the effect of its poison, absolutely lethal, would not permit a man, after the bite, to run for more than seven step. Since its venom is made of a protein of low molecular weight, the venom and its constituents are able to spread extraordinarily fast within the bitten tissue. This makes the black mamba venom the most rapid-acting of all snake venoms. Without proper care, the case fatality rate of its bite is 100%. This deadly poison is neurotoxic, which attacks the nervous system, causing paralysis of the vital organs, and death occurs in about 20 minutes from the byte and in some cases after few minutes. If bitten severe neurotoxicity often occurs: common symptoms are rapid onset of dizziness, drowsiness, coughing or difficulty in breathing, convulsions, and an erratic heartbeat. Other common effects are neuromuscular symptoms, shock, loss of consciousness, hypotension, pallor, ataxia, excessive salivation (oral secretions may become profuse and thick), limb paralysis, nausea and vomiting, fever, and very severe abdominal pain. Black Mamba
The venom contains three principal substances:
The first two have negative effects, while the last one has interesting applications in pain relief that have been recently discovered.
Dendrotoxin: Dendrotoxins are ~7kDa proteins consisting of a single peptide chain of approximately 57-60 aminoacids. Several homologues of alpha-dendrotoxin have been isolated, all possessing a slightly different sequence.
Dendrotoxins possess a very short 310-helix near the N-terminus of the peptide, while a two turn alpha-helix occurs near the C-terminus. A two-stranded antiparallel β-sheet occupies the central part of the molecular structure. These two β-strands are connected by a distorted β-turn region that is thought to be important for the binding activity of the protein. All dendrotoxins are cross-linked by three disulfide bridges, which add stability to the protein and greatly contribute to its structural conformation.
A single dendrotoxin molecule associates reversibly with a potassium channel in order to exert its inhibitory effect. It is proposed that this interaction is mediated by electrostatic interactions between the positively charged amino acid residues in the cationic domain of dendrotoxin and the negatively charged residues in the ion channel pore. Potassium channels, similar to other cation-selective channels, are believed to have a cloud of negative charges that precede the opening to the channel pore that help conduct potassium ions through the permeation pathway. It is generally believed (though not proven) that a dendrotoxin molecules bind to anionic sites near the extracellular surface of the channel and physically occlude the pore, thereby preventing ion conductance, even if some studies suggest that this substance inhibits this channel by altering his structure. (Energetic and structural interactions between delta-dendrotoxin and a voltage-gated potassium channel, 2000) .
Dendrotoxins have been shown to block particular subtypes of voltage-gated potassium channels (Kv1.1 and Kv1.2 channels) Dendrotoxins: Structure-Activity Relationships and Effects on Potassium Ion Channels. 2012 in neuronal tissue. In the nervous system, voltage-gated K+ channels control the excitability of nerves and muscles by controlling the resting membrane potential and by repolarizing the membrane during action potentials. This substance has been shown to bind the nodes of Ranvier of motor neurons and to block the activity of these potassium channels. In this way, dendrotoxins prolong the duration of action potentials and increase acetylcholine release at the neuromuscular junction, which may result in muscle hyperexcitability and convulsive symptoms. The progressive hyperexcitability of respiratory muscles may induce tetanic contraction of them leading to respiratory paralysis and death.
Calciseptine: this toxin consists of 60 amino acids with four disulfide bonds. Calciseptine specifically blocks L-Type calcium channels, but not other voltage-dependent calcium channels such as N-type and T-type: this block implies the lower contraction of heart tissue, leading to cardiovascular problems after the bite. This toxin has an action that resembles that of drug such as 1,4-dihydropyridines, which are important in the treatment of cardiovascular diseases.
Calciseptine, a peptide isolated from black mamba venom, is a specific blocker of the L-type calcium channel.
Application of Black Mamba venom in pain relief
Mambalgins Mambalgins classified as being part of the family of three-finger toxins. There are two isoforms of mambalgin which have been given the names of mambalgin-1 and mambalgin-2. Both of these isopeptides are made of a 57 aminoacidic chain with 8 residues of cysteine. These two isoforms differ only in the residue located in the fourth position of the chain.
Mambalgin-1 presents a three-dimensional structure which consists of 3 loops emerging from the nucleus of this protein. A triple chain with antiparallel β-sheets connects loops II and III, and a double chain, also formed by antiparallel β-sheets, allows the formation and bonding of loop I. Moreover, the protein presents a concave area, which is typical of neurotoxins, stabilized by four disulphide bonds.
Mambalgins also show a high electrostatic potential which is necessary for the bounding with the ASIC ionic channels, http://flipper.diff.org/app/items/5368 which are negatively charged.
These toxins have been proved to have a strong analgesic effect in both central and peripheral nerves, being able to be as potent as morphine but better because they cause less tolerance and no respiratory distress. http://www.ncbi.nlm.nih.gov/pubmed/?term=mambalgine
While morphine acts on the opioid pathway of the brain causing addiction, headaches, difficulty thinking and vomiting, mambalgins avoid pain using a completely different route, which is potentially capable of causing fewer side effects. Mambalgins have been found to take away pain by inhibiting acid-sensing ion channels (ASIC) in the peripheral and central nervous system.
When an external pain stimulus is received by the body, our damaged cells release an inflammatory soup containing ions and other chemicals. The ions released by the damaged cells are detected by the ASIC channels, which open up due to a change in the pH levels that the ions cause. As the protein ion channels open, they trigger the electric impulse sent to the brain telling him that the body is suffering.
What mambalgins do in order to avoid pain is that they bind to these ASIC channels and prevent them from opening, thus causing the body not to send pain messages to the brain and acting as a powerful analgesic.
Finally it is important to remember that mambalgins do not block all ion channels, because these kinds of toxins are normally highly specific. Researchers have found that mambalgins have a potent, rapid and reversible effect in homomeric ASIC1 and heteromeric ASIC1a+ASIC2a or ASIC1a+ASIC2b channels, which are the entire ASIC channel subtypes found in the central nervous system. On the other hand, they have no effect on ASIC2a, ASIC3, ASIC1a+ASIC3 and ASIC1b+ASIC3 channels.
Bringing mambalgins to a practical use, these peptides could be useful in the analgesic treatments of patients with chronic respiratory diseases, given that their effect seems not to affect the respiratory system, in contrast to morphine which can cause respiratory distress. In addition, this new potential drug seems to deal with the problem of tolerance using morphine, in other words, needing an increasingly higher dose each time to obtain the same effect. This would be of great use for the chronically ill, as they could take the analgesic as many times as they wanted without becoming addicts or dependant on the drug.