Infectious disease: Uncovering the mechanisms of a mosquito larvicide

The structure of the bacterial toxin BinAB, a naturally occurring insecticide important in mosquito control, is reported online this week in Nature. The structure sheds light on the larvicidal function of the toxin, and the study may aid efforts to expand the potency and range of BinAB mosquito larvicides.

Mosquitoes remain among the insects most harmful to human health, spreading diseases such as malaria, dengue fever and, more recently, Zika virus. Various mosquito-control strategies are currently used, including distributing mosquito larvicides in the form of naturally occurring protein crystals, such as BinAB, which is produced by the bacterium Lysinibacillus sphaericus. BinAB is toxic to mosquito larvae but harmless to humans and other animals and is already used to control mosquito populations in the United States, Thailand, Germany and China. However, understanding of the BinAB toxin and its mode of action has been limited because the tiny size of its crystals has made solving its structure challenging.

Jacques-Philippe Colletier and colleagues used a recently developed technique called serial-femtosecond crystallography at an X-ray free-electron laser source (a powerful laser source) to solve the structure of BinAB. Their findings reveal pH-sensitive switches and carbohydrate-binding modules that may contribute to the larvicidal function of the toxin, as well as the intermolecular interactions that maintain the potency of BinAB. The study also suggests that this approach could be applied to other antimalarial and insecticidal proteins for which small crystal size is limiting structural analysis.