Living on the Edge
How can microorganisms survive in extreme environments such as volcanic lakes or salt marshes? A giant metalloenzyme makes it possible: the heterodisulfide reductase super-assembly is found in microorganisms that produce methane from hydrogen and carbon dioxide. The super-assembly helps them adapt to changing habitats in the absence of oxygen. Using microscopic and spectroscopic methods, a team from the universities of Marburg and Potsdam succeeded in deciphering the role of the metalloenzyme in methane production. Their findings were published in the journal “Nature”.
Anaerobic microorganisms live under extreme conditions: high salt concentrations, extreme temperatures, and no oxygen. Such habitats are found not only in volcanic lakes or underground sediments, but also in the salt marshes along the German North Sea coast. There, methanogenic archaea use hydrogen (H₂) or formic acid as an electron source to reduce carbon dioxide (CO₂) to methane (CH₄). Methane is a potent greenhouse gas and contributes significantly to global warming. For this reason, understanding biological CH₄ production – methanogenesis – is particularly important for research into global carbon cycles.
A team from the universities of Marburg and Potsdam has now characterized one of the largest metalloenzymes known to date: the heterodisulfide reductase super-assembly. This molecular machine has a diameter of about 50 nanometers, making it roughly the size of a virus. The assembly comprises more than 250 protein molecules and over 600 metal compounds (“cofactors”). It links the first and last steps of methanogenesis – that is, the reduction of CO2 and the regeneration of heterodisulfide, a sulfur compound produced during CH4 production that is important for the energy metabolism of microorganisms. The large number of protein molecules and the spatial arrangement of the metal cofactors enable efficient electron transfer, allowing many reactions to proceed simultaneously.
Using cryogenic electron microscopy and infrared spectroscopy, the team deciphered the structure of the assembly and demonstrated the functional coupling of the protein molecules. “We have observed that CO2 reduction occurs exclusively in the presence of H2 and heterodisulfide,” emphasizes Max Klamke, Phd student in the group of Dr. Sven Stripp at the University of Potsdam. In addition to analyzing isolated complexes, Prof. Jan Schuller’s research group studied the enzymes using cryogenic electron tomography. “These data show that the super-complexes are present in high density within the cells and presumably play a central role in electron flow and energy storage during methanogenesis,” explains Sophia Paul, PhD student in the working group of Prof. Jan Schuller at the University of Marburg.
Architecture of the 8 MDa Hdr–Vhu–Fwd super-assembly in class I methanogens. Nature (2026)
Publication link: nature.com/articles/s41586-026-10744-9
Membrane complex aids microbes in converting CO2
So-called rock-eating microorganisms obtain their energy to convert carbon dioxide (CO2) from inorganic sources and make up the vast majority of biomass producers. Using electron microscopy and infrared spectroscopy, a research team from the universities of Potsdam and Marburg has investigated the structure of DAB2 in the sulfur bacterium Halothiobacillus neapolitanus. Their findings have been published in “Nature Communications”.
Carbon dioxide (CO2) is a component of the atmosphere and provides the essential element for all life on Earth: carbon. Autotrophic primary producers – organisms such as cyanobacteria and plants that convert CO2 into complex carbohydrates using energy from sunlight – play a key role in the conversion of CO2. This process produces biomass in the form of glucose, starch, and cellulose. Unlike primary producers, however, the majority of microorganisms do not derive their energy from sunlight but instead utilize inorganic sources such as H₂, CO₂, or various sulfur compounds. These bacteria are referred to as lithotrophic microorganisms or “rock eaters”.
When CO2 reacts with water, carbonic acid is formed, which breaks down into bicarbonate (HCO3–). CO2 spontaneously enters the bacterial cell and can also leave it again; the charged HCO3– molecule, on the other hand, cannot cross the cell membrane without an additional energy supply. Normally, the breakdown of the molecule ATP provides the energy needed to transport HCO3– into the cell, but this is not the case in lithoautotrophic microorganisms. These organisms often inhabit extreme habitats and must not waste ATP. In these organisms, the DAB2 membrane complex ensures that HCO3– is produced directly from CO2 within the cell.
The research team from Potsdam and Marburg investigated the mechanism that enables DAB2 to selectively accumulate HCO3– within the cell in an ATP-independent manner. “Using electron microscopy, we examined the structure of DAB2 from the sulfur bacterium Halothiobacillus neapolitanus and were able to show that the carbonic acid reaction described above is coupled to the concentration gradient across the cell membrane,” says Emmy Noether group leader Dr. Jan Schuller from the University of Marburg. A concentration gradient as difference in particle concentration inside and outside the cell forms across the cell membrane due to the selective accumulation of charged particles, such as protons (H+). This represents a general principle of biological energy storage.
“Based on the spectroscopic data, we have developed a theory according to which lithoautotrophic microorganisms utilize the concentration gradient across the cell membrane to catalyze an ATP-independent conversion of CO₂ to HCO3–”, adds Dr. Sven Stripp from the University of Potsdam, who leads a Heisenberg research group at the Institute of Chemistry. As a result, the energy metabolism of these microorganisms is highly efficient, enabling the rock eaters to build up biomass even under hostile conditions.
Structural basis of membrane potential coupled vectorial CO₂ hydration by the DAB2 complex in chemolithoautotrophs. Nat. Commun. (2025)
Publication link: nature.com/articles/s41586-025-08890-7
Toward Green Procedures
Methane is a powerful greenhouse gas that contributes to climate change. However, the biological conversion of carbon dioxide into methane is also considered a promising renewable energy source. In order to be able to use it for sustainable energy technologies and environmental protection, the basic mechanisms of methane formation must be better understood.
Researchers from the University of Potsdam and the Philipps University of Marburg have now made an important breakthrough in understanding the activation of an enzyme that is responsible for almost all biological methane production on Earth: methyl-coenzyme M reductase (MCR).
This enzyme contains a nickel complex that must be reduced to catalyze methane production, which is one of the most difficult redox reactions in nature. For a long time it was not clear how early life forms were able to conduct strongly reducing electrons into the enzyme. This refers to those microorganisms that have existed for billions of years and produce up to one billion tons of methane annually, so-called methanogenic archaea.
The research team led by Marburg biochemist Jan Schuller and his Potsdam colleague Sven T. Stripp have now succeeded in isolating and characterizing the MCR activation complex from a model archaeon. They discovered that it contains three uniquely coordinated and highly specialized redox cofactors, which were previously thought to occur exclusively in nitrogenase - an enzyme complex responsible for biological nitrogen fixation.
“Spectroscopy provided the final proof that the cofactors consist of iron and sulphur,” explains Sven T. Stripp. And Jan Schuller, lead author of the study, adds: “This striking similarity suggests that the systems, although they fulfill completely different functions, are evolutionarily related.” He concludes: “Ultimately, our study establishes an unprecedented evolutionary link between two fundamental biological processes: methanogenesis and nitrogen fixation.” (...)
Sven T. Stripp is currently setting up a junior research group in Potsdam with which he is researching the reaction mechanism of enzymes. “Our findings can, for example, help to produce green hydrogen or bind nitrogen from the air in order to make barren soils fertile.” Last but not least, Stripp is working on enzymes that make it possible to cleanse the atmosphere of excess carbon dioxide from the combustion of fossil fuels.
Structure of the ATP-driven methyl-coenzyme M reductase activation complex. Nature (2025).
Publication link: https://www.nature.com/articles/s41586-025-08890-7
Small but Mighty
Originally posted 2025 June 18
Hydrogen-producing enzymes are large and extremely sensitive to oxygen. This makes their use in the production of “green hydrogen” complicated. Researchers at Ruhr-Universität Bochum and the University of Potsdam have circumvented this problem: They have transferred the catalytic center of such an enzyme - the [FeFe]-hydrogenase - which is made up of iron atoms, into a ferredoxin. These small biomolecules acts as an electron carriers in all living organisms. The artificial biohybrid can efficiently produce hydrogen gas using electrons from light-driven biological systems. The researchers have published their results in the journal Advanced Science.
Hydrogen is considered to be the clean energy carrier of the future, but its sustainable production is still a major challenge. Natural enzymes, known as hydrogenases, are highly efficient hydrogen-generating biocatalysts, but their industrial use is not yet established. With 600 amino acids, they are very large and complex and usually extremely sensitive to oxygen. In addition, they require high-energy electrons, which should also be provided in an environmentally friendly way.
[FeFe]-hydrogenases use an iron-containing molecule to produce hydrogen. This so-called cofactor functions similarly to a platinum catalyst and can be chemically synthesized. However, it is inactive as an isolated molecule and requires the protein environment to achieve its maximum performance. The researchers at Ruhr-Universität Bochum wanted to simplify the highly complex hydrogenase biocatalyst to enable its integration into industrial processes. In some microalgae, hydrogenases are supplied with electrons through photosynthesis. The electron mediator is the small iron-containing protein ferredoxin, which receives the electrons directly from the light-driven photosynthetic electron transport chain.
“We asked ourselves the biologically crazy question of whether the whole thing could be shortened and the ferredoxin could form hydrogen,” explains Vera Engelbrecht, one of the two first authors of the study. And to their own great surprise, the researchers were able to identify ferredoxins that could form hydrogen in combination with the hydrogenase cofactor. “However, we had to outsmart the biological synthesis pathways,” explains Yiting She, the other first author (pictured left). "Only very specific ferredoxins were able to work together with the cofactor. Finding this out was a long but also very exciting journey."
The high activity of the biohybrid surprised the researchers . “We know that the cooperation between protein and cofactor in natural [FeFe]-hydrogenases is very important,” explains Prof. Dr. Thomas Happe, under whose leadership the project was carried out. In collaboration with Sven T. Stripp from the University of Potsdam, the new ferredoxin hydrogenase was therefore characterized spectroscopically. “It appears that the ferredoxin protein provides a chemically favorable environment for the hydrogenase catalyst,” concludes Happe. To achieve this, the ferredoxin's own natural cofactor must be replaced by the hydrogenase cofactor using complex synthesis pathways. “Despite this, the new protein can still receive electrons from photosynthesis components,” says Yiting She. This is an important feasibility study for a small artificial metalloenzyme that mimics natural light-driven hydrogenases, but with fewer components and smaller scaffolds.
Hydrogen-Producing Catalysts Based on Ferredoxin Scaffolds. Advanced Science (2025).
Publication link: https://doi.org/10.1002/advs.202501897
Early Life – Biological Methane Production Decoded
Originally posted 2025 April 17
Researchers at the Center for Synthetic Microbiology (SYNMIKRO) of Philipps-University Marburg and University of Potsdam have made a major breakthrough in understanding the activation of Methyl-coenzyme M reductase (MCR). The MCR enzyme is responsible for nearly all biological methane production and one of the most abundant enzymes on Earth. The new findings can help to understand one of nature’s oldest energy-harvesting processes and reveal an unexpected evolutionary connection between two fundamental biological processes: methane production and nitrogen fixation.
While methane is a potent greenhouse gas that contributes to climate change, the biological transformation of carbon dioxide into methane also holds great promise as a renewable energy source. Understanding the fundamental mechanisms behind methane formation could lead to advancements in sustainable energy technologies and environmental conservation.
At the heart of biological methane production – the methanogenesis – sits the enzyme MCR with its unique nickel complex F430. In order to catalyze methane production, F430 must be reduced, which is one of the most challenging redox reactions in nature. It has long remained an open question how early life forms could conduct strongly reducing electrons into the enzyme.
In their study, the research team succeeded in isolating and characterizing the MCR activation complex from the model archaeon Methanococcus maripaludis. Methanogenic archaea are microorganisms that have existed for billions of years, producing up to one billion tons of methane annually. The new electron microscopy structure now suggests that the MCR activation complex contains three uniquely coordinated and highly specialized redox cofactors that were previously thought to be exclusive to nitrogenase – an enzyme complex that is responsible for nitrogen fixation in living organisms. “The spectroscopy yielded the final piece of evidence that the cofactors are comprised of iron and sulfur”, explains Sven T. Stripp, co-author from University of Potsdam. Jan Schuller, the study’s senior author, adds: “This striking similarity suggests that, despite performing entirely different functions, these systems share an evolutionary relationship.” He concludes: “Ultimately, our study establishes an unprecedented evolutionary connection between two fundamental biological processes: methanogenesis and nitrogen fixation.”
Methanogenesis is a process that dates back to the earliest history of life on Earth, evolutionary even predating photosynthesis. It is not only responsible for methane emissions but also forms the foundation for other metabolic networks crucial for life. A deeper understanding of these mechanisms advances both our fundamental knowledge of molecular evolution and its possible biotechnological applications, ultimately aiming to mitigate methane emissions.
Structure of the ATP driven Methyl-coenzyme M reductase activation complex. Nature (2025).
Publikation link: https://www.nature.com/articles/s41586-025-08890-7
At the Interface of Biophysics and Chemistry
Originally posted 2025 January 13
Sven Stripp is a physical chemist and investigates the reaction mechanism of enzymes that convert gases such as hydrogen, nitrogen or carbon dioxide. Since December 2024, he has been setting up a new working group on “Infrared difference spectroscopy of gas-processing metal enzymes” at the University of Potsdam. The junior research group, which is funded by the Heisenberg Program of the German Research Foundation (DFG), is based at the Institute of Chemistry.
“My research aims to finally clarify the reaction mechanism of the so-called [FeFe]-hydrogenase,” says Sven Stripp. Hydrogenases are enzymes that produce, bind, and convert hydrogen. [FeFe] hydrogenases are among the metalloenzymes that play a key role in microbial energy metabolism in numerous organisms. “We use infrared spectroscopy and electrochemistry to observe the metalloenzymes at work,” he explains. The aim is to gain a better understanding of the enzymes and produce similarly active, synthetic catalysts.
“Our findings can be used, for example, to produce green hydrogen or to bind nitrogen from the air in order to make barren soils fertile,” says Stripp. He is also working on enzymes that make it possible to cleanse the atmosphere of excess carbon dioxide from the combustion of fossil fuels. “As I grew up in the Ruhr area, the latter is a particular concern of mine,” jokes Stripp. In addition to the University of Potsdam, there are close collaborations with the universities in Berlin, Bochum, and Marburg.
Sven Stripp received his doctorate in plant biochemistry (Thomas Happe) from Ruhr University Bochum in 2010 and then worked as a postdoc (Joachim Heberle) and research group leader at Freie Universität Berlin, where he habilitated in physical chemistry. Until 2024, he was visiting professor of biophysical chemistry at the Technical University Berlin.