A Note on the Evolution of Spider Toxins Containing the Ick-Motif

Most spider neurotoxins comprise a large group of structurally related polypeptides adopting the inhibitor cystine knot motif (ICK). The plethora of interesting biological functions they perform makes them worthy to study the evolutionary patterns that have been shaping their functional diversification. However, such a task remains elusive due to the lack of significant sequence similarities among the full set of spider neurotoxins. In this communication the phylogenetic relationships of a comprehensive set of spider neurotoxins with the ICK motif is analyzed by Bayesian inference. This procedure satisfactorily resolves terminal clusters, though high-order relationships remain poorly defined. Both paralogous expansion and orthologous diversification are well represented during the evolution of these ICK motif–containing peptides. Phylogenetic relationships are discussed in the light of what is known about spider neurotoxin functionalization.     

Bacillus thuringiensis Toxins: An Overview of Their Biocidal Activity

Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities.