Researchers isolate fragile protein complex in study of oxygen-free cellular respiration

German researchers announced the mechanism in August for what might be the world's oldest cellular "respiration."

The researchers at Johann Wolfgang Goethe University Frankfurt announced in a news release issued Aug. 7 that they had isolated "an extremely fragile protein" referred to as "Rnf" from a "heat-loving bacterium" called Thermotoga maritima.

Genes that encode for the enzyme were discovered about a decade ago but the researchers say they now have succeeded in isolating the enzyme and demonstrating that it is used to produce cellular energy in an oxygen-free environment.

"We already saw 10 years ago that there are genes in these microbes that perhaps encode for a primordial respiration enzyme," Volker Müller, Goethe University professor and head of the Department of Molecular Microbiology and Bioenergetics, said in the release. "Since then, we – as well as other groups worldwide – have attempted to prove the existence of this respiratory enzyme and to isolate it."

Earlier attempts were unsuccessful "because the complex was too fragile and fell apart at each attempt to isolate it from the membrane," Müller said in the release. "We found the fragments, but were unable to piece them together again."

It was Müller's co-authors in the study Martin Kuhns and Dragan Trifunovic, who "achieved a breakthrough" during the research, the release said.

"In our desperation, we at some point took a heat-loving bacterium, Thermotoga Maritima, which grows at temperatures between 60 and 90°C," Trifunovic said in the release. "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."

The researchers described the enzyme complex as functioning "a bit like a pumped-storage power plant." At a pumped-storage power plan water at a higher elevation produces electricity via a turbine as the water flows back down. Rnf functions similarly. Rnf transports sodium ions from the cell's interior across its membrane, which produces a high concentration of sodium ions on one side of the membrane. This gradient is used by a special turbine, Na+-F1FO ATP synthase, to form ATP, according to the release.

This research reveals an alternate system for producing energy that could have been used on early earth. Many scientists think that life evolved during the planet's first billion years despite the lack of oxygen, which meant life had to develop in an anoxic environment.

The continued existence of this system today strongly suggests it is robust and important for anoxic environments.

"Our studies thus radiate far beyond the organism Thermotoga maritima under investigation and are extremely important for bacterial physiology in general," Müller said in the release.

The research is important because we now understand how the Rnf enzyme works and what role its individual parts play, according to the release.

The research was published in the Aug. 7 edition of Nature.