Unveiled the nature of the ligand of Pru p 3, the major allergen from peach

Pru p 3 is the major allergen from peach, fruit which is among the most frequent causes of food allergy in the Mediterranean population. Although this lipid transfer protein has been well studied, its physiological function remains to be determined. Evidence gathered over the years points to a key role played by the ligand of Pru p 3 in the participation of this protein in processes in plant as well as in allergy sensitization processes in humans. However, the nature of the ligand, essential to elucidate that role, had remained hidden until now.

Our work has led to identify the ligand of Pru p 3 as a hydroxylated derivative of the alkaloid camptothecin bound to sphingosine. While sphingosine includes a 14-carbon non-polar tail inserted into the hydrophobic cavity of the protein, its link to hydroxy-camptothecin involves a number of polar chemical groups that interact with the aqueous environment and remain exposed in the protein-ligand complex. Our results reveal that Pru p 3 is expressed at two key times of flower and fruit development in peach, namely, during pollination and during embryo development. In both stages, the ligand of Pru p 3 is able to inhibit cell division (the ligand exhibits the anti-topoisomerase I activity characteristic of camptothecin), although with two distinct objectives: first, to inhibit a second pollination, and second, to prevent the fruit from herbivores until seed maturation.