On Oct. 3, 2018, Frances H. Arnold, the Linus Pauling Professor of Chemical Engineering, Bioengineering and Biochemistry, was awarded the 2018 Nobel Prize in Chemistry for “the directed evolution of enzymes,” according to the award citation. Directed evolution, pioneered by Arnold in the early 1990s, is a bioengineering method for creating new and better enzymes in the laboratory using the principles of evolution. Today, the method is used in hundreds of laboratories and companies that make everything from laundry detergents to biofuels to medicines. Enzymes created with the technique have replaced toxic chemicals in many industrial processes.

Arnold shares the prize with George P. Smith of the University of Missouri in Columbia, who developed a “phage display” method for evolving proteins, and Sir Gregory P. Winter of the MRC Laboratory of Molecular Biology in Cambridge, United Kingdom, who used phage display for evolving antibodies. One half of the prize, which comes with an award of 9 million Swedish krona (about $1 million), goes to Arnold, with the other half shared by Smith and Winter.

Directed evolution works in the same way that breeders mate cats or dogs to bring out desired traits. To perform the method, scientists begin by inducing mutations to the DNA, or gene, that encodes a particular enzyme (a molecule that catalyzes, or facilitates, chemical reactions). An array of thousands of mutated enzymes is produced and then tested for a desired trait. The top-performing enzymes are selected and the process is repeated to further enhance the enzymes’ performances. For instance, in 2009, Arnold and her team engineered enzymes that break down cellulose, the main component of plant cell walls, creating better catalysts for turning agricultural wastes into fuels and chemicals.

A number of additional enzymes produced through directed evolution are now used for a host of products, including biofuels, agricultural chemicals, paper products, and pharmaceuticals. For example, the method led to a better way to produce a drug for treating type 2 diabetes.

More recently, Arnold and her colleagues used directed evolution to persuade bacteria to make chemicals not found in nature, including molecules containing silicon-carbon or boron-carbon bonds, or bicyclobutanes, which contain energy-packed carbon rings. By using bacteria, researchers can potentially make these chemical compounds in “greener” ways that are more economical and produce less toxic waste.