7
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: not found

      The alpha-5 segment of Bacillus thuringiensis delta-endotoxin: in vitro activity, ion channel formation and molecular modelling.

      Biochemical Journal
      4-Chloro-7-nitrobenzofurazan, analogs & derivatives, Amino Acid Sequence, Animals, Bacillus thuringiensis, Bacterial Proteins, chemistry, metabolism, toxicity, Bacterial Toxins, Endotoxins, Fluorescence, Fluorescent Dyes, Hemolysin Proteins, Ion Channels, biosynthesis, Lipid Bilayers, Membranes, drug effects, Models, Molecular, Molecular Sequence Data, Protein Structure, Secondary, Spodoptera

      Read this article at

      ScienceOpenPMC
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          A peptide with a sequence corresponding to the highly conserved alpha-5 segment of the Cry delta-endotoxin family (amino acids 193-215 of Bacillus thuringiensis CryIIIA [Gazit and Shai (1993) Biochemistry 32, 3429-3436]), was investigated with respect to its interaction with insect membranes, cytotoxicity in vitro towards Spodoptera frugiperda (Sf-9) cells, and its propensity to form ion channels in planar lipid membranes (PLMs). Selectively labelled analogues of alpha-5 at either the N-terminal amino acid or the epsilon-amine of its lysine, were used to monitor the interaction of the peptides with insect membranes. The fluorescent emission spectra of the 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD)-labelled alpha-5 peptides displayed a blue shift upon binding to insect (Spodoptera littoralis) mid-gut membranes, reflecting the relocation of the fluorescent probes to an environment of increased apolarity, i.e. within the lipidic constituent of the membrane. Moreover, midgut membrane-bound NBD-labelled alpha-5 peptides were protected from enzymic proteolysis. Functional characterization of alpha-5 has revealed that it is cytotoxic to Sf-9 insect cells, and that it forms ion channels in PLMs with conductances ranging from 30 to 1000 pS. A proline-substituted analogue of alpha-5 is less cytolytic and slightly more exposed to enzymic digestion. Molecular modelling utilizing simulated annealing via molecular dynamics suggests that a transbilayer pore may be formed by alpha-5 monomers that assemble to form a left-handed coiled coil of approximately parallel helices. These findings further support a role for alpha-5 in the toxic mechanism of delta-endotoxins, and assign alpha-5 as one of the transmembrane helices which form the toxic pore. The suggested role is consistent with the recent finding that cleavage of CryIVB delta-endotoxin in a loop between alpha-5 and alpha-6 is highly important for its larvicidal activity [Angsuthanasombat, Crickmore and Ellar (1993) FEMS Microbiol. Lett. 111, 255-262].

          Related collections

          Author and article information

          Comments

          Comment on this article