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How to make silicon life

Bacterial protein taught to combine the carbon with silicon.

Life on earth is often called carbon. The special chemical properties of carbon allow it to make him the long chain molecules, including branched, but if we look at the molecules of proteins, nucleic acids and lipids, then these circuits and see – mainly carbon, although other atoms.


The structure of one of the artificial organosilicon compounds under a microscope. (Photo: R. Tanaka / Flickr.com.)

Bacteria Rhodothermus marinus, whose protein is modified to work with silicon. (Photo: Microbewiki.) ”

But carbon is not the only one – it is very similar to silicon, which also in the earth’s crust is 150 times greater than carbon (silicon generally one of the most abundant elements in the Universe) . Moreover, although life on Earth and went by the way of carbon, some living organisms silicon is not neglected: it is needed by the plants as a factor of fertility (in animal cells, it is even possible to find fatality – microscopic particles of silicon dioxide SiO2), and diatoms of the same silica used for the construction of a protective shell.

However, biomolecules of silicon no. Chemists, of course, long ago learned to synthesize carbon-silicon molecules such silicones can be found in pharmaceuticals, among dyes, sealers, herbicides, etc. But, again, in living organisms, no enzymes that could manipulate silicon compounds.

And here employees of the California Institute of technology, this enzyme failed to do. Francis Arnold (Francis H. Arnold) and her colleagues used an evolutionary approach, that is first they of the variety of proteins found those who in principle could work with silicon, and then began to make these molecules more or less random mutations. Due to mutations in the protein change the amino acid sequence, and therefore, changing the properties of the whole protein molecule, including its propensity to work with a particular chemical substrate. After each mutation proteins were examined on the subject of how they relate to silicon.

In the experiment initially “participated” not absolutely all of the enzymes that can be found in nature, and those that contain a chemical group called heme. The most well-known heme-containing protein hemoglobin, which carries oxygen. But there are also quite a lot of proteins that use heme to perform chemical reactions: Gema signed an iron atom, and not just because of the iron, which in Gema easily accepts and donates electrons, the manipulation of chemical bonds become much easier with the physico-chemical point of view.

The important role of proteins with heme play in the respiratory chain of mitochondria. Recall that the essence of the respiratory chain to oxidize any organic molecule, and the resulting energy to conclude in a convenient form, cells; oxidation takes place quite difficult and with the participation of several proteins, among which the lion’s share of work performed by the heme-containing cytochromes.

As a result of artificial evolution, which had to do protein molecules capable of working with silicon, has the lead a protein called cytochrome from the bacterium Rhodothermus marinus. The article in Science says that this cytochrome had quite a bit of mutations to use heme and iron in it to learn how to create a chemical bond between carbon and silicon; and its efficiency was fifteen times higher than the best method of chemical synthesis, used for the same purpose. The modified cytochrome C synthesized twenty different carbon-silicon compounds, nineteen of which chemists still could imagine except in theory.

But all of this cytochrome was done, so to speak, in a test tube, but what about this cage? When the gene of this protein, introduced into DNA of E. coli, it was found that cytochrome it works the same as in the reaction mixture: in the cells of E. coli appeared carbon-silicon compounds. When you consider that for new features squirrel took a lot of mutations, it is possible to imagine that one day the earth bacteria will learn to use the silicon, and then silicon (or silicone) the life of science fiction and the astrobiologists are looking for on other planets, will bloom in our backyard.

On the other hand, silicon life after all is still why on Earth has flourished, although silicon there is more than enough. It is assumed that it happened because silicon, despite all its similarity with carbon, still has the same as the carbon, plasticity in the formation of chemical bonds with other elements, so that the potential variety of silicone biomolecules is not so great.

Perhaps the new enzyme will help to experimentally test this hypothesis. What to more mundane matters, the authors believe that the modified cytochrome (or some other similar proteins) useful in the production of organosilicon compounds – especially as unwanted by-products he has produced quite a bit.

According to LiveScience.

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