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Insect germ warfare
Scientists identify potential target used by Pyrrhocoris apterus to eliminate bacteria
Edward R. Winstead

Insects are expert killers of bacteria. The insect kingdom flourishes in part because its species so effectively fight off bacteria. Insects lack an immune system, and researchers have long studied the mechanisms of insect germ warfare. Two strategies have been described. In one strategy, the insect host uses small proteins, or peptides, to create lethal holes in the cell membranes of bacteria. In another strategy, the peptides bind targets inside the cell, and this action somehow precipitates bacterial death.

Phyrrhocoris apterus

During the 1990s, researchers isolated antibacterial peptides in ants, bees and flies, but the binding targets were unknown. A new study identifies a potential target molecule. The research involves the beetle-like Pyrrhocoris apterus, also known as the European sap-sucking insect. American and French researchers say that Pyrrhocoris apterus targets a bacterial heat shock protein called DnaK.

Heat shock proteins are present in all cells, and one of their essential functions is to repair proteins that are misshapen due to an insult or stress. According to the researchers, the insect host uses the antimicrobial peptide to inhibit heat shock proteins. Without these proteins, bacteria cannot reproduce.

"All organisms have the mechanism for repairing misshapen proteins," says Laszlo Otvos Jr., of the Wistar Institute, in Philadelphia, who led the research. "The key to the study was showing that the DnaK binding and the bacterial killing were related events. There's no question that the peptides bind heat shock proteins, and we believe the events are positively correlated." The research appeared in a recent issue of Biochemistry.

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Otvos, L. et al. Interaction between heat shock proteins and antimicrobial peptides. Biochemistry (Published on-line October 21, 2000).

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