title: Interaction of Lysinibacillus sphaericus binary toxin with mosquito larval gut cells: Binding and internalization.
abstract: The binary toxin produced by Lysinibacillus sphaericus is composed of BinA and BinB subunits. Together, but not separately, the two subunits are highly toxic to Culex quinquefasciatus larvae, but show no toxicity to Aedes aegypti. The molecular mechanism underlying intoxication has not been clearly elucidated. The present study compares the binding and the internalization of binary toxin into the midgut epithelial cells of susceptible C. quinquefasciatus mosquito larvae with those of Bin-refractory A. aegypti. The guts from larvae fed with fluorescently labeled toxin were dissected and analyzed using a confocal laser scanning microscope. When fed with a mixture of both components, co-localization of BinA and BinB was detected both on the cell surface and in the cytoplasm of Culex larval gut cells. However, administration of BinA alone resulted in localization only on the cell membrane, whereas BinB alone was detected both on the cell membrane and inside the cytoplasm. In contrast, when a mixture of both components, or each individual component, was fed to Aedes larvae, BinA and BinB were unable to reach the cytoplasm and were localized only on the cell membrane. These results are consistent with the suggestion that the internalization of BinA is essential for toxicity, and that BinB is required for this internalization into susceptible larval gut cells.
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom 73170, Thailand.
authors.forename: Hataikarn
authors.initials: H
authors.lastname: Lekakarn
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Pahonyothin Road, Khlong Luang, Pathumthani 12120, Thailand.
authors.forename: Boonhiang
authors.initials: B
authors.lastname: Promdonkoy
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom 73170, Thailand. Electronic address: panadda.boo@mahidol.ac.th.
authors.forename: Panadda
authors.initials: P
authors.lastname: Boonserm
mesh_terms: D000818:Animals; D001406:Bacillaceae / Q000737:chemistry*; D001427:Bacterial Toxins / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport; D003465:Culex / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D019476:Insect Proteins / Q000378:metabolism / Q000502:physiology; D007814:Larva / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology
chemical_list: D001427:Bacterial Toxins; D019476:Insect Proteins; D008565:Membrane Proteins
keywords: Binary toxin; Fluorescent labeling; Internalization; Lysinibacillus sphaericus; Membrane binding; Mosquito larvae