Using antibody catalysis to study the outcome of multiple evolutionary trials of a chemical task

Catalytic aldolase antibodies generated by immunization with two different, but structurally related, P-diketone haptens were cloned and sequenced to study similarities and differences between independently evolved catalysts. Kinetic and sequence analysis coupled with mutagenesis, structural, and mo deling studies reveal that the defining event in the evolution of these cat alysts was a somatic mutation that placed a lysine residue in a deep, yet o therwise unrefined, hydrophobic pocket. We suggest that covalent chemistrie s may be as readily selected from the immune repertoire as the traditional noncovalent interactions that have formed the basis of immunochemistry unti l this time. Further, we believe that these experiments recapitulate the de fining events in the evolution of nature's enzymes, particularly as they re late to chemical mechanism, catalytic promiscuity, and gene duplication.