In the search for life beyond Earth, scientists have long focused on one key ingredient: liquid water. But astrobiologist Sara Seager and her team at the Massachusetts Institute of Technology aren’t convinced that water is the only solvent capable of hosting life. They have just shown that peptides—short chains of amino acids—not only survive in highly concentrated sulfuric acid but take on stable 3D conformations too (Proc. Natl. Acad. Sci. U.S.A. 2026, DOI: 10.1073/pnas.2618039123). Their findings could have implications for the search for biomolecules in Venus’s acidic clouds and beyond.
The project started with a new collaboration between Seager and the MIT chemist Mei Hong. In the years since finding phosphine signals in Venusian clouds, Seager had been working her way through the building blocks of life—nucleic acids, amino acids, and lipids—to see if any survived concentrated acid exposure. She was excited by the results; a number of these compounds are stable in the solution.
Then she hit a wall. Seager was using polarized light to try to understand the 3D structure of a synthetic analog of DNA in acid. “Then we went to small peptides to crack that,” she says. But the spectra weren’t what she expected. “We needed Mei’s expertise to figure out what was really going on.”
Hong was eager to collaborate. Her group has solved numerous protein structures using nuclear magnetic resonance (NMR) spectroscopy. Hong also had the perfect test subject: a short peptide she had analyzed in detail for a previous origins-of-life study. She says she thought, “I have the high-resolution structure [in water]. Let me put it in sulfuric acid and just see how it behaves.”
The prevailing wisdom is that peptides are incompatible with acidic solutions because acids catalyze hydrolysis of peptide bonds, thus quickly breaking the polymer chain into a slurry of amino acid links.
So it was something of a surprise when the reference peptide remained completely intact in a 98% sulfuric acid solution. Using 2D NMR, Hong determined the chain’s 3D shape. “It’s an Ω-loop in concentrated sulfuric acid, and it’s an amyloid fiber in water,” she says. And it’s stable. For two weeks, Hong’s team continued to take NMR measurements. The peptide’s spectrum never changed, indicating that the polymer’s shape was stable. Other peptide sequences followed the same trend.
Scientists at the Massachusetts Institute of Technology used nuclear magnetic resonance spectroscopy to develop a structural model of the Ω-loop 3D conformation adopted by a short peptide chain solvated by 98% sulfuric acid. Credit:
Courtesy of the researchers/Massachusetts Institute of Technology
But how could those peptides survive such a harshly acid environment?
“If you have no water, or very limited water, there’s no hydrolysis. So there’s no acid-catalyzed hydrolysis at all,” Seager says. The solution also dictates the peptide’s twisted, horseshoe-like shape. She likens the sulfuric acid to sticky tape holding the peptide residues in place through electrostatic interactions.
When the paper came across Ad Bax’s desk to review before publication, he was impressed by the findings. Bax built his career at the National Institutes of Health using NMR to study protein structures and would have expected hydrolysis to rapidly destroy peptides in such acidic solutions.
“The fact that they reported evidence for a fairly well-ordered structure for each of those peptides is quite remarkable,” he says. Though Bax can’t say what it means for the search for alien life, he thinks it’s extraordinary that any protein-like structure would be able to exist in an environment far from anything seen on Earth.
These results intrigue Stuart Bartlett, an astrobiologist who has researched prebiotic peptide structures. “This opens the door to exploring a sulfuric-acid-solvent-based biochemistry,” he says. Bartlett is interested to see what happens to the structure of longer peptides or when the scientists “just randomly scramble the sequence,” for example, to better understand if the solvent or the amino acid sequence has more influence on the final structure.
It’s possible “that there’s a lot of life out there, but it’s just hard to recognize because it’s different from life on Earth,” Bartlett says. This kind of research can help us understand the breadth of life’s possibilities, he adds.
With additional reporting by Ana Georgescu.
