The untapped nitrogen reservoir

Date:
March 9, 2022
Source:
University of Konstanz
Summary:
A research team elucidates how bacteria use the compound guanidine
as a source of nitrogen.



FULL STORY ========================================================================== Guanidine is one of the most nitrogen-rich compounds. It could be a
valuable source of organic nitrogen, but only very few organisms can
access it. However, certain bacteria manage to obtain nitrogen from
guanidine. A Konstanz-based research team led by chemist Professor Jo"rg
Hartig and biologist Professor Olga Mayans has now discovered how this
works. A newly discovered enzyme plays a key role -- and, surprisingly,
so does nickel. The research results were published on 9 March 2022 in
the scientific journal Nature.


==========================================================================
No growth without nitrogen Nitrogen is an important component of
all living organisms, and no growth is possible without nitrogen
uptake. Although almost 80 percent of the atmosphere are nitrogen,
the vast majority of life forms cannot access this reserve. They are
thus dependent on chemically bound nitrogen, which is therefore also
a pivotal component of fertilisers. However, where there is not enough
nitrogen available, plants as well as many microorganisms quickly reach
their limits.

There are nitrogen reserves in nature that are barely utilized: Guanidine
is a widespread nitrogen-rich compound that excels by particularly
high chemical stability. Due to this stability, it is hardly possible
for organisms to obtain the vital nitrogen from guanidine: They cannot
"crack the nut," so to speak.

Hence, many organisms are within reach of an abundant source of nitrogen
-- and yet cannot tap it.

A Konstanz-based research network led by chemist Professor Jo"rg Hartig
and biologist Professor Olga Mayans has now identified a biochemical
mechanism that enables certain microorganisms to extract nitrogen from guanidine. In nitrate- poor environments, this is a decisive advantage
over competing organisms.

How the nitrogen mining works Cyanobacteria, also known as blue-green
algae, use an enzyme from the arginase family to initiate degradation
of guanidine in the form of hydrolysis.

Hydrolysis initially means merely the splitting of a chemical compound by water. In the case of guanidine, however, contact with water alone is not enough: "When guanidine is immersed in water, for hundreds of millennia virtually nothing will happen -- because there is not enough energy to
attack this compound," says Dr Dietmar Funck, a biologist from Konstanz.

The water therefore first needs to be "primed" in order to become
chemically more active and be able to break down the guanidine. This is
done by binding to nickel ions. The fact that, of all things, nickel is
used as the catalyst came as a surprise to the research team. "Nickel
is special. Nickel is complicated.

Very quickly you have either too little or too much of it," describes
Jo"rg Hartig: "We humans no longer have nickel-dependent enzymes in our
bodies, because it is too complicated for the organism to provide the
right amount." Nevertheless, the bacteria specifically resort to the
tricky nickel to initiate the hydrolysis. "Dealing with nickel is no
trivial matter for the bacteria either," explains biochemist Dr Malte
Sinn, "they need two auxiliary enzymes to incorporate nickel into the
enzyme." The water "primed" by nickel ions in the active centre of the
enzyme attacks the guanidine and converts it into ammonia and urea. The
urea can in turn be converted into ammonia by further enzymes.

Both compounds can thus subsequently be exploited as nitrogen sources,
making the nitrogen available for building new biomolecules.

Structural images Olga Mayans's research team carried out structural
analyses to investigate the process at the molecular level. The high specificity of the process was another surprise. The structural images
show how precisely the enzyme encloses its substrate guanidine. "It has
a very beautiful structure, strikingly symmetrical. The active site is
very small and perfect for holding the small guanidine molecule in the
correct position for hydrolysis," explains biologist Dr Jennifer Fleming
from Olga Mayans's research team.

For the research team, the current results are a first step towards understanding naturally occurring guanidine in more detail: how it is
formed, what functions it has in nature, and which other organisms can
utilize it.

Despite its wide distribution, guanidine is still a blank spot on the biochemical map.


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


========================================================================== Journal Reference:
1. D. Funck, M. Sinn, J. R. Fleming, M. Stanoppi, J. Dietrich,
R. Lo'pez-
Igual, O. Mayans, J. S. Hartig. Discovery of a Ni2 -dependent
guanidine hydrolase in bacteria. Nature, 2022; DOI:
10.1038/s41586-022-04490-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220309111123.htm

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