Tetanus toxin C-fragment (TTc) is a non-toxic 52kD polypeptide generated by papain cleavage of tetanus toxin, corresponding to the C-terminal 451aa. The illness known as Tetanus is caused by a neurotoxin produced by the anaerobic bacterium Clostridium tetani. C. tetani is commonly found in soil, feces, and on many objects lying on the ground, such as rusty metal, hence puncture wounds are a common cause of tetanus. It acts upon the presynaptic membranes of both central and peripheral nervous systems to block the release of neurotransmitters. In its toxic form tetanus neurotoxin is a 150kD protein, consisting of two major components: a light chain and heavy chain. The light chain contains the enzymatic portion of the toxin and is responsible for its toxic effects. The heavy chain binds to the neuron and aids delivery of the light chain to the neuron interior. A single disulfide bond links light and heavy chains.