Directed evolution

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Directed evolution is a method used in protein engineering to harness the power of Darwinian selection to evolve proteins or RNA with desirable properties not found in nature.

A typical directed evolution experiment involves two steps:

1. Library creation: The gene encoding the protein of interest is mutated and/or recombined at random to create a large library of gene variants. Techniques commonly used in this step are error-prone PCR and DNA shuffling.
2. Library screening or selection: The library is screened by a high-throughput assay or subjected to selection in a cell to identify mutants (= variants) that possess the desired properties. Selected mutants that are identified in this way then have their DNA sequenced to understand what mutations have occurred.

The evolved protein is then characterized using biochemical methods.

This approach is an alternative to site-directed mutagenesis based on X-ray crystallography data.

Most directed evolution projects seek to evolve properties that are useful to humans in an agricultural, medical or industrial context. It is thus possible to use this method to optimize properties that were not selected for in the original organism. This may include catalytic specificity, thermostability and many others.

[edit] External links

• The Frances H. Arnold Research Group, a directed evolution laboratory

[edit] Further reading

• Otten, L. G. and Quax, W. J. (2005) "Directed evolution: selecting today's biocatalysts." Biomol Eng 22 1-9

• Besenmatter W., Kast P. and Hilvert D. (2004) "New Enzymes from Combinatorial Library Modules." Methods in Enzymology 388 91-102

• Stemmer, W. P. (1994) "Rapid evolution of a protein in vitro by DNA shuffling." Nature 370 389-391

• Arnold, F. H. (1998). "Design by directed evolution." Accounts of Chemical Research 31 125-131.