title: Bacillus thuringiensis Cry4Ba toxin employs two receptor-binding loops for synergistic interactions with Cyt2Aa2.
abstract: We previously demonstrated that co-expression in Escherichia coli of Bacillus thuringiensis (Bt) subsp. israelensis Cry4Ba and Bt subsp. darmstadiensis Cyt2Aa2 shows high synergistic toxicity against target mosquito larvae. Here, further insights into synergistic interactions between these two toxins were revealed through bioactivity restoration of particular inactive Cry4Ba-mutant toxins altered within the receptor-binding domain. Specific mutations at β2-β3 (Y332A) or β4-β5 (F364A) loops, but neither at three other β-hairpin loops (β6-β7, β8-β9 and β10-β11) of Cry4Ba, adversely affect toxicity restoration by Cyt2Aa2. Binding analysis using quartz crystal microbalance verified a decrease in binding of these two bioinactive-mutant toxins (Y332A and F364A) to the immobilized Cyt2Aa2. This suggests that Cry4Ba utilizes these two critical aromatic loop-residues, Tyr(332) and Phe(364), for synergistic toxicity with its alternative receptor-Cyt2Aa2.
authors.affiliation: Department of Clinical Chemistry, Faculty of Medical Technology, Mahidol University, Bangkok-noi, Bangkok, Thailand.
authors.forename: Chitsirin
authors.initials: C
authors.lastname: Lailak
authors.forename: Tararat
authors.initials: T
authors.lastname: Khaokhiew
authors.forename: Chamras
authors.initials: C
authors.lastname: Promptmas
authors.forename: Boonhiang
authors.initials: B
authors.lastname: Promdonkoy
authors.forename: Kusol
authors.initials: K
authors.lastname: Pootanakit
authors.forename: Chanan
authors.initials: C
authors.lastname: Angsuthanasombat
mesh_terms: D001413:Bacillus thuringiensis / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry*; D001665:Binding Sites; D004731:Endotoxins / Q000737:chemistry*; D006460:Hemolysin Proteins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis