Searching for the chemistry of life
Study shows possible new way to create DNA base pairs

Date:
October 2, 2020
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
In the search for the chemical origins of life, researchers
have found a possible alternative path for the emergence of the
characteristic DNA pattern: According to the experiments, the
characteristic DNA base pairs can form by dry heating, without
water or other solvents.



FULL STORY ==========================================================================
In the search for the chemical origins of life, researchers have found
a possible alternative path for the emergence of the characteristic DNA pattern: According to the experiments, the characteristic DNA base pairs
can form by dry heating, without water or other solvents. The team led
by Ivan Halasz from the Rudjer Boskovic Institute and Ernest Mestrovic
from the pharmaceutical company Xellia presents its observations from
DESY's X-ray source PETRA III in the journal Chemical Communications.


==========================================================================
"One of the most intriguing questions in the search for the origin of life
is how the chemical selection occurred and how the first biomolecules
formed," says Tomislav Stolar from the Rudjer Boskovic Institute in
Zagreb, the first author on the paper. While living cells control the production of biomolecules with their sophisticated machinery, the
first molecular and supramolecular building blocks of life were likely
created by pure chemistry and without enzyme catalysis. For their study,
the scientists investigated the formation of nucleobase pairs that act
as molecular recognition units in the Deoxyribonucleic Acid (DNA).

Our genetic code is stored in the DNA as a specific sequence spelled
by the nucleobases adenine (A), cytosine (C), guanine (G) and thymine
(T). The code is arranged in two long, complementary strands wound in
a double-helix structure.

In the strands, each nucleobase pairs with a complementary partner in
the other strand: adenine with thymine and cytosine with guanine.

"Only specific pairing combinations occur in the DNA, but when nucleobases
are isolated they do not like to bind to each other at all. So why
did nature choose these base pairs?" says Stolar. Investigations of
pairing of nucleobases surged after the discovery of the DNA double
helix structure by James Watson and Francis Crick in 1953. However,
it was quite surprising that there has been little success in achieving specific nucleobase pairing in conditions that could be considered as prebiotically plausible.

"We have explored a different path," reports co-author Martin Etter
from DESY.

"We have tried to find out whether the base pairs can be generated by mechanical energy or simply by heating." To this end, the team studied methylated nucleobases. Having a methyl group (-CH3) attached to the
respective nucleobases in principle allows them to form hydrogen bonds
at the Watson-Crick side of the molecule. Methylated nucleobases occur naturally in many living organisms where they fulfil a variety of
biological functions.

In the lab, the scientists tried to produce nucleobase pairs by grinding.

Powders of two nucleobases were loaded into a milling jar along with
steel balls, which served as the grinding media, while the jars were
shaken in a controlled manner. The experiment produced A:T pairs which
had also been observed by other scientists before. Grinding however,
could not achieve formation of G:C pairs.

In a second step, the researchers heated the ground cytosine and guanine powders. "At about 200 degrees Celsius, we could indeed observe the
formation of cytosine-guanine pairs," reports Stolar. In order to test
whether the bases only form the known pairs under thermal conditions, the
team repeated the experiments with mixtures of three and four nucleobases
at the P02.1 measuring station of DESY's X-ray source PETRA III. Here,
the detailed crystal structure of the mixtures could be monitored during heating and formation of new phases could be observed.

"At about 100 degrees Celsius, we were able to observe the formation
of the adenine-thymine pairs, and at about 200 degrees Celsius the
formation of Watson-Crick pairs of guanine and cytosine," says Etter,
head of the measuring station. "Any other base pair did not form even
when heated further until melting." This proves that the thermal reaction
of nucleobase pairing has the same selectivity as in the DNA.

"Our results show a possible alternative route as to how the molecular recognition patterns that we observe in the DNA could have been formed,"
adds Stolar. "The conditions of the experiment are plausible for the
young Earth that was a hot, seething cauldron with volcanoes, earthquakes, meteorite impacts and all sorts of other events. Our results open up many
new paths in the search for the chemical origins of life." The team plans
to investigate this route further with follow-up experiments at P02.1.

DESY is one of the world's leading particle accelerator centres and investigates the structure and function of matter -- from the interaction
of tiny elementary particles and the behaviour of novel nanomaterials and
vital biomolecules to the great mysteries of the universe. The particle accelerators and detectors that DESY develops and builds at its locations
in Hamburg and Zeuthen are unique research tools. They generate the most intense X-ray radiation in the world, accelerate particles to record
energies and open up new windows onto the universe. DESY is a member of
the Helmholtz Association, Germany's largest scientific association, and receives its funding from the German Federal Ministry of Education and
Research (BMBF) (90 per cent) and the German federal states of Hamburg
and Brandenburg (10 per cent).


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


========================================================================== Journal Reference:
1. Tomislav Stolar, Stipe Lukin, Martin Etter, Masa Rajić
Linarić,
Krunoslav Užarević, Ernest Mestrović, Ivan
Halasz. DNA- specific selectivity in pairing of model nucleobases
in the solid state.

Chemical Communications, 2020; DOI: 10.1039/D0CC03491F ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201002091057.htm

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