Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2001, 40 (18), 3310 - 3335
Evolution in a Flask
Optimization of enzymes
through genetic selection
All living organisms are subject to the slow and continuous process of evolution. In repeating cycles of mutation, selection, and duplication new characteristics accumulate within a population of organisms, giving them an advantage in the prevailing environmental conditions. Even the breeding of plants and animals with useful traits is really nothing but evolution directed by humans. "Lately, biologists and chemists have begun to go from using evolutionary strategies to change the properties of entire organisms to changing the properties of molecules," reports Donald Hilvert, a chemist at the ETH in Zurich.
How does "evolution in a flask" work, and what advantages does it have? Hilvert demonstrates with an example: together with his co-workers Sven V. Taylor and Peter Kast he has generated genetically altered strains of yeast and bacteria, which are missing an important enzyme, chorismate mutase. The enzyme catalyzes a reaction crucial for the biosynthesis of aromatic amino acids. These micro-organisms only remain alive if they are fed the missing aromatic amino acids from an external source. The researchers have smuggled randomly mutated chorismate mutase genes into these defective cells. Within a medium containing no aromatic amino acids, only those cells that have received a functional variant survive and multiply. It is thus possible to screen a very large number of mutants for functionality at once. In this way it can be determined which structural elements of the enzyme are sensitive to alterations, where the active centers of the enzyme are, and which parts are directly involved in the reaction. Important information about the relationships between the structure and function of enzymes can thus be gained.
Gaining knowledge isn’t everything, however. Evolutionary methods are also suited to the design of new enzymes. States Hilvert, "True Darwinian evolution consists of many cycles of mutation and selection. This process can be recreated in the laboratory in order to tailor the properties of an enzyme in a targeted fashion for a practical application. For example, the selectivity of an enzyme can be changed so that it will accept different substances as substrates - this is of particular interest for the enzymatic ("green") production of chemicals that are not in the repertoire of natural enzymes."