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Saxiphilin is a broad-spectrum toxin sponge for C13-modified saxitoxins
Sandra Zakrzewska1, Zhou Chen1, Elizabeth R Park2
1Cardiovascular Research Institute, University of California, San Francisco, CA 94158 USA.
Biorxiv : the Preprint Server for Biology
|April 10, 2026
Summary
Saxitoxin (STX) and its analogs bind frog saxiphilins, revealing adaptable toxin binding modes. This research informs the development of STX-based probes and sodium channel modulators.
Area of Science:
- Biochemistry
- Structural Biology
- Pharmacology
Background:
- Saxitoxin (STX) and paralytic shellfish toxins (PSTs) are potent neurotoxins produced by harmful algal blooms.
- These toxins disrupt voltage-gated sodium channels (NaV), interfering with bioelectrical signaling.
Purpose of the Study:
- To understand how structural variations in PSTs affect their binding to target proteins.
- To explore the potential of frog saxiphilins (Sxphs) as a platform for studying PST-protein interactions and developing countermeasures.
Main Methods:
- High-resolution X-ray crystallography was used to determine the structures of STX-Sxph complexes.
- The binding of American bullfrog (Rana catesbeiana) RcSxph and High Himalaya frog (Nanorana parkeri) NpSxph to various C13-modified STX congeners was investigated.
Main Results:
- Both RcSxph and NpSxph demonstrated broad binding capabilities for a range of C13-modified STX congeners.
- Two distinct binding modes, 'compact' and 'open', were observed for C13-aryl congeners, influenced by the RcSxph Tyr558 residue.
- The study revealed significant adaptability in Sxphs for accommodating diverse STX analogs and highlighted unexpected conformational plasticity of the toxins.
Conclusions:
- Saxiphilins exhibit remarkable versatility in binding chemically diverse saxitoxin analogs.
- These findings provide insights into PST interactions with biological targets and guide the design of novel STX-based probes and NaV modulators.
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