4.2 Chemical and Genetic Mutation of Enzymes for Creating Novel Catalysts

Gene technique as well as semisynthesis usually handles naturally occurring proteins. On the other hand, artificial proteins with completely new primary sequences have been successfully constructed by chemical synthesis. Mutations at positions 156 and 166 produced changes in k_cat/K_m toward glutamate, glutamine, methionine, and lysine P1 substrates of up to 4000, 60, 200, and 80 times, respectively. The three-dimensional atomic structures of yeast iso-1 -cytochrome c and the Ser 87 mutant protein have been elucidated. Replacement of Phe 87 with a serine residue resulted in conformational changes both near and remote from the mutation site. Mutation of a protein usually causes the following changes in the protein: loss of interactions from the original side chain, gain of modified interactions from the new side chain, and structural reorganization, which may be local or propagated elsewhere in the protein.