Safety considerations derived from Cry34Ab1/Cry35Ab1 structure and function.

Insecticidal proteins developed for in-plant protection against crop pests undergo extensive safety testing during the product development process. Safety considerations for insecticidal proteins expressed in crops follow recommended, science-based guidelines and specific studies are conducted on a case by case basis. Corn events expressing Bacillus thuringiensis (Bt) Cry34Ab1 and Cry35Ab1 were developed to protect maize from Diabrotica virgifera virgifera (western corn rootworm) feeding damage. The protein crystal structures of Cry34Ab1 and Cry35Ab1 are different from the more common three-domain Cry or Vip3 proteins expressed in insect resistant maize varieties. Cry34Ab1 is a single domain protein that folds into a beta sandwich structure that resembles membrane-active proteins, including several cytolysins, from a variety of natural sources. Cry35Ab1 has two domains, one domain with structural relatedness to sugar binding motifs and a second domain with an extended beta sheet structure that is clearly related to beta pore forming proteins, some of which are insecticidal, e.g. B. sphaericus BinA/BinB. In this review we discuss Cry34Ab1/Cry35Ab1 structure and function in the context of protein safety studies for insect resistant crops.