In H2-producing hydrothermal vents, elemental palladium may have acted as a catalyst, together with phosphites, to form a range of phosphate compounds that were important for the development of early life.
Image Credit: HHU/William Martin
Scientific Frontline: Extended "At a Glance" Summary: A Geochemical Precursor of ATP
The Core Concept: Phosphite combined with catalytic amounts of palladium serves as a naturally formed inorganic geochemical precursor of adenosine triphosphate (ATP), driving primordial phosphorylation reactions in water.
Key Distinction/Mechanism: Unlike complex modern ATP synthases or inert environmental phosphate, this mechanism leverages native metal catalysts and phosphite found in hydrogen-producing hydrothermal vents to non-enzymatically phosphorylate biological molecules.
Major Frameworks/Components:
- Hydrogen-producing hydrothermal vents: Geological settings that naturally supply heat, hydrogen, phosphite, and native metal deposits.
- Native metal catalysis: The substitution of complex enzymes, such as AdpA, with shiny native metals and metal alloys (specifically palladium-iron-nickel) to catalyze reactions.
- Phosphite oxidation: The conversion of high-energy phosphite into phosphate, releasing energy to power phosphorylation.
- Broad substrate phosphorylation: The non-enzymatic phosphorylation of key biological precursors, including ribose, glucose, glycerol, and acetate.
Branch of Science: Biochemistry, Evolutionary Biology, Geochemistry, and Astrobiology.
Future Application: Inspiring novel industrial catalytic processes, green chemistry methodologies, and synthetic biology applications.
Why It Matters: It resolves the evolutionary paradox of how early cells obtained metabolic energy before complex ATP synthases evolved and explains how inert phosphate became the universal energy currency of life.
Where did the energy come from to power the chemical origin of life, and how did phosphate come to be the universal energy currency of cells? Biologists from the Institute of Molecular Evolution at Heinrich Heine University Düsseldorf (HHU) have uncovered a new and surprising source of energy that drove primordial chemical reactions on the early Earth forward to kick-start metabolism. Their findings, now published in the FEBS Journal, identify phosphite and palladium, compounds that naturally occur in H2-producing hydrothermal vents, as an inorganic precursor of ATP.
All forms of life convert environmental sources of energy into adenosine triphosphate (ATP), the universal energy currency of cells. ATP is essential to life because it provides a source of chemical energy that cells can use to make the reactions of metabolism go forward. Life requires an abundance of ATP, as two examples illustrate: A well-nourished human makes—and consumes—a body weight of ATP every day, while a tiny bacterium like Escherichia coli makes ten body weights of ATP during every cell division.
Where does all that ATP come from? Today, ATP comes from ATP synthases, molecular machines made of protein that are as universal among cells as the genetic code. ATP synthases conserve energy by converting ion gradients into rotary motion to forge ATP out of adenosine diphosphate (ADP) and phosphate. They are ancient, but they cannot be the first source of ATP. There had to be simpler precursors. But what?
Professor William Martin, head of the Institute of Molecular Evolution at HHU and senior author of the study, states, “ATP synthases are complex and evolutionarily advanced molecules; they cannot be the starting point of energy conservation at origins. Furthermore, phosphate is poorly soluble in the environment and is a very stable molecule that is generally inert; it does not want to react.”
Manon Schlikker, lead author of the study, adds, “But even the simplest forms of metabolism require phosphate as an energy currency; how did that start? We looked to the environment and microbes for clues. Many reactions of metabolism work well without enzymes, using metal catalysts that naturally occur in hydrothermal vents. In addition, many bacteria that inhabit hydrothermal vents solve the phosphate problem with phosphite, which also occurs naturally in vents. We tried that combination in the laboratory and found that some hydrothermal vent metals can activate phosphite to phosphate, and some can even phosphorylate molecules, just like ATP.”
Hydrothermal vents have been around on Earth for as long as there has been liquid water. Some scientists, including Martin and his team, think that life arose at hydrothermal vents and that traces of that origin are still preserved in the metabolism of modern cells. “Microbes that use environmental phosphite for growth convert it to phosphate with an enzyme called AdpA,” explains Schlikker. “In that reaction, AdpA phosphorylates adenosine monophosphate (AMP) to adenosine diphosphate (ADP); it conserves the energy in phosphite as a high-energy phosphate bond. Since hydrothermal vent metals are good catalysts, I tried using metals to replace the AdpA enzyme—and it worked. Metallic nickel worked, but palladium, which also occurs in vents, worked much, much better.”
Replacing enzymes with metals under hydrothermal vent conditions is a recurrent theme in the work of the HHU team. “For the past ten years, we have been investigating the ability of metals that naturally occur in hydrothermal vents, such as nickel, iron, and cobalt, to act as catalysts that can replace enzymatic functions,” says Martin. “But to replace enzymes, the metals need to be in their native state: not just some rock, but metals in their shiny, native state, like coins. H2-producing hydrothermal vents not only contain phosphite; they naturally deposit the metals in exactly that shiny state.”
That palladium catalyzed the phosphorylation of AMP to ADP with phosphite, replacing the AdpA enzyme, “was a very exciting result,” says Schlikker. “There was no literature at all on anaerobic phosphite oxidation using palladium before our work.”
The most common natural form of palladium in H2-producing hydrothermal vents is a palladium alloy with nickel and iron. To test if that form is also active, the team of Dr. Harun Tüysüz at the Max-Planck-Institut für Kohlenforschung and the IMDEA Foundation in Madrid, specialists in materials science, synthesized the palladium-iron-nickel alloy in the lab. “We were, of course, very pleased to see that it, too, catalyzed the phosphorylation reaction,” says Tüysüz.
Schlikker and colleagues then cast their experimental net more broadly to see what else the phosphite/palladium system can phosphorylate. They found that a large number of biologically relevant substrates are readily phosphorylated, including ribose, glucose, glycerol, and acetate. Acetate was particularly interesting because acetyl phosphate has long been considered a primordial currency of biochemical energy.
“What we see here,” says Martin, “is a novel and geochemically continuous route of prebiotic phosphorylation in water using a substrate and a catalyst, phosphite and palladium, that naturally occur in H2-producing hydrothermal vents.”
Tüysüz adds, “This geochemical phosphorylating chemistry is much simpler than the enzymatic route; it operates in water, and the catalyst has a very broad substrate specificity. It has all the properties expected of a truly primordial process.”
The energy that drives this phosphorylating reaction forward comes from phosphite itself. “Phosphite is a very energy-rich but very stable compound,” says Martin. “When it reacts to form phosphate, it releases more energy than ATP, but it needs a good catalyst to react. Palladium is the most effective inorganic catalyst for phosphite activation we have found so far.”
Is the hydrothermal duo of phosphite and palladium the long-sought source of phosphorylation at origins? Martin concludes, “Looking at the matter openly, phosphite plus tiny, catalytic amounts of palladium represent a naturally formed geochemical precursor of ATP. At origins, this newly recognized source of environmental energy could have provided the momentum needed to set the chemical reactions of life in motion.”
Published in journal: FEBS Journal
Title: Hydrothermal origin of metabolic phosphorylation
Authors: Manon L. Schlikker, Nadja K. Hoffmann, Sabine Metzger, Jorge Moral-Pombo, Harun Tüysüz, and William F. Martin
Source/Credit: Heinrich Heine University Düsseldorf | Arne Claussen
Edited by: Scientific Frontline
Reference Number: bchm100626_01
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