Characterization of chemoreceptive protein binding to an oviposition stimulant using a fluorescent micro-binding assay in a butterfly.

A native female-specific chemoreceptive protein of a swallowtail butterfly [oviposition stimulant binding protein (OSBP)] was shown to specifically bind to aristolochic acid, a main stimulant for oviposition from its host plant. Oviposition stimulants are recognized by chemoreceptive organs of insects. OSBP isolated previously from the chemoreceptive organs was assumed to bind to an oviposition stimulant. Using a highly sensitive fluorescent micro-binding assay, we clarified OSBP bound to aristolochic acid. Three-dimensional molecular modeling revealed the structure of the OSBP-aristolochic acid complex. This is the first report of a native chemoreceptive protein binding to an oviposition stimulant as a ligand in insects.