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Cantharidin-binding protein: identification as protein phosphatase 2A
1Department of Entomological Sciences, University of California, Berkeley 94720.
Summary
Cantharidin and its analogs, like herbicide endothall, are toxic due to binding a protein. This protein, cantharidin-binding protein (CBP), is identified as protein phosphatase 2A (PP2A), explaining toxicity mechanisms.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Background:
- Cantharidin and analogs, including herbicide endothall, exhibit toxicity attributed to a specific binding protein.
- Understanding this interaction is crucial for elucidating toxic mechanisms and potential therapeutic interventions.
Purpose of the Study:
- To isolate and characterize the cantharidin-binding protein (CBP).
- To identify the molecular identity of CBP and its role in mediating toxicity.
- To investigate the biochemical properties of CBP and its interaction with cantharidin and its analogs.
Main Methods:
- Purification of CBP from mouse liver cytosol using multiple chromatographic steps.
- Characterization of CBP's subunit composition and amino acid sequences.
- Biochemical assays to assess CBP's enzymatic activity and inhibition by cantharidin, its analogs, and okadaic acid.
Main Results:
- CBP was purified to >99% purity, revealing a heterodimer of 61-kDa alpha and 39-kDa beta subunits.
- Amino acid sequencing identified CBP as protein phosphatase 2A (PP2A), specifically the PP2A-AC form.
- CBP/PP2A dephosphorylation activity was sensitive to cantharidin, its analogs, and okadaic acid, confirming the binding site interaction.
Conclusions:
- Cantharidin-binding protein (CBP) is identified as protein phosphatase 2A (PP2A).
- The toxicity of cantharidin and its analogs, such as endothall, likely results from the inhibition of PP2A activity.
- This finding provides a molecular basis for the diverse toxic effects of these compounds in mammals and potentially plants.