Insights into the subunit arrangement and diversity of paradoxin and taipoxin

• Purification of paradoxin and taipoxin from whole snake venom.
• Analysed the native state of these trimers using mass spectrometry.
• Demonstrate that these toxins have similar architectures.
• Reveal that paradoxin and taipoxin contain previously uncharacterised subunits.
• Taipoxin exists as two distinct populations, due to multiple γ isoforms.

Paradoxin and taipoxin are neurotoxic phospholipases from the inland and coastal species of Australian taipan. Despite their relatively high sequence homology of 70% and 84% for the acidic and basic chains respectively, they differ substantially in reported assays of neurotoxicity. This study provides the first characterisation of paradoxin, which like taipoxin, is a trimer at physiological pH. More broadly, these toxins were found to be composed of a more diverse range of subunits than previously recognised, including newly discovered γTPx isoforms, which give rise to an additional, major conformation of TPx.

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