Fasciculin

Investigations have revealed distinct forms in some green mamba venoms, in particular FAS1 and FAS2[1] Fasciculins are so called because they cause intense fasciculation in muscle fascicles of susceptible organisms, such as the preferred prey of the snakes.

The mechanism of action of FAS proteins is associated with attachment to molecules within muscular acetylcholinesterase, and at neuromuscular junctions, thus conferring their ability to interfere with neuromodulatory inhibition.

[2] Fasciculins from mambas inhibit mammalian and fish acetylcholinesterases intensely, but are less active against the corresponding enzymes in insects, reptiles and birds.

[2] That mechanism is in some ways similar to the effect of the so-called organophosphate nerve agents; the blockage of the acetylcholinesterase action is what causes the fasciculation that inspired the name fasciculin.

However, there is a significant, though reduced, toxic effect, because several basic residues in the venom protein still establish and maintain contacts with the enzyme.