Directed evolution makes useful enzymes
Directed evolution can be used to make enzymes with new or improved functions. Here, we describe some of the uses of these enzymes.
Enzymes have evolved over millions of years, and many enzyme variants now exist in nature. These variants catalyse a variety of reactions under different conditions. However, the ideal enzyme for commercial use is not always found in nature, so scientists are now producing enzymes with specific functions using directed evolution.
Directed evolution starts with a naturally occurring enzyme and speeds up the evolution process by introducing new genetic variation. Using this technique it is possible to develop new enzyme activities, which have never existed in nature.
Laundry detergent enzymes
Some of the first enzymes produced by directed evolution were used in laundry detergents. Laundry detergent enzymes remove stains from our clothes. To do this, the enzymes must work at high temperatures and in alkaline conditions. Most enzymes would not work well under these conditions, so directed evolution is used to help them do this.
Enzymes for cancer treatment
In David Ackerley’s lab at Victoria University, they are using directed evolution to make a bacterial enzyme for use in cancer treatment.
The enzyme is targeted to a patient’s cancer cells with a viral vector. A prodrug is then given to the patient. The enzyme activates the prodrug, which produces a toxic metabolite and kills the cancer cells. Surrounding cancer cells are also killed by the toxic metabolite in a bystander effect.
This form of gene therapy is designed to minimise side effects in the patient. The prodrug is not toxic until activated by the enzyme. The viral vector used to transfer the enzyme to the patient is modified so that it only infects cancer cells, not healthy cells. Therefore, only cancer cells will be killed by the toxic metabolite.
Other uses of evolved enzymes
- To detoxify environmental pollutants. One example is hexavalent chromium, the toxic substance involved in the Erin Brockovich case, see article at salon.com The Big Idea: Accelerated bioremediation.
- To remove the HIV virus from infected people. See article in Scientific American Designer enzyme cuts HIV out of infected cells.
- To make drug or biofuel manufacturing processes more environmentally friendly. See US company Codexis article on Green chemistry.
- To make industrial syrups, like corn syrup.
- To study how enzymes evolve naturally.
- 12 September 2008