Closely watching over a complex soup consisting mainly of genes, Dr. Dan Tawfik adds a generous dose of oil. What emerges is a vast array of tiny suspended water droplets. It is in these droplets - holding one gene each - that he hopes to find answers to some of the most fundamental questions of life.
"What dictates natural selection and evolution?"asks Tawfik, of the Weizmann Institute's Biological Chemistry Department. "Take proteins, the basic building blocks of our body. In theory, there could exist 2050 variations of the shortest proteins we know of, not to mention the longer ones. If all possibilities were realized, the proteins would weigh more than our entire planet. How does nature choose a select few?"
The answers to these questions had been sought by scientists long before Tawfik came on the scene. Their research, however, was conducted with living cells, which posed many problems. Cells contain countless factors that could influence research results. In addition, the kinds of forces driving selection that can be tested in living cells are limited.
Tawfik, who studies enzymes (proteins that catalyze critical processes in the body), found an original solution: He constructed simplified cell models in which the only unknown is the selection process. His method, developed in collaboration with Dr. Andrew Griffiths of the Laboratory of Molecular Biology in Cambridge, England, promises to revolutionize research in this field. It enables researchers to scrutinize many billions of samples in a single experiment, compared to a mere one thousand to a million using standard techniques.
How is this done? Tawfik: First, decide what new traits your evolved enzyme should have. Then, for raw material, take an existing enzyme (without the desired traits). Make myriad copies of the gene behind the production of that enzyme, deliberately causing many mutations in the process. The logic behind this step is that at least one of the mutated genes will produce an enzyme with the desired traits. Add the supplies the genes would need to produce an enzyme and, mixing them with oil, create an emulsion (the droplets - or simplified "artificial cells"- each contain one gene and the essential supplies needed to produce an enzyme). Use a chemical process, also crafted by Tawfik, to ensure that the only genes surviving the emulsion are those that undergo mutations leading to the creation of the desired new enzyme. The others will be destroyed or washed away.
The next step is to see how the selected genes evolve. Choose the most efficient genes surviving the emulsion process and again make many copies of them, adding the supplies they need to produce an enzyme. Add oil, again producing an emulsion. Repeat the whole process of mutation and selection of the efficient genes. After many such cycles, highly evolved genes will emerge. These can direct the manufacture of fast, effective enzymes. The improvement in rate can be by a factor of many millions.
Evolution in takes
"Since this is a multistage process,"says Tawfik, "we can see evolution in the making, which is very important. Take two photos - one of a baby and another of that person as an adult - and you may not be able to tell that they are both the same person. However, if you have a series of pictures in between - of the baby developing into a young boy and then into a young man - you can link one to another and gain an understanding of how the outcome was reached."
Flexibility pays off
Some of Tawfik's findings point to a possible answer to the original question - why certain proteins are chosen over others - as it pertains to enzymes. It seems that nature may prefer enzymes that have the capacity to be jacks-of-all-trades.
Enzymes are known for their specificity - they bind to specific materials to make a product. Tawfik found, however, that some enzymes can inadvertently perform other tasks. "The tasks may not be performed with great efficiency and might not even be apparent under normal conditions, but the fact that the capability exists and could, if needed, help the organism survive, makes these enzymes preferable and provides a vital springboard for the evolution of new enzymes."
In the years to come, Tawfik's method, which mimics the great driving force of evolution, might offer the opportunity to harness nature to yield a wide range of valuable new enzymes with important applications in chemistry, biotechnology, and medicine. And, equally captivating, it might also reveal the story of evolution, enhancing our understanding of how nature's expert machinery has evolved.
Dr. Tawfik's research is supported by the Henry S. and Anne Reich Family Foundation, Washington, DC; the Estelle Funk Foundation, South El Monte, CA; Yad Hanadiv, Israel; the Harry and Jeanette Weinberg Fund for the Molecular Genetics of Cancer; and the Dolfi and Lola Ebner Center for Biomedical Research. He holds the Elaine Blond Career Development Chair.