Saxitoxin (STX) is a potent neurotoxinand the best-known paralytic shellfish toxin (PST). Ingestion of saxitoxin, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the human illness known as paralytic shellfish poisoning (PSP).
The term saxitoxin originates from the genus name of the butter clam (Saxidomus) from which it was first isolated. But the term saxitoxin can also refer to the entire suite of more than 50 structurally related neurotoxins (known collectively as "saxitoxins") produced by algae and cyanobacteria which includes saxitoxin itself (STX), neosaxitoxin (NSTX), gonyautoxins(GTX) and decarbamoylsaxitoxin(dcSTX).
saxitoxin mechanism
Saxitoxin is a neurotoxin that acts as a selective sodium channel blocker.[15]One of the most potent known natural toxins, it acts on the voltage-gated sodium channels of neurons, preventing normal cellular function and leading to paralysis.
The voltage-gated sodium channel is essential for normal neuronal functioning. It exists as integral membrane proteins interspersed along the axon of a neuron and possessing four domains that span the cell membrane. Opening of the voltage-gated sodium channel occurs when there is a change in voltage or some ligand binds in the right way. It is of foremost importance for these sodium channels to function properly, as they are essential for the propagation of an action potential. Without this ability, the nerve cell becomes unable to transmit signals and the region of the body that it innervates is cut off from the nervous system. This may lead to paralysis of the affected region, as in the case of saxitoxin.
Saxitoxin binds reversibly to the sodium channel. It binds directly in the pore of the channel protein, occluding the opening, and preventing the flow of sodium ions through the membrane. This leads to the nervous shutdown explained above.