title: Lipid-induced conformation of helix 7 from the pore-forming domain of the Bacillus thuringiensis Cry4Ba toxin: implications for toxicity mechanism.
abstract: Helix 7 in the Cry4Ba-pore-forming domain contains conserved Tyr(249) and Phe(264) that are crucially involved in mosquito-larvicidal activity. We have now characterized lipid-induced conformation of a 27-residue Cry4Ba-alpha7 peptide in phospholipid membranes using ATR-FTIR and hydrogen/deuterium (H(+)/D(+)) exchange experiments. ATR-FTIR results showed that conformation of this peptide is influenced by lipid composition and peptide-lipid ratio. For zwitterionic membranes, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1,2-didecanoyl-sn-glycero-3-phosphocholine, the peptide adopted both alpha-helix and alpha-structure, but only alpha-helical conformation was observed in anionic membranes (1,2-dimyristoyl-sn-glycero-3-phosphoglycerol). H(+)/D(+) exchange results showed protection of approximately 90% in DMPC for beta-form, while alpha-helical form was found preferentially on membrane surface with both critical aromatic residues pointing towards bilayers. Analysis of 10-ns simulations of Cry4Ba-alpha7 in DMPC supports the stability of alpha-helical and beta-conformations for membrane-associated and membrane-inserted states, respectively. We suggest that this lipid-induced conformational change of alpha7 is conceivably related to pore-forming mechanism as structural requirement for efficient membrane insertion.
authors.affiliation: Laboratory of Molecular Biophysics and Structural Biochemistry, Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom, Thailand.
authors.forename: Kasorn
authors.initials: K
authors.lastname: Tiewsiri
authors.forename: Wolfgang B
authors.initials: WB
authors.lastname: Fischer
authors.forename: Chanan
authors.initials: C
authors.lastname: Angsuthanasombat
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000737:chemistry; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000633:toxicity; D002942:Circular Dichroism; D003198:Computer Simulation; D009033:Culicidae / Q000187:drug effects; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D004731:Endotoxins / Q000737:chemistry* / Q000633:toxicity; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000633:toxicity; D006859:Hydrogen; D007814:Larva / Q000187:drug effects; D008051:Lipid Bilayers; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010446:Peptide Fragments; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D006859:Hydrogen; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine