ABSTRACT
Biological evolution proceeds through competition of progeny and “survival of the ttest.” Maternal gamete cells of organisms that do not use internal fertilization are always subject to predation. Because destruction of gametes may lead to loss of genes, many invertebrates and plants have developed specic toxins that are concentrated in oocytes and seeds (respectively) to deter predators. The action of protein toxins such as ricin, abrin (from plant seeds), Shiga toxin, and cholera toxin (from bacteria) involves their targeting to specic glycan structures on the host cell surface. A toxin typically has discrete functional domains with toxic and carbohydrate-binding activities. Following the attachment of the toxin to the host target cell through its carbohydrate-binding domain, it is incorporated into and subsequently kills the cell.
