Scientists persuade nature to make silicon-carbon bonds

Bringing silicon to life
Artist rendering of organosilicon-based life. Organosilicon compounds contain carbon-silicon bonds. Recent research from the laboratory of Frances Arnold shows, for the first time, that bacteria can create organosilicon compounds. This does not prove that silicon- or organosilicon-based life is possible, but shows that life could be persuaded to incorporate silicon into its basic components. Credit: Lei Chen and Yan Liang (BeautyOfScience.com) for Caltech

A new study is the first to show that living organisms can be persuaded to make silicon-carbon bonds—something only chemists had done before. Scientists at Caltech "bred" a bacterial protein to make the man-made bonds—a finding that has applications in several industries.

Molecules with silicon-carbon, or organosilicon, compounds are found in pharmaceuticals as well as in many other products, including , paints, semiconductors, and computer and TV screens. Currently, these products are made synthetically, since the silicon-carbon bonds are not found in nature.

The new study demonstrates that biology can instead be used to manufacture these bonds in ways that are more environmentally friendly and potentially much less expensive.

"We decided to get nature to do what only chemists could do—only better," says Frances Arnold, Caltech's Dick and Barbara Dickinson Professor of Chemical Engineering, Bioengineering and Biochemistry, and principal investigator of the new research, published in the Nov. 24 issue of the journal Science.

The study is also the first to show that nature can adapt to incorporate silicon into carbon-based molecules, the building blocks of life. Scientists have long wondered if life on Earth could have evolved to be based on silicon instead of carbon. Science-fiction authors likewise have imagined alien worlds with silicon-based life, like the lumpy Horta creatures portrayed in an episode of the 1960s TV series Star Trek. Carbon and silicon are chemically very similar. They both can form bonds to four atoms simultaneously, making them well suited to form the long chains of molecules found in life, such as proteins and DNA.

This news video explains how Caltech researchers persuaded nature to make silicon-carbon bonds for the first time. Credit: Caltech

"No living organism is known to put silicon-carbon bonds together, even though silicon is so abundant, all around us, in rocks and all over the beach," says Jennifer Kan, a postdoctoral scholar in Arnold's lab and lead author of the new study. Silicon is the second most abundant element in Earth's crust.

The researchers used a method called directed evolution, pioneered by Arnold in the early 1990s, in which new and better enzymes are created in labs by , similar to the way that breeders modify corn, cows, or cats. Enzymes are a class of proteins that catalyze, or facilitate, chemical reactions. The directed evolution process begins with an enzyme that scientists want to enhance. The DNA coding for the enzyme is mutated in more-or-less random ways, and the resulting enzymes are tested for a desired trait. The top-performing enzyme is then mutated again, and the process is repeated until an enzyme that performs much better than the original is created.

Directed evolution has been used for years to make enzymes for household products, like detergents; and for "green" sustainable routes to making pharmaceuticals, agricultural chemicals, and fuels.

In the new study, the goal was not just to improve an enzyme's biological function but to actually persuade it to do something that it had not done before. The researchers' first step was to find a suitable candidate, an enzyme showing potential for making the silicon-carbon bonds.

"It's like breeding a racehorse," says Arnold, who is also the director of the Donna and Benjamin M. Rosen Bioengineering Center at Caltech. "A good breeder recognizes the inherent ability of a horse to become a racer and has to bring that out in successive generations. We just do it with proteins."

The structure of cytochrome c protein from Rhodothermus marinus showing iron (red) bound near the center. Researchers mutated amino acids in the region colored pink to improve the carbon-silicon bond forming ability of the protein. Credit: Frances Arnold lab/Caltech

The ideal candidate turned out to be a protein from a bacterium that grows in hot springs in Iceland. That protein, called cytochrome c, normally shuttles electrons to other proteins, but the researchers found that it also happens to act like an enzyme to create silicon-carbon bonds at low levels. The scientists then mutated the DNA coding for that protein within a region that specifies an iron-containing portion of the protein thought to be responsible for its silicon-carbon bond-forming activity. Next, they tested these mutant enzymes for their ability to make organosilicon compounds better than the original.

After only three rounds, they had created an enzyme that can selectively make silicon-carbon bonds 15 times more efficiently than the best catalyst invented by chemists. Furthermore, the is highly selective, which means that it makes fewer unwanted byproducts that have to be chemically separated out.

"This iron-based, genetically encoded catalyst is nontoxic, cheaper, and easier to modify compared to other catalysts used in chemical synthesis," says Kan. "The new reaction can also be done at room temperature and in water."

The synthetic process for making silicon-carbon bonds often uses precious metals and toxic solvents, and requires extra processing to remove unwanted byproducts, all of which add to the cost of making these compounds.

As to the question of whether life can evolve to use silicon on its own, Arnold says that is up to nature. "This study shows how quickly nature can adapt to new challenges," she says. "The DNA-encoded catalytic machinery of the cell can rapidly learn to promote new when we provide new reagents and the appropriate incentive in the form of artificial selection. Nature could have done this herself if she cared to."


Explore further

Scientists replace iron in muscle protein with non-biological metal

More information: Directed Evolution of Cytochrome c for Carbon-Silicon Bond Formation: Bringing Silicon to Life," Science, science.sciencemag.org/cgi/doi … 1126/science.aah6219
Journal information: Science

Citation: Scientists persuade nature to make silicon-carbon bonds (2016, November 24) retrieved 21 October 2019 from https://phys.org/news/2016-11-scientists-nature-silicon-carbon-bonds.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
1532 shares

Feedback to editors

User comments

Nov 25, 2016
For a moment there I got excited in thinking they actually created an enzyme with a new specificity from scratch. Instead they simply improved an existing reaction.
A prime example of how a regular solid paper destined to a specialist journal gets promoted to Science by having a Arnold/Caltech stamp on it

Nov 25, 2016
For a moment there I got excited in thinking they actually created an enzyme with a new specificity from scratch. Instead they simply improved an existing reaction.
A prime example of how a regular solid paper destined to a specialist journal gets promoted to Science by having a Arnold/Caltech stamp on it

You seem irritated.
Regardless, this was a good, informative article. The process well explained.

Nov 26, 2016
If you would be a scientist working in a non famous lab you would understand the frustration of seeing your work undervalued and theirs overvalued with all the consequences regarding career perspectives and research grants

Nov 27, 2016
If you would be a scientist working in a non famous lab you would understand the frustration of seeing your work undervalued and theirs overvalued with all the consequences regarding career perspectives and research grants

Wrong place at the wrong time...
Happens to everyone - relax and enjoy the ride...:-)

Nov 28, 2016
Wetware!!
Yeah, gonna get myself a pair of Zeiss Ikon eyes !!
http://williamgib...ive.html

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more