Tetanus toxin C-fragment, molecular model. This is a fragment of the neurotoxin protein produced by the bacterium Clostridium tetani that causes tetanus. This fragment is responsible for binding to lipids on the membranes of nerve cells (gangliosides). Once bound, other fragments of the protein use enzymatic properties to enter the cell. The toxin prevents the release of inhibitory neurotransmitters from the nerve cells, leading to muscle overactivity, or spasms. In this model the coils and arrows (solid colours) represent the protein's secondary structure, and the tubular structure behind (faded colours) shows individual atoms and bonds.