New role for cyanide in early Earth and search for extraterrestrial life


Date:
February 3, 2022
Source:
Scripps Research Institute
Summary:
Chemists discovered how cyanide could have enabled chemical
reactions that metabolize carbon dioxide without the complex
proteins used by living organisms today.



FULL STORY ========================================================================== Today, the colorless and deadly gas cyanide is known as a fast-acting
poison and a chemical weapon. Four billion years ago, however, it may have
been a harbinger of life. Chemists at Scripps Research have shown for the
first time how cyanide could have enabled some of the earliest metabolic reactions to create carbon-based compounds from carbon dioxide. In
addition to better understanding the evolution of life on Earth, this
discovery gives scientists insight into the potential chemistry of life
on other planets.


========================================================================== "When we look for signs of life -- either on the early Earth or on
other planets -- we base the search on the biochemistry we know exists
in life today.

The fact that these same metabolic reactions can be driven by cyanide
shows that life can be very different," says Ramanarayanan Krishnamurthy,
PhD, an associate professor of chemistry at Scripps Research, and lead
author of the new paper, published February 3, 2022 in the journal
Nature Chemistry.

Some bacteria that exist on Earth today use a series of chemical
reactions known as the reverse tricarboxylic acid cycle (r-TCA cycle)
to metabolize carbon dioxide and water into chemical compounds that are necessary for life.

Many scientists suspect that the r-TCA cycle occurred on the surface
of the early Earth to create molecules necessary for life. The only
problem: today's r-TCA cycle relies on a set of complex proteins that
wouldn't have existed before life evolved. Researchers have shown that,
in the murky primordial soup of four billion years ago, certain metals
could have driven the same reactions without today's proteins, but only
under extremely acidic and hot conditions not suspected to be prevalent
on early Earth.

Krishnamurthy and his colleagues wondered whether another molecule
might spur the same reactions under more moderate conditions. They knew
that cyanide was present in the atmosphere of the early Earth and began hypothesizing a set of reactions that could have used cyanide to produce organic molecules from carbon dioxide. Then, they tried the reactions in
a test tube. It worked -- cyanide acted in place of proteins or metals
to shuttle electrons between molecules.

"It was scary how simple it was," says Krishnamurthy. "We really didn't
have to do anything special, we mixed together these molecules, waited and
the reaction happened spontaneously." Unlike the previous r-TCA versions
that used metals, the cyanide-based cycle worked at room temperature and
in a wide pH range that reflected what would have likely been present
on the early Earth.

Moreover, the team went on to show that cyanide allowed an even simpler
version of the r-TCA cycle -- one that bypassed some of the steps, and
the less-stable intermediate molecules, in the modern cycle. This subset
of reactions could have predated the full r-TCA cycle in the emergence
of life, Krishnamurthy suggests.

There is no way of proving beyond a doubt what chemistry occurred on
the early Earth, he adds. But the discovery of the new set of reactions
allows a new set of hypothetical conditions that might be compatible
with life. And that has implications for the search for life -- in our
planet's past and elsewhere.

"It frees us up from saying there must be these metals and these extreme conditions," says Krishnamurthy. "There could be life that evolves
from this cyanide-based chemistry." This work was supported by a NASA Exobiology grant (80NSSC18K1300), the Simons Foundation (32712FY19),
and a joint grant from NSF and the NASA Astrobiology Program under the
Center for Chemical Evolution (CHE-1504217).

========================================================================== Story Source: Materials provided by Scripps_Research_Institute. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mahipal Yadav, Sunil Pulletikurti, Jayasudhan R. Yerabolu,
Ramanarayanan
Krishnamurthy. Cyanide as a primordial reductant enables a
protometabolic reductive glyoxylate pathway. Nature Chemistry,
2022; DOI: 10.1038/ s41557-021-00878-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220203122918.htm

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