Purification and Characterization of Punein, a Pomegranate PR-4 Protein Showing Structural Similarities with the Hevein Precursor

The detection of molecules belonging to the pathogenesis-related protein-4 (PR-4) family as a cause of allergic reactions towards the pomegranate fruit has already been suggested, although information regarding their isolation and characterization is not available in the literature. The objective of this study was the purification and description of some features of a pomegranate PR-4 protein. This protein, named punein, was purified by classical biochemical methods, identified by direct protein sequencing and mass spectrometry and analyzed by bioinformatic tools. Biochemical characterization shows that punein has a molecular mass of 13.29 kDa by mass spectrometry and about 14 kDa on SDS-PAGE, and it displays a blocked N-terminus. Bioinformatic analysis highlights that its primary structure shows similarity with the allergens prohevein (containing the strong allergen Hev b 6) and Bra r 2, from latex and turnip, respectively. In particular, punein could be aligned with the C-terminal region of prohevein, which shows IgE epitope regions, the amino acid sequences of which are partially conserved in the two molecules. However, further investigations are needed to understand the clinical relevance of this PR-4 food protein and the factors affecting the concentration of specific proteins, including punein, that are recognized by the immune systems of patients sensitized to pomegranate.