Three-dimensional model of the honeybee venom allergen Api m 7: structural and functional insights

Api m 7 is one of the major protease allergens of the honeybee venom. It consists of a serine protease-like (SPL) and a CUB domain. The knowledge about the structure and function of Api m 7 is limited mainly to its amino acid sequence. Three-dimensional models of the two structural domains were constructed using their amino acid sequences and the crystallographic coordinates of prophenoloxidase-activating factor (PPAF-II) as a template for the SPL domain and the coordinates of porcine spermadhesin PSP-II for the CUB domain. The structural organization of Api m 7 suggests that the CUB domain is involved in interactions with natural substrates while the SPL domain probably activates zymogens. IgE epitopes and antigenic sites were predicted. Api m 7 shows structural and functional similarity to the members of the PPAF-II family. Possible substrates, function and evolution of the enzyme are discussed in the paper.