title: Lepidopteran defence droplets - a composite physical and chemical weapon against potential predators.
abstract: Insects often release noxious substances for their defence. Larvae of Zygaena filipendulae (Lepidoptera) secrete viscous and cyanogenic glucoside-containing droplets, whose effectiveness was associated with their physical and chemical properties. The droplets glued mandibles and legs of potential predators together and immobilised them. Droplets were characterised by a matrix of an aqueous solution of glycine-rich peptides (H-WG11-NH2) with significant amounts of proteins and glucose. Among the proteins, defensive proteins such as protease inhibitors, proteases and oxidases were abundant. The neurotoxin β-cyanoalanine was also found in the droplets. Despite the presence of cyanogenic glucosides, which release toxic hydrogen cyanide after hydrolysis by a specific β-glucosidase, the only β-glucosidase identified in the droplets (ZfBGD1) was inactive against cyanogenic glucosides. Accordingly, droplets did not release hydrogen cyanide, unless they were mixed with specific β-glucosidases present in the Zygaena haemolymph. Droplets secreted onto the cuticle hardened and formed sharp crystalline-like precipitates that may act as mandible abrasives to chewing predators. Hardening followed water evaporation and formation of antiparallel β-sheets of the peptide oligomers. Consequently, after mild irritation, Zygaena larvae deter predators by viscous and hardening droplets that contain defence proteins and β-cyanoalanine. After severe injury, droplets may mix with exuding haemolymph to release hydrogen cyanide.
authors.affiliation: Plant Biochemistry Laboratory and Villum Research Center 'Plant Plasticity', Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Stefan
authors.initials: S
authors.lastname: Pentzold
authors.affiliation: Plant Biochemistry Laboratory and Villum Research Center 'Plant Plasticity', Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Mika
authors.initials: M
authors.lastname: Zagrobelny
authors.affiliation: Spectroscopy and Chemometrics, Department of Food Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Bekzod
authors.initials: B
authors.lastname: Khakimov
authors.affiliation: Spectroscopy and Chemometrics, Department of Food Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Søren Balling
authors.initials: SB
authors.lastname: Engelsen
authors.affiliation: Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine , University of Copenhagen, Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Clausen
authors.affiliation: Plant Glycobiology, Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Bent Larsen
authors.initials: BL
authors.lastname: Petersen
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark.
authors.forename: Jonas
authors.initials: J
authors.lastname: Borch
authors.affiliation: Plant Biochemistry Laboratory and Villum Research Center 'Plant Plasticity', Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark.|Carlsberg Laboratory, Copenhagen, Denmark.
authors.forename: Birger Lindberg
authors.initials: BL
authors.lastname: Møller
authors.affiliation: Plant Biochemistry Laboratory and Villum Research Center 'Plant Plasticity', Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Bak
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000032:analysis; D000818:Animals; D001000:Ants / Q000502:physiology; D012634:Bodily Secretions; D003459:Crystallins / Q000378:metabolism; D006027:Glycosides / Q000032:analysis*; D006458:Hemolymph / Q000378:metabolism*; D006856:Hydrogen Cyanide / Q000378:metabolism; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism*; D007814:Larva; D007915:Lepidoptera / Q000502:physiology*; D010446:Peptide Fragments / Q000378:metabolism*; D022142:Secretory Vesicles / Q000737:chemistry*; D013112:Spiders / Q000502:physiology; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D003459:Crystallins; D006027:Glycosides; D019476:Insect Proteins; D010446:Peptide Fragments; D006856:Hydrogen Cyanide; C004631:3-cyanoalanine; C021514:cyanogenic beta-glucosidase; D001617:beta-Glucosidase; D000409:Alanine