Identification of putative protein partners of a hyperstable cysteine-rich peptide derived from Acanthopanax trifoliatus

Abstract

Cysteine-rich peptides (CRPs) are an underexplored chemical constituent in plants. They have several features which are favorable for drug design and development. These features include their compact structure, relatively small size, and hyper-stability against proteolytic degradation. Acanthopanax trifoliatus is a traditional Chinese medicine commonly used to treat cancer, inflammation, and cardiovascular diseases. This study reports the identification and characterization of an 8-cysteine CRP, actritide aT1, from A. trifoliatus. Using mass spectrometry and transcriptomic analysis, actritide aT1 was shown to be a 35-residue long anionic peptide with four disulfide bonds. Stability assays showed that actritide aT1 is proteolytically stable against pepsin and trypsin. Fmoc-based Solid Phase Peptide Synthesis and oxidative folding were used to prepare the synthetic N-terminal biotinylated actritide aT1 for affinity enrichment mass spectrometry analysis. Our results showed that actritide aT1 interacts with the different subunits of Protein Phosphatase 2A (PP2A) including PPP2R1A, PPP2R2A, and PPP2R2D. To support this finding, we performed a Serine/ Threonine Phosphatase assay and demonstrated that actritide aT1 exerts PP2A inhibitory activities. In conclusion, this study identified and functionally characterized a novel 8-cysteine CRP from A. trifoliatus that is proteolytic stable and targets PP2A.