The Ingenious Method of Poison Dart Frogs to Secure Toxins in Their Skin

Poison dart frogs' skin toxins may be transported there by molecular shuttles, a recent study has suggested.

Poison dart frogs, part of the Dendrobatidae family, are known for carrying over 500 toxic alkaloid compounds, which they accumulate through consuming insects. However, the process by which these toxins travel from the frog's intestines to its skin has not been fully understood.

Researchers have now identified a protein, named Alkaloid Binding Globulin (ABG), that appears to act as a carrier for the toxins. This protein, which has similar traits to proteins that assist in hormone transport in mammals, collects these alkaloids from the frog's blood or intestines and transports them to the skin; a form of chemical defense. This new discovery was reported in eLife on December 19. This finding might assist researchers in creating similar proteins for use in humans, perhaps for absorbing toxins during cases of overdose.

Roberto Márquez, an evolutionary geneticist and herpetologist at the University of Michigan in Ann Arbor, says that this is the first time a poison-transporting protein connected to dart frogs has been uncovered.

Márquez notes that there has been a theory suggesting a significant metabolic aspect to the existence of "poison frogs as a ball of toxins." Proteins that could bind to alkaloids were suspected as being significant in allowing the toxins to move from food to skin while not being lethal to the frog itself.

One alkaloid-binding protein was found in a study conducted by biologist Aurora Alvarez-Buylla of Stanford University and her team by comparing a substance similar to a poison frog alkaloid known as pumiliotoxin with the blood serum from Diablito poison dart frogs (Oophaga sylvatica). The most common protein found to be attaching to the bait was ABG. The team also identified analogous proteins in two other frog species.

The protein they identified seemed to possess a natural attraction for pumiliotoxin and was able to absorb most of the available alkaloid. Analysis of Diablito frogs from Ecuador implied that the ABG protein originates in the liver of the frogs. Further tests involving fluorescent markers showed that the protein moved from the liver into the intestines and skin.

However, Alvarez-Buylla notes this newly recognized protein is "biochemically promiscuous," attaching to other frog toxins like epibatidine and decahydroquinoline in the laboratory. She suggested that there may still be countless other toxins for the team to experiment with.

Márquez also agrees that there are still unresolved questions regarding how many other toxins ABG might attach to and its prevalence across the entire poison dart frog species. He also highlighted it is not yet clear how the protein operates in transporting these toxic compounds. He adds, it’s a fascinating subject and with some aspects already clear, he's looking forward to gaining further understanding of how poison dart frogs handle their vast range of toxins.