Insecticidal crystal proteins of Bacillus thuringiensis.

The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.

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Revision of the Nomenclature for the Bacillus thuringiensis Pesticidal Crystal Proteins

The amphipathic helix, in which hydrophobia and hydrophilic residues are grouped on opposing faces, is a structural mot if found in many peptides and proteins that bind to membranes. One of the physical properties of membranes that can be altered by the binding of amphipathic helices is membrane monolayer curvature strain. Class A amphipathic helices, which are present in exchangeable plasma lipoproteins, can stabilize membranes by reducing negative monolayer curvature strain; proline-punctuated class A amphipathic helical segments are particularly effective in this regard. This property is suggested to be associated with some of the beneficial biological effects of this protein. On the other hand, lytic amphipathic helical peptides can act by increasing negative curvature strain or by forming pores composed of helical clusters. Thus, different amphipathic helical peptides can be membrane stabilizing or be lytic to membranes, depending on the structural motif of the helix, which in turn determines the nature of its association with membranes. Features of these peptides that are responsible for their specific properties are discussed. © 1994 John Wiley & Sons, Inc.

Mechanisms for the modulation of membrane bilayer properties by amphipathic helical peptides.

https://mmbr.asm.org/content/mmbr/57/4/838.full.pdf

Mosquitocidal toxins of bacilli and their genetic manipulation for effective biological control of mosquitoes.

The δ-endotoxin crystal of the mosquitocidal bacterium Bacillus thuringiensis subsp. israelensis contains four major 0-endotoxins. Expression systems were devised to synthesize each of the four toxins at concentrations at which they formed inclusion bodies in an acrystalliferous mutant of Bacillus thuringiensis. The relative activities of these inclusions were then determined against Aedes aegypti larvae. Bioassays of mixtures of the individual toxins revealed a number of synergistic interactions which explained in part why the native crystal is considerably more toxic than any of the individual toxins.

Contribution of the individual components of the δ-endotoxin crystal to the mosquitocidal activity of Bacillus thuringiensis subsp. israelensis

Bacillus thuringiensis var. israelensis δ-endotoxin: Nucleotide sequence and characterization of the transcripts in Bacillus thuringiensis and Escherichia coli☆

E.S. Ward

Papers

Bacillus thuringiensis var. israelensis δ-endotoxin: Nucleotide sequence and characterization of the transcripts in Bacillus thuringiensis and Escherichia coli☆