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Enzyme links up carbon and silicon: selective breeding enables biological bonding of the atoms.

Carbon and silicon don't play nice in nature--they link up only in human-made products like paint and pharmaceuticals. But just three generations of selective breeding of a microbe yielded an enzyme that brings the two atoms together, scientists report in the Nov. 25 Science. It's the first time biological tools have bonded carbon to silicon, perhaps opening a way to let organisms build proteins and other molecules with silicon.

"What excites me is the demonstration of how rapidly biological systems can innovate," says Frances Arnold, a chemical engineer at Caltech. "They can create new chemistry, new catalytic capabilities out of what's already there."

Enzymes are biological catalysts--they kick-start chemical reactions inside living organisms. For instance, cytochrome c shuffles electrons around to help cells make energy. In the new study, Arnold, chemical engineer Jennifer Kan and their Caltech colleagues discovered that cytochrome c from hot spring-dwelling Rhodothermus marinus bacteria had an untapped potential for forging carbon-silicon bonds.

To improve on that limited capability, the team introduced mutations into A marinus' DNA and picked out the bacteria making the most catalytically active cytochrome c. After three rounds of mutations, the team was left with a finalist that could jump-start the formation of carbon-silicon bonds more than 15 times better than the top synthetic catalysts used for the reaction.

Carbon-silicon bonds are found in hundreds of products. So the enzyme-based catalyst might someday offer a more sustainable alternative to the expensive metal catalysts that are now used to create these compounds.

But first the enzyme might need additional tweaking. "The caveat is the particular carbon-silicon bond being made," says John Hartwig, an organic chemist at the University of California, Berkeley. The specific silicon-containing compounds made by the enzyme aren't widely produced by chemical companies --although the compounds could be intermediate steps in other reactions.

The study also opens up a way to let simple organisms like bacteria use silicon as a building block, which could change their behavior in ways scientists have never been able to study. "We can think about the effects of having silicon there," Arnold says. "In the past, that's been hard to do."

Caption: With an alteration to the part of the enzyme shown in pink, this cytochrome c's ability to bond carbon and silicon improved.

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Title Annotation:MATTER & ENERGY
Author:Hamers, Laurel
Publication:Science News
Geographic Code:1USA
Date:Dec 24, 2016
Words:388
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