Binding property and activity of gloverins from the silkworm, Bombyx mori

Gloverins are inducible antibacterial glycine-rich polypeptides from lepidopteran insects. Gloverin from Hyalophora gloveri is a basic, heat-stable protein with random coil structure in solution but with α-helical structure in hydrophobic or more membrane-like environment. It has been demonstrated that gloverin inhibits the growth of Escherichia coli. Gloverin may interact with the lipid A moiety of lipopolysaccharide (LPS) by electrostatic interaction. The isoelectric points of four Bombyx mori gloverins (Bmglov1, Bmglov2, Bmglov3, Bmglov4) vary from slightly acidic to neutral, but gloverins from other insects are basic or highly basic. We aim to investigate if Bmglovs bind to LPS. Recombinant Bmglov1-4 were expressed in bacteria and purified. Plate ELISA assay showed that more Bmglovs bound to rough mutant (Ra, Rc, Rd and Re) LPS than to smooth LPS. The circular dichroism (CD) spectra showed that Bmglovs underwent conformational transitions from random coil to β-sheet and α-helix in the presence of LPS.