snake image courtesy of whozoo.org

The purpose of this site is to give a brief overview of some biochemical properties of dendrotoxin and a few elements from the biological and chemical research; it aims to stimulate interest and pass on a couple of the intriguing hints from the literature. Please see the sources for more topic expertise and feel free to email me with any questions.

Reptile   ||   Molecule   ||   Bibliography

Green Mamba's Dendrotoxin and Clues for Neural Biochemistry

Featured Creature1

The green mamba snake of sub-Saharan Africa (Dendroaspis angusticeps) lives primarily in trees and thickets, but is known to hunt rodents and birds on the ground as well. It is common in most of East Africa from Kenya to Zimbabwe and grows to 4-7 feet long. Green mambas are good climbers, very fast, and agile. For an exciting, first-hand encounter with this reptile, read "The Green Mamba" in Roald Dahl's book Going Solo.2 It is not a particularly agressive snake in comparison to its feared cousin, the black mamba, which dwells in more open spaces, such as a savanna, and has a reputation for being ready to attack or pursue prey. Both snakes produce a very strong venom (the lethal dose of green mamba venom for a human being is 15 milligrams). In a victim, symptoms of envenomation usually include systemic neurologic manifestations such as drowsiness, relatively little pain at bite location, swelling, and sometimes early paralysis, ventilatory/heart failure, or death (which may ensue rapidly).3 Anti-venom, "dendroaspis," is available in 10-ml. ampules from the Institut Pasteur Production, 3 Boulevard Raymond-Poincare, 92430 Marne la Coquette, France. This is prepared from purified horse serum, drawn from animals which have gradually been treated with the venom to produce immunity. A "Polyvalant" snake antivenom for several species, also effective for the green mamba, can be obtained from the South African Institute of Medical Research, P.O. Box 1038 Johannesburg 2000.

Source of molecular images: Protein Data Bank
(http://www.rcsb.org/pdb/), Berman, Westbrook, Feng, Gilliland,
Bhat, Weissig, Shindyalov, Bourne:
The Protein Data Bank. Nucleic Acids Research, accessed April 5-10, 2003

Image of a-DTX molecule from the Protein Data Bank

Action of Alpha-Dendrotoxin (a-DTx)

Green mambas secrete a pre-synaptic neurotoxin and proteinase inhibitor, which works by blocking potassium channels in the space between nerve synapses. Similar to the action of several other snake venoms, the a-DTX binds to voltage activated potassium channels and facilitates release of neural transmitters at peripheral and central synapses.4 Cholinergic agonists mainly excite or inhibit the autonomic effector cells (responsive to parasympathetic neurons) and are referred to as "parasympathomimetic" [mimicking the neuronal] agents5.

Research in molecular biology has identified and studied some of the chemical transmitters at the synapse of nerve cells by using pharmacological agents which react with the synaptically released transmitter in an identical way. The scientists seek natural substances with very specific electrochemical action, like the K+ -induced depolarization that causes the release of amino acid transmitters in the synaptic channel.6 Both carriers and electro-chemical channels have been proposed in connection with the transport of substrates across neurological membranes. Many experiments have tried to define or isolate transport substances and mechanisms.7 In another example, polyamine spider toxins are being used to study inhibitory mechanisms of micro-molar voltage, Ca+ activated currents in neurons.8

In 1991, Tadeusz Skarzynski of Blackett Laboratory, Imperial College, London, compared dendrotoxin to bovine pancreatic trypsin inhibitor [two molecules that are similar in their relation to potassium ion channels, though dendrotoxin is smaller.] He had noticed that a-DTX, a smaller molecule than the bovine one, was unable to inhibit trypsin, and his research pointed to different electrostatic interactions with the proteins on the enzyme side chains. Over the last decade or so, chemical researchers have found compound similarities between the protease inhibitors like several snake toxins and the amyloid beta-protein precursor found in Alzheimer's patients.9 Closer study of the (noticeably very specific) binding action of the venom toxins, may eventually offer better understanding of Alzheimer's and other human neurological disorders. Image of the bovine protease inhibitor courtesy of IMB Jena Image Library of Biological Macromolecules

In the effort to solve the structure of the a-DTX molecule, more than 30 partial or complete data sets of crystals soaked in different heavy-atom solutions were examined. Rotation function calculations employed a variety of models and search procedures, and an ideal model was worked out by Hendrickson-Konnert in 1985, using a "restrained least squares" program. The final refined model consisted of 477 protein atoms, five sulphate ions, and 59 water molecules. The molecular weight is 7138. All main-chain atoms could be mapped for electron density with Fourier coefficients, allowing clear interpretation.10

Bibliography and Sources

  1. Spawls, S., and Branch, B., The Dangerous Snakes of Africa, Ralph Curtis Publishing, London:1995, pp. 45, 156.
  2. Dahl, R., Going Solo, Puffin Books, New York:1986, p.41.
  3. Journal of Biological Chemistry, Nov. 5,1992, Vol. 267 (31:22122-30).
  4. Skarzynski, T., Journal of Molecular Biology, 1992, Vol. 224, pps. 670-683 "Crystal Structure of a-Dendrotoxin from the Green Mamba Venom and its Comparison with the Structure of Bovine Pancreatic Trypsin Inhibitor."
  5. King, Michael W., Indiana State University School of Medicine, "Biochemistry of Neural Transmitters," in General Principles of Biochemistry , http://web.indstate.edu/thcme/mwking/, (accessed 2/27/03).
  6. Bradford, H.F., Metabolism and Transmitter Function of Amino Acids in the Nervous System, Department of Biochemistry, Imperial College of Science and Technology, London:1975, pp. 268-273.
  7. Dobler, Max, Ionophores and Their Structures, Swiss Federal Institute of Technology, Wiley & Sons, New York:1981, p. 223.
  8. ibid., Skarzynski.
  9. ibid., Skarzynski.
  10. The Protein Data Bank, State University of New Jersey, Rutgers, San Diego Supercomputer Center at the University of California-San Diego, National Institute of Standards and Technology, and University of Wisconsin-Madison; from website, http://www.rcsb.org/pdb/, (accessed 2/26/03).
  11. Reichert, J.; Jabs, A.; Slickers, P.; Sühnel, J., IMB Jena Image Library of Biological Macromolecules, Institute of Molecular Biotechnology, Jena, Germany, from website, http://www.imb-jena.de/IMAGE.html (accessed 3/5-6/03).