Researchers have, for the first time, developed a technique for directed evolution that works completely in yeast. Because yeast cells are eukaryotic, like human cells, the approach could be a powerful new way to engineer humanlike proteins and cell pathways.
In directed evolution, researchers iteratively modify genes (and their corresponding proteins) and select variants with desired improvements. It has traditionally been carried out in vitro. Applications include developing new catalysts for important chemical reactions and producing biofuels and novel therapeutics.
Scientists have just recently begun exploiting microorganisms as efficient sample vessels for directed-evolution experiments. For example, chemical biologist David R. Liu of Harvard University and coworkers devised a bacterial directed-evolution procedure called phage-assisted continuous evolution (PACE). Bacteria, however, are prokaryotes.
Now chemical biologist Virginia W. Cornish and coworkers at Columbia University have developed a technique, called heritable recombination, that exploits yeast sexual reproduction to make multiple genetic changes simultaneously and then to combine them (ACS Synth. Biol., DOI: 10.1021/sb3000904).
In heritable recombination, two separate genes, or two different parts of the same gene, are simultaneously modified iteratively, and modified yeast are screened to identify favorable changes. Mating the two modified yeast cells creates a hybrid with both alterations. Cornish and coworkers demonstrate the technique by creating a biosynthetic enzyme with mutations in three different active-site loops. The changes make it specific for substrates that the native version doesn’t recognize.
With the method, “libraries of mutants can be generated separately and their traits combined in a combinatorial fashion,” geneticist Harris H. Wang of Harvard Medical School says. “This approach is very useful in eukaryotic systems, where no such iterative technique exists today. Many potential applications of this technology exist in production of biomaterials, biofuels, pharmaceuticals, and the engineering of eukaryotic synthetic biology systems.”
Protein evolution expert Dan S. Tawfik of Weizmann Institute of Science, in Rehovot, Israel, calls heritable recombination “a powerful approach that can open exciting opportunities. In principle, it would work not only within individual proteins, as demonstrated here, but also between genes to engineer metabolic pathways, networks, and whole organisms.”