Paralytic shellfish poisoning (PSP) is triggered by saxitoxin (STX), a neurotoxin that can shut down nerve signaling and lead to rapid death. As “red tide” algal blooms become more frequent along the Pacific coast and beyond, exposure risks rise worldwide, yet effective medical countermeasures have remained limited. STX has also been historically stockpiled as a chemical weapon, underscoring the urgency of safe, scalable defenses.
Researchers at UC San Francisco report a strategy that treats the problem at its earliest step: neutralizing STX in the bloodstream before it can reach its neural and muscular targets. In a Nature Communications study published July 16, a bullfrog-derived protein called saxiphilin is shown to bind saxitoxin with high affinity, preventing the toxin’s toxic action.
Saxiphilin acts as a molecular “sponge.” Biophysically, its binding pocket recognizes STX’s distinctive shape, sequestering the toxin and reducing its bioavailability. Instead of attempting to disrupt STX’s downstream mechanisms or stimulate an immune response, the approach relies on direct physical interception.
The team tested saxiphilin in mice challenged with otherwise lethal STX doses. When administered before or alongside the toxin, saxiphilin prevented poisoning. Importantly, nearly all mice treated after exposure survived, closely mirroring real-world scenarios in which contaminated shellfish are eaten before symptoms prompt intervention.
Beyond survival, saxiphilin reduced clinical signs of severe poisoning and showed no harmful side effects in the study. Tracking experiments indicated the protein distributes throughout the body, including reaching the brain, heart, and muscles—allowing it to intercept toxin molecules across multiple tissues as STX circulates.
Earlier work established that saxiphilin binds STX strongly in vitro, but the new study addresses the missing translational step: whether a large binding protein can work in vivo against a small molecule that can rapidly exert toxicity. The results suggest that pharmacokinetic reach is sufficient to overcome the toxin’s initial “head start.”
The discovery also connects to a historical line of UCSF investigations from the late 1920s and 1930s. At the time, Hermann Sommer studied outbreaks of shellfish poisoning and noted that some frogs appeared resistant—an observation now explained by saxiphilin’s robust binding to saxitoxin.
Because STX exists as a family of more than 50 closely related variants, broad coverage matters. Prior UCSF work showed saxiphilin can bind diverse STX forms, supporting its potential as a general countermeasure rather than a variant-specific one.
Finally, the same binding principle could aid public health. If saxiphilin—or engineered derivatives—can serve as a sensitive detection molecule, shellfish screening could become faster and more reliable during bloom events, improving food safety in real time.
Subject of Research: Saxitoxin neutralization using the frog protein saxiphilin
Article Title: Saxiphilin neutralizes saxitoxin in vivo (study led by Daniel Minor)
News Publication Date: July 16
Web References: https://doi.org/10.1038/s41467-026-75136-z
References: 2021 UCSF study; related STX-binding papers (2025, 2026) mentioned in the news text
Image Credits: Sandra Zakrzewska, Minor Lab
Keywords: saxitoxin, paralytic shellfish poisoning, saxiphilin, molecular binding, neurotoxins, algal blooms, countermeasure, biosafety
