The bilin-binding protein of Pieris brassicae. cDNA sequence and regulation of expression reveal distinct features of this insect pigment protein.

The bilin-binding protein (BBP) is a blue pigment protein which is abundant in the butterfly Pieris brassicae. In an attempt to clarify the physiological role of this member of the lipocalin family of proteins, its complete cDNA was cloned and expression of the BBP gene in P. brassicae was investigated. It was found that synthesis of the BBP mRNA is highly regulated during the insect's ontogenesis. In larvae after the third ecdysis as well as in pupae and adults, large amounts of the mRNA are present. Each of these stages itself displays a distinct time course of mRNA synthesis. In addition, BBP is expressed tissue specifically, with the fat body being the major source of this secretory protein in the larvae. Hence, the expression pattern of BBP in this organism is markedly different from the closely related pigment protein insecticyanin in Manduca sexta. Finally, the bacterial expression of BBP in a functional state was established as a basis for the future analysis of its ligand-binding functions by protein engineering.