Biology subjects

Preiner, M.

Publications and source records attributed to Preiner, M..

3 recordsLinked to original sources

bioRxiv2026

Flavin cycling under prebiotic conditions: bidirectional electron transfer and versatility in nickel and iron containing environments

Flavins are organic redox cofactors central to metabolism and uniquely capable of acting as extracellular electron shuttles. For life to have emerged, it must have disengaged itself from its stationary geochemical environment, a step requiring mobile redox-active components. The role of flavins at lifes origin has been debated for decades, centered on their capacity for both one- and two-electron chemistry, distinguishing them from nicotinamides and iron-sulfur clusters. Here we chart the abiotic reduction of flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and riboflavin under hydrothermal conditions (40 {degrees}C, 1 bar N2 or 5 bar H2, pH 6, 8, and 10) by nickel (Ni) and iron (Fe). Flavins show greater environmental versatility than hydride carriers such as NAD and can harvest electrons from metals that would otherwise reduce waters protons to H2. Reduction is favoured under acidic conditions, while increasing molecular charge at higher pH impedes electron transfer. Ni acts as a hydrogenation catalyst, reducing deprotonated flavins via hydride transfer, suggesting mineral composition could have influenced geochemical selection of early electron carriers. Reduced FMNH2 and FADH2 were tested as electron shuttles toward Fe3+-containing minerals, revealing that FMNH2 enables faster mineral dissolution than FADH2. We further demonstrate complete redox cycling of FMN through Ni-assisted H2 reduction and subsequent oxidation by magnetite (Fe3O4) under inert atmosphere, releasing Fe2+. This study highlights the versatility, stability and redox chemical capabilities of flavins in prebiotic context. Significance statementHere we show how flavins, among the most evolutionarily conserved organic cofactors in biology, interact with metal surfaces under prebiotic hydrothermal conditions, and how geochemical parameters such as metal abundance and pH influence their ability to accept electrons from the environment. Flavins could serve as electron shuttles in geochemical systems that might otherwise lose their reducing power to the volatile hydrogen gas. More than that, flavins cycle through reduction and oxidation under conditions relevant to mineral-containing hydrothermal sites on the early Earth, linking the motile electron-carrying component of prebiotic chemical networks with immobile mineral environments.

biochemistry↗

bioRxiv2024

The dinucleotide structure of NAD enables specific reduction on mineral surfaces

Nucleotide-derived cofactors could function as a missing link between the informational and the metabolic part at lifes emergence. One well-known example is nicotinamide dinucleotide (NAD), one of the evolutionarily most conserved redox cofactors found in metabolism. Here, we propose that the role of these cofactors could even extend to missing links between geo- and biochemistry. We show NAD+ can be reduced under close-to nature conditions with nickel-iron-alloys found in water-rock-interaction settings rich in hydrogen (serpentinizing systems) and that nicotinamide mononucleotide (NMN), a precursor molecule to NAD, has different properties regarding reduction specificity and sensitivity than NAD. The additional adenosine monophosphate (AMP) "tail" of the dinucleotide, a shared trait between many organic cofactors, seems to play a crucial mechanistic role in preventing overreduction of the nicotinamide-bearing nucleotide. This specificity is also connected to the used transition metals. While the combination of nickel and iron promotes the reduction of NAD+ to 1,4-NADH most efficiently, in the case of NMN, the presence of nickel leads to the accumulation of overreduction products. Testing the reducing abilities of both NADH and NMNH under abiotic conditions showed that both molecules act as equally effective, soluble hydride donors in non-enzymatic, proto-metabolic stages of lifes emergence.

evolutionary biology↗

bioRxiv2019

A hydrogen dependent geochemical analogue of primordial carbon and energy metabolism

Hydrogen gas, H2, is generated in alkaline hydrothermal vents from reactions of iron containing minerals with water during a geological process called serpentinization. It has been a source of electrons and energy since there was liquid water on the early Earth, and it fuelled early anaerobic ecosystems in the Earths crust1-3. H2 is the electron donor for the most ancient route of biological CO2 fixation, the acetyl-CoA (or Wood-Ljungdahl) pathway, which unlike any other autotrophic pathway simultaneously supplies three key requirements for life: reduced carbon in the form of acetyl groups, electrons in the form of reduced ferredoxin, and ion gradients for energy conservation in the form of ATP4,5. The pathway is linear, not cyclic, it releases energy rather than requiring energy input, its enzymes are replete with primordial metal cofactors6,7, it traces to the last universal common ancestor8 and abiotic, geochemical organic syntheses resembling segments of the pathway occur in hydrothermal vents today9,10. Laboratory simulations of the acetyl-CoA pathways reactions include the nonenzymatic synthesis of thioesters from CO and methylsulfide11, the synthesis of acetate12 and pyruvate13 from CO2 using native iron or external electrochemical potentials14 as the electron source. However, a full abiotic analogue of the acetyl-CoA pathway from H2 and CO2 as it occurs in life has not been reported to date. Here we show that three hydrothermal minerals -- awaruite (Ni3Fe), magnetite (Fe3O4) and greigite (Fe3S4) -- catalyse the fixation of CO2 with H2 at 100 {degrees}C under alkaline aqueous conditions. The product spectrum includes formate (100 mM), acetate (100 M), pyruvate (10 M), methanol (100 M), and methane. With these simple catalysts, the overall exergonic reaction of the acetyl-CoA pathway is facile, shedding light on both the geochemical origin of microbial metabolism and on the nature of abiotic formate and methane synthesis in modern hydrothermal vents.

evolutionary biology↗