1.C.106 The Bacillus thuringiensis Vegetative Insecticidal Protein-2 (Vip2) Family
Vegetative insecticidal proteins (Vip), the second generation of insecticides, are produced during the vegetative growth stage of Bacillus thuringiensis. Vips fall into three families, Vip1 (TC#1.C.42), Vip2 (this family) and Vip3 (1.C.105). They form transmembrane pores that kill the cells of the target insect (Sauka et al. 2012). Vip2 family members have been isolated from a variety of B. thuringiensis sources (Sattar and Maiti 2011; Yu et al. 2011). Vip2 proteins may have an internal duplication. Isoforms may form binary toxins that require the formation of a complex between Vip1 and Vip2 (Sattar and Maiti 2011).
ExoS and ExoT (1.C.106.4) are bi-functional type-III cytotoxins of Pseudomonas aeruginosa that share 75% identity and contain N-terminal RhoGAP domains and C-terminal ADP-ribosylation domains. The Rho GAP activities of ExoS and ExoT appear to be biochemically identical, targeting Rho, Rac, and Cdc42 (Barbieri and Sun 2004). Expression of the RhoGAP domain in mammalian cells results in the disruption of the actin cytoskeleton and interference of phagocytosis. Expression of the ADP-ribosyltransferase domain of ExoS elicits a cytotoxic phenotype in cultured cells, while expression of ExoT appears to interfere with host cell phagocytic activity. ExoS and ExoT ADP-ribosylate different substrates. While ExoS has poly-substrate specificity and can ADP-ribosylate numerous host proteins, ExoT ADP-ribosylates a more restricted subset of host proteins (Barbieri and Sun 2004).