23 February 2006

Holy Grail of Enzymatics: Making Enzymes that Make Anything You Want

Berkeley Lab, a US DOE national laboratory located near Berkeley, CA, released this news of significant progress in the intelligent design of enzymes in the lab. Ever since scientists learned they could design new genes--and thus new proteins--in the lab, they have been hoping to gain enough specificity in the design of enzymes to allow the use of artificial enzymes to create new and useful molecules that have never existed in nature. Clearly, that is nano-assembly in an enzymatic form, with potential approaching anything Eric Drexler may have dreamed for his own nanoassemblers.

In nature, the divergent evolution of promiscuous enzymes is achieved through trial and error, similar to the way in which the human immune system works. Multiple combinations of many different amino acid substitutions are tested in promiscuous enzymes until an evolutionary path that achieves a desired result is found. The amino acid substitutions that significantly drive molecular evolution are called “plasticity residues.”

The Berkeley researchers identified the plasticity residues for the Grand fir sesquiterpene synthase, then systematically recombined mutations of these residues through site-directed mutagenesis, based on a mathematical model developed by Yoshikuni. Construction of the seven sesquiterpene synthases was accomplished with the screening of fewer than 2,500 mutants. An alterative approach, called directed evolution or molecular breeding, that is currently being tested at other laboratories, requires the screening of tens of thousands to a million or more mutants.

“The enzyme synthase was there ready to be evolved, and with our methodology, we were able to rapidly and efficiently evolve it down a pathway of our choice,” Keasling said. “We are recapitulating evolution into intelligent design. In the case of this particular Grand fir enzyme synthase, it naturally makes a soup of small amounts of 52 different products. We were able to focus it instead on making large amounts of one of seven of those products.”

While the researchers have not yet reached the point where they can design a promiscuous enzyme to make any kind of product they want, even one that does not occur in nature, this demonstration represents a significant step in that direction. The idea would be to one day be able to design an enzyme synthase that would evolve along a specific functional pathway to yield a desired molecular product, then introduce it into microbes for mass production. In addition to synthesizing therapeutic drugs, other possible applications would include flavors, fragrances and nutraceuticals.

“Our ultimate goal is to be able to put as much chemistry as we can into microbes,” said Keasling, a pioneer and leading authority in the burgeoning scientific field of synthetic biology. “We can use microbes to do a lot of complicated chemistry, and the way in which this will be done is through the use of enzymes. One can imagine where you could take a series of promiscuous enzymes that would make different parts of a molecular compound, and combine them to obtain a final product that could do whatever you needed it to do.”

Since plasticity residues also play other important biological roles, in addition to the evolution of promiscuous proteins, Keasling and Yoshikuni said their technology, with some modifications, could prove useful for designing novel functions into other types of enzymes and proteins, as well as protein ligands and receptors, transcription factors and antibodies.

This research was largely funded through grants by the Bill and Melinda Gates Foundation, the National Science Foundation, and the U.S. Department of Agriculture.

Go here to read the whole report.


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