ABSTRACT
This chapter discusses the structure of the heterodimeric toxin ricin, aimed at serving as a guide to the rational engineering of the protein. Biochemists and medical researchers have made extensive use of both forms of protein, which we shall refer to interchangeably as ribosome-inactivating proteins or plant toxins, in the search for therapeutic agents. The structure is also vital to guide the rational design of specific genetic mutations to be created by molecular biology techniques. The linear sequence alignments were used to guide amino acid substitutions, insertions, and deletions made to the three-dimensional RTA model using an interactive graphics system. The galactosyl moiety of lactose is oriented and secured by hydrogen bonds to the side chains of several polar residues which lie at the back of the pocket, whereas the glucosyl moiety extends freely into solvent and makes no specific interaction with the protein.
