Acetylcholine Receptor and its Reaction to Cobra Venom

Structure

The acetylcholine receptor is composed of five alpha helical chains each with about 370 amino acids. This is a transmembrane protein forming a funnel into the cytosol of the cell.

Function as a Signal Molecule Receptor

The neurotransmitter acetylcholine is released into the synaptic cleft and is bound to the acetylcholine receptor. Consequently, the receptor changes conformation to release potassium ions into the cytoplasm of the cell while sodium ions are ejected from the cell through the receptor acting as an ion-gated channel. This change in ion concentration causes a change in the membrane potential of the cell. The release of sodium into extracellular matrix causes a release of more acetylcholine in a neighboring cell continuing the action potential across nerve cells. Nerve cell communication is also in control of muscle contraction. When the action potential traveling down the nerve cell reaches muscle tissue, the muscle cell responds by triggering a release in calcium to allow for muscle contraction for the organism to move.

Cobra Toxin

Cobra venom has several detrimental effects on their prey. This toxin blocks the acetylcholine receptor which causes paralysis of the muscles, including the diaphragm which leads to asphyxiation. Only about 1/3 of the acetylcholine receptors need to be blocked to cease function of the diaphragm resulting in death in as little as thirty minutes. The cobra toxin is 73 amino acid residues long in a single chain. The cobra toxin changes shape as it binds to the acetylcholine receptor. The blue indicates the amino acids that participate in binding to the receptor.

Cobra Toxin interaction with Acetylcholine Receptor

When cobra venom is introduced into the body is moves along the bloodstream to a diaphragm muscle. It works as a postsynaptic neurotoxin binding to the receptor as an extracellular ligand by interacting with OH group leaving the acetyl choline channel open which releases ions used in creating an action potential. Without the ions the diaphragm muscle can not be activated to contract and will not move so an individual can not take a breath. There must be five molecules of cobra toxin (red) to block the receptor (blue) as each molecule binds with an individual alpha chain on the acetylcholine receptor. This molecule was generated by overlaying the receptor and venom using Swiss PDB viewer magic fit. The RMS (root mean square difference) of this overlay if 12.21 angstroms involving 185 different atoms. The second image depicts an individual toxin binding with one chain on the receptor, both in the same color. This representation shows each molecule of the .

Anti-Venom

There are only two ways to save a life after being infected with cobra venom the first being an artificial respirator to contract and expand the lungs until the diaphragm is able to start an action potential and contract on its own. The other option to a quick administration of an anti-venom. Anti-venom acts to bind the venom both in the receptor and in the bloodstream and allows for it to be excreted out of the body.

See also:

• Receptor
• Transmembrane (cell surface) receptors
• Ionotropic receptors