Toxin lectin binding properties

The inhibition of protein synthesis in Chinese hamster cells by diphtheria toxin is antagonized by concanavalin A, succinylated concanavalin A, and wheat germ agglutinin. The effects are reversed by methyl a-D-manno-pyranoside in the first two cases and by 2-acetamido-2-deoxy-D-glucose in the last. Thus diphtheria toxin appears to have the saccharide binding properties of a lectin. 

The B-chain has lectin properties that allow it to bind to complex galactosides of cell-surface carbohydrates, while the A-chain has enzymatic activity. Binding of the B-chain to glycoside residues on glycoproteins and glycolipids appears to trigger en-docytotic uptake of the protein. Internalization of the toxin occurs, primarily via uncoated pits,3031 within a few hours the dissociation rate of ricin for I-------- -----------------------------------------1... 

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