title: Binary Toxin Subunits of Lysinibacillus sphaericus Are Monomeric and Form Heterodimers after In Vitro Activation.
abstract: The binary toxin from Lysinibacillus sphaericus has been successfully used for controlling mosquito-transmitted diseases. An activation step shortens both subunits BinA and BinB before their interaction with membranes and internalization in midgut cells, but the precise role of this activation step is unknown. Herein, we show conclusively using three orthogonal biophysical techniques that protoxin subunits form only monomers in aqueous solution. However, in vitro activated toxins readily form heterodimers. This oligomeric state did not change after incubation of these heterodimers with detergent. These results are consistent with the evidence that maximal toxicity in mosquito larvae is achieved when the two subunits, BinA and BinB, are in a 1:1 molar ratio, and directly link proteolytic activation to heterodimerization. Formation of a heterodimer must thus be necessary for subsequent steps, e.g., interaction with membranes, or with a suitable receptor in susceptible mosquito species. Lastly, despite existing similarities between BinB C-terminal domain with domains 3 and 4 of pore-forming aerolysin, no aerolysin-like SDS-resistant heptameric oligomers were observed when the activated Bin subunits were incubated in the presence of detergents or lipidic membranes.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors.forename: Wahyu
authors.initials: W
authors.lastname: Surya
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom, Thailand.
authors.forename: Sivadatch
authors.initials: S
authors.lastname: Chooduang
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.|Persiaran Universiti, Putra Nilai, Nilai, Negeri Sembilan, Malaysia.
authors.forename: Yeu Khai
authors.initials: YK
authors.lastname: Choong
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors.forename: Jaume
authors.initials: J
authors.lastname: Torres
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom, Thailand.
authors.forename: Panadda
authors.initials: P
authors.lastname: Boonserm
mesh_terms: D001407:Bacillus / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism*; D008970:Molecular Weight; D055503:Protein Multimerization; D011994:Recombinant Proteins; D012996:Solutions; D013329:Structure-Activity Relationship
chemical_list: D001427:Bacterial Toxins; D011994:Recombinant Proteins; D012996:Solutions