Why are some recluse spider bites
much worse than others?

Substrate specificity of toxins offers clues

CENTERS FOR DISEASE CONTROL AND PREVENTION'S PUBLIC HEALTH IMAGE LIBRARY

Brown recluse spiders are common in the southern United States and have potent venoms. Bites from this family of spiders can cause necrotic ulcers and, in rare cases, the destruction of red blood cells, kidney failure and death.

In a recent Journal of Biological Chemistry paper, Matthew Cordes, a biochemistry professor at the University of Arizona, and co-workers uncovered why recluse spider venoms are so complex.

“The venom is really like a complicated cocktail – like a martini with five different brands of gin and vermouth in it,” Cordes explained. “Not only is it a particular kind of ingredient in the venom cocktail that makes brown recluse bites harmful to people, it seems that certain ‘brands’ of that ingredient are more likely than others to be poisoning people.”

Brown recluse spider venom contains many toxins, including a variety of phospholipase D enzymes, which attack the phospholipid cell membrane. Daniel Lajoie, a graduate student and the first author on the JBC paper, and co-workers discovered why recluse spider venoms have so many different phospholipase D enzymes: Some of the toxins have evolved to attack sphingomyelin, which is common in mammals and some insects, while other toxins have evolved to attack ethanolamine-containing sphingolipid, which is not found in humans but is common in insects the spiders prey on.

Figuring out the substrate specificity for the different toxins is only one step in the path to understanding why some recluse spider bites are much worse than others. Where the spider bite is located, the age of the person bitten, how much venom is injected and the composition of the venom are all important factors that affect how severe the bite is. Interestingly, Greta Binford, a biology professor at Lewis & Clark College, discovered that in addition to the species of the spider, the spider’s age and sex affect the precise composition of venom.

There is still work to be done to understand and treat brown recluse spider bites. For instance, it’s still a mystery how cleaving the headgroup off of the fatty acid portion of the phospholipid and forming a cyclic ceramide phosphate triggers a cascade of events leading to cell death.

However, stopping the toxins from attacking the cell membrane or preventing the downstream cascade triggered by their products are possible methods for treating recluse spider bites. This new research undertaken by the Cordes lab sheds light on the complexity and redundancy of the venom, informing future work toward treating brown recluse bites.

One interesting spinoff from this research is a new idea for an insecticide. One of the toxins found in the six-eyed sand spider is very effective at attacking ethanolamine-containing sphingolipid, a phospholipid common in insects but not found in humans.

Mollie Rappe Mollie Rappe earned her Ph.D. in biophysics at the Johns Hopkins University. She will begin writing for Sandia National Laboratories shortly.