Bullfrog protein found to be antidote for deadly shellfish poison
San Francisco: Hidden within the humble bullfrog’s genetics is the equipment to produce an antidote to a deadly shellfish toxin that afflicts thousands of people every year.
Scientists have found that a protein called saxiphilin, which occurs naturally in bullfrogs and other frogs around the world, can neutralize saxitoxin (STX) – the poison behind paralytic shellfish poisoning (PSP).
STX is produced by algal blooms known as “red tide” and accumulates in shellfish. It is considered a chemical weapon under international law, was stockpiled by the US during the Cold War, and featured in the famous case of American Air Force pilot Gary Powers, whose U-2 spy aircraft was shot down over the Soviet Union. The CIA had issued Powers a suicide pin containing STX.
Paralytic shellfish poisoning affects some 2,000 people worldwide officially, although experts say the vast majority of cases go unreported. There is currently no antidote for STX.
In research published July 16th in Nature Communications, a team led by Daniel Minor, PhD, and professor in UCSF’s Cardiovascular Research Institute, found that saxiphilin can neutralize saxitoxin in mice, preventing and even reversing otherwise lethal poisoning.
The protein acts like a molecular sponge. It binds tightly to saxitoxin in the bloodstream before the toxin can reach the nerve and muscle cells it normally attacks.”It turns out that one naturally occurring protein is all that’s required to take this toxin out of commission,” Minor said.
The discovery builds on 2021 research in which Minor and colleagues showed that saxiphilin binds strongly to saxitoxin. To test if it worked inside a living organism, Minor and postdoctoral scholars Samantha Nixon and Sandra Zakrzewska tested saxiphilin in mice exposed to lethal doses of STX. When given before or along with STX, the protein prevented poisoning. It also cured nearly all mice who got the protein after exposure, a scenario that most closely resembles what occurs when someone unknowingly eats poisoned shellfish.
“We had this really big protein that needed to catch up with a tiny toxin molecule that has a running start on it,” Minor said. “We really weren’t sure this was going to work.”The protein not only improved survival but also reduced symptoms associated with severe poisoning, with no harmful side effects. The team also discovered that saxiphilin spread throughout the body, reaching the brain, heart, and muscles.
STX is not a single toxin but a family of over 50 variants. In two studies published in 2025 and 2026, Minor showed that saxiphilin can bind a wide range of these variants.
The discovery could have important public health implications, helping to protect recreational harvesters worldwide, as well as coastal indigenous communities in the US and Canada who face the highest exposure to red tide through traditional subsistence harvesting, often far from emergency medical care.
His next goal is to determine whether smaller, engineered versions of saxiphilin could provide the same, or maybe even better, protection.
