Structural and functional changes associated with cyanogen bromide treatment of wheat germ agglutinin

The lectin, wheat germ agglutinin (WGA), has been shown to have a significant larvicidal effect on the European corn borer, a major insect pest of corn. In order to characterize this toxic effect, we have undertaken structure-function studies on WGA. To this extent, the effect of cyanogen bromide (CNBr) on the conformation, subunit interactions, and biological activity of WGA has been investigated. The CNBr-modified lectin exhibits no toxicity to the ECB, cannot dimerize, does not bind to N-acetylglucosamine or its polymers, has no or vastly reduced hemagglutinating activity against red blood cells of different animals, and shows loss of an antigenic determinant by immunodiffusion. The CD spectrum of CNBr-WGA is not significantly different from that of native WGA, although the intrinsic fluorescence shows about 30% quenching. Our results suggest that the integrity of the N-terminal domain of WGA is essential for dimer formation. Furthermore, toxicity of WGA to ECB may be intrinsically related to its ability to dimerize and bind to sugar residues.