Functional dissection of the hexamerin receptor and its ligand arylphorin in the blowfly Calliphora vicina.

The process of receptor-mediated uptake of hexamerin storage proteins from insect haemolymph by fat body cells is a unique feature of the class Insecta. We identified the binding domains of the hexamerin receptor and the hexamerin ligand arylphorin in the blowfly, by means of the yeast-two-hybrid-system. The receptor-binding domain of arylphorin was located within domain 3 of the arylphorin monomer. The ligand-binding domain of the hexamerin receptor was mapped to the extreme N-terminus of the receptor. The binding domains identified exhibit no similarity to any functional protein domains known to date. Additionally, we identified two previously unknown protein-interactors of the hexamerin receptor. The results of this study provide further insights regarding the mechanism of the receptor-mediated endocytosis of storage proteins in insects.