Tetanus toxin

Structure of tetanospasmin

Tetanus toxin, also known as tetanospasmin, is a potent neurotoxin produced by the bacterium Clostridium tetani. This toxin is responsible for the clinical condition known as tetanus, which is characterized by muscle spasms and rigidity. Tetanus toxin is one of the most potent toxins known, with an estimated lethal dose of less than 2.5 nanograms per kilogram of body weight.

Structure

Diagram of structure of tetanospasmin

Tetanus toxin is a protein composed of a single polypeptide chain that is cleaved into two subunits, a heavy chain and a light chain, linked by a disulfide bond. The heavy chain is responsible for binding to neuronal membranes, while the light chain acts as a zinc-dependent endopeptidase that cleaves synaptobrevin, a protein essential for neurotransmitter release.

Mechanism of Action

Mechanism of action of tetanospasmin

The mechanism of action of tetanus toxin involves several steps:

1. Binding: The heavy chain of the toxin binds to specific receptors on the surface of motor neurons.
2. Internalization: The toxin is internalized into the neuron via endocytosis.
3. Translocation: The light chain is translocated into the cytoplasm of the neuron.
4. Cleavage of Synaptobrevin: The light chain cleaves synaptobrevin, a component of the SNARE complex, which is crucial for the release of neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine.

This disruption in neurotransmitter release leads to the characteristic muscle spasms and rigidity seen in tetanus, as inhibitory signals are blocked, resulting in unopposed muscle contraction.

Clinical Significance

Tetanus toxin is the causative agent of tetanus, a serious disease that can be fatal if not treated promptly. The toxin's ability to block inhibitory neurotransmitter release leads to the hallmark symptoms of tetanus, including trismus (lockjaw), opisthotonos (severe hyperextension and spasticity), and autonomic instability.

Prevention and Treatment

The primary method of prevention is through vaccination with the tetanus toxoid, which is an inactivated form of the toxin that stimulates the immune system to produce protective antibodies. In cases of suspected tetanus exposure, tetanus immune globulin may be administered to neutralize the toxin. Treatment of tetanus involves supportive care, administration of muscle relaxants, and management of complications.

Related Pages

• Clostridium tetani
• Tetanus
• Neurotoxin
• Vaccination