Ferritin acts as the most abundant binding protein for snowdrop lectin in the midgut of rice brown planthoppers ( Nilaparvata lugens)

Abstract

The mannose-specific snowdrop lectin [ Galanthus nivalis agglutinin (GNA)] displays toxicity to the rice brown planthopper Nilaparvata lugens. A 26 kDa GNA-binding polypeptide from N. lugens midgut was identified by lectin blotting and affinity chromatography, and characterized by N-terminal sequencing. This polypeptide is the most abundant binding protein for GNA in the N. lugens midgut. A cDNA ( fersub2) encoding this protein was isolated from an N. lugens cDNA library. The deduced amino acid sequence shows significant homology to ferritin subunits from Manduca sexta and other arthropods, plants and vertebrates, and contains a putative N-glycosylation site. Native ferritin was purified from whole insects as a protein of more than 400 kDa in size and characterized biochemically. Three subunits of 20, 26 and 27 kDa were released from the native complex. The 26 kDa subunit binds GNA, and its N-terminal sequence was identical to that of fersub2. A second cDNA ( fersub1), exhibiting strong homology with dipteran ferritin, was identified as an abundant cDNA in an N. lugens midgut-specific cDNA library, and could encode the larger ferritin subunit. The fersub1 cDNA carries a stem–loop structure (iron-responsive element) upstream from the start codon, similar to structures that have been shown to play a role in the control of ferritin synthesis in other insects.