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Published on: March 29, 2022
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, San Francisco, CA 94158, USA.
Structure (London, England : 1993)
|June 17, 2026
Summary
Saxitoxin (STX) and its analogs are potent toxins that disrupt sodium channels. Frog saxiphilins show remarkable adaptability in binding these toxins, revealing new insights into toxin-protein interactions.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Saxitoxin (STX) and paralytic shellfish toxins (PSTs) are potent neurotoxins produced by harmful algal blooms.
- PSTs exert toxicity by blocking voltage-gated sodium channels (NaV), crucial for bioelectrical signaling.
- Understanding PST structural variations and their binding interactions is vital for developing countermeasures and therapeutic leads.
Purpose of the Study:
- To investigate the binding capabilities of frog and toad saxiphilins (Sxphs) with a diverse range of STX congeners.
- To elucidate the structural basis of STX congener binding to saxiphilins using high-resolution techniques.
- To explore the implications of these interactions for toxin countermeasure development and NaV modulator design.
Main Methods:
- Structural biology: High-resolution X-ray crystallography of saxiphilin-toxin complexes.
- Biochemical assays to assess binding affinity and specificity of various STX congeners to saxiphilins.
- Comparative analysis of binding modes across different STX analogs and saxiphilin variants.
Main Results:
- American bullfrog (RcSxph) and High Himalaya frog (NpSxph) saxiphilins bind a wide spectrum of C13-modified STX congeners.
- High-resolution structures reveal distinct "compact" and "open" binding modes for C13-aryl congeners, influenced by the RcSxph Tyr558 residue.
- Demonstrated significant adaptability of saxiphilins to diverse STX analogs and revealed unexpected conformational plasticity in the toxins themselves.
Conclusions:
- Frog saxiphilins exhibit remarkable structural adaptability in binding various saxitoxin analogs.
- The identified binding modes provide crucial insights into toxin-protein interactions and toxin conformational flexibility.
- These findings inform the design of novel sodium channel probes and modulators for therapeutic and research applications.
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