Biochemistry of spider venom
- Spider venoms can be split into two main groups: necrotic and neurotoxic
- Necrotic, or cytotoxic, venoms cause cell and tissue damage, leading to inflammation,
lesions and blisters
- Neurotoxic venoms attack the nervous system, interfering with neuron signaling, and can
lead to respiratory and cardiac arrest in extreme cases
- It should be noted that some spider venoms are not either necrotic or neurotoxic, but in fact
may contain both neurotoxic and necrotic components
- Venom components are often grouped based on molecular weight into low molecular
weight compounds (<1000), peptides (1000 – 10,000) and proteins (10,000 +)
- Low molecular weight compounds usually consist of salts, carbohydrates, and small
organic compounds such as amines, acids and acylpolyamines
- It’s thought that potassium ions in salts may assist toxic components of the venom to reach
their molecular targets. High concentrations of K+ can also affect signaling between
neurons in insects
- Amines can include neurotransmitters such as serotonin and noradrenaline, which similarly
can interfere with the nervous system, and also aid in spreading the venom through the
body
- Acylpolyamines are significant low molecular weight toxins which paralyse insects by
blocking glutamate receptors. Spider venoms may contain many types of acylpolyamines
- Peptides, however, are the main component in most spider venoms, making up about 25%
of spider venom on average, based on molecular weight. Indeed, it is thought that some
venoms can contain up to 1000 different peptides
- Some contain linear, cytolytic peptides which have necrotic effects. The action is relatively
non-specific, and they can also act synergistically with neurotoxic components
- The most important peptides, however, are those with disulfide bridges. These are the most
toxic component in many spider venoms
- Disulfide-containing peptides are more potent than cytolytic peptides, and are more
selective, usually acting on the ion channels of neurons
- Higher molecular weight components include enzymes and other larger proteins. Enzymes,
clearly, play a role in the external digestion, breaking down tissues and organs to be
consumed by the spider. Enzymatic extracellular structure breakdown also aids in enabling
the spread of the venom
- The enzyme hyaluronidase, however, is thought to be a self-defense component, as it
targets hyaluronan, a polysaccharide found in vertebrates, but not invertebrates
- High molecular weight proteins are fairly uncommon as toxic components in spider venom,
however an exception to this is the venom of the black widow spiders (Latrodectus spp.).
Their venoms contain toxins called Latrotoxins, one of which, α-latrotoxin, binds to nerve
terminals, causing huge release of neurotransmitters into synapses, blocking signal
transmission
