Oldest enzyme in cellular respiration isolated
How microbes in the primordial atmosphere obtained energy without oxygen


Date:
August 7, 2020
Source:
Goethe University Frankfurt
Summary:
Researchers have found what is perhaps the oldest enzyme in cellular
respiration. They have been able to isolate the extremely fragile
'Rnf' protein complex from the heat-loving bacterium Thermotoga
maritima. In fact, the genes that encode for the enzyme were
already discovered.

However, the researchers have now succeeded for the first time in
isolating the enzyme and thus in proving that it really is formed
by bacteria and used for energy production.



FULL STORY ==========================================================================
In the first billion years, there was no oxygen on Earth. Life developed
in an anoxic environment. Early bacteria probably obtained their energy
by breaking down various substances by means of fermentation. However,
there also seems to have been a kind of "oxygen-free respiration." This
was suggested by studies on primordial microbes that are still found in
anoxic habitats today.


==========================================================================
"We already saw ten years ago that there are genes in these microbes
that perhaps encode for a primordial respiration enzyme. Since then,
we -- as well as other groups worldwide -- have attempted to prove the existence of this respiratory enzyme and to isolate it. For a long time unsuccessfully because the complex was too fragile and fell apart at
each attempt to isolate it from the membrane. We found the fragments,
but were unable to piece them together again," explains Professor Volker Mu"ller from the Department of Molecular Microbiology and Bioenergetics
at Goethe University.

Through hard work and perseverance, his doctoral researchers Martin Kuhns
and Dragan Trifunovic then achieved a breakthrough in two successive
doctoral theses. "In our desperation, we at some point took a heat-loving bacterium, Thermotoga maritima, which grows at temperatures between
60 and 90DEGC," explains Dragan Trifunovic, who will shortly complete
his doctorate.

"Thermotoga also contains Rnf genes, and we hoped that the Rnf enzyme
in this bacterium would be a bit more stable. Over the years, we then
managed to develop a method for isolating the entire Rnf enzyme from the membrane of these bacteria." As the researchers report in their current
paper, the enzyme complex functions a bit like a pumped-storage power
plant that pumps water into a lake higher up and produces electricity
via a turbine from the water flowing back down again.

Only in the bacterial cell the Rnf enzyme (biochemical name =
ferredoxin:NAD- oxidoreductase) transports sodium ions out of the cell's interior via the cell membrane to the outside and in so doing produces an electric field. This electric field is used to drive a cellular "turbine"
(ATP synthase): It allows the sodium ions to flow back along the electric
field into the cell's interior and in so doing it obtains energy in the
form of the cellular energy currency ATP.

The biochemical proof and the bioenergetic characterization of this
primordial Rnf enzyme explains how first forms of life produced the
central energy currency ATP. The Rnf enzyme evidently functions so well
that it is still contained in many bacteria and some archaea today,
in some pathogenic bacteria as well where the role of the Rnf enzyme is
still entirely unclear.

"Our studies thus radiate far beyond the organism Thermotoga maritima
under investigation and are extremely important for bacterial physiology
in general," explains Mu"ller, adding that it is important now to
understand exactly how the Rnf enzyme works and what role the individual
parts play. "I'm happy to say that we're well on the way here, since
we're meanwhile able to produce the Rnf enzyme ourselves using genetic engineering methods," he continues.


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


========================================================================== Journal Reference:
1. Martin Kuhns, Dragan Trifunović, Harald Huber, Volker
Mu"ller. The
Rnf complex is a Na coupled respiratory enzyme in a fermenting
bacterium, Thermotoga maritima. Communications Biology, 2020; 3
(1) DOI: 10.1038/ s42003-020-01158-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200807102322.htm

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