Cyt toxins produced by Bacillus thuringiensis: A protein fold conserved in several pathogenic microorganisms

Bacillus thuringiensis bacteria produce different insecticidal proteins known as Cry and Cyt toxins. Among them the Cyt toxins represent a special and interesting group of proteins. Cyt toxins are able to affect insect midgut cells but also are able to increase the insecticidal damage of certain Cry toxins. Furthermore, the Cyt toxins are able to overcome resistance to Cry toxins in mosquitoes. There is an increasing potential for the use of Cyt toxins in insect control. However, we still need to learn more about its mechanism of action in order to define it at the molecular level. In this review we summarize important aspects of Cyt toxins produced by Bacillus thuringiensis, including current knowledge of their mechanism of action against mosquitoes and also we will present a primary sequence and structural comparison with related proteins found in other pathogenic bacteria and fungus that may indicate that Cyt toxins have been selected by several pathogenic organisms to exert their virulence phenotypes.

► Cyt toxins are pore-forming toxins that affect midgut cells from dipteran insects.
► Cyt toxins synergize the toxicity of some Cry toxins by functioning as receptor for Cry toxins.
► Cyt toxins overcome resistance to Cry toxins in mosquitoes.
► N-terminal region is involved in oligomerization and C-terminal region in membrane insertion.
► Cyt toxin have similarities to related proteins from other bacteria and fungus that are pathogenic to plants or insects, a phylogenetic tree is presented.