Peptides Fold Into Stable Shapes in Venus’s Concentrated Sulfuric Acid

Venus’s clouds are far more chemically hostile than most environments considered in the search for life. Made up of about 98% sulfuric acid, they were long thought too corrosive for complex biological molecules to survive. A new study by researchers at MIT and collaborating institutions reports that short peptides can remain stable in concentrated sulfuric acid and adopt organized three-dimensional shapes. Peptides are short chains of amino acids and can serve as components of larger biological molecules. The researchers examined three peptides using nuclear magnetic resonance spectroscopy. The experiments showed that all three remained intact for many weeks in the highly acidic solution. The team attributes that stability in part to the scarcity of water. In a solution containing 98% sulfuric acid, there are few water molecules available for hydrolysis, a reaction that can break peptide bonds in acidic conditions. One peptide, called HHQ, normally forms flat sheets in water that can develop into long fibrils. In concentrated sulfuric acid, however, it adopted a loop resembling the Greek letter omega. Two other peptides—an extended version called HHQ13 and a separate seven-amino-acid molecule called K7—also formed omega loops. The researchers believe sulfuric acid molecules act as a structural scaffold, occupying the center of each loop and helping maintain its shape. Omega loops occur in some naturally occurring proteins, where they can connect other structural features such as sheets or helices. Their biological roles are not fully established, but defined folding is considered important because proteins generally need specific shapes to recognize targets and perform functions. Venus’s surface is too hot to be considered hospitable in the study’s context, but its cloud layer, roughly 30 to 40 miles above the surface, has milder temperatures. The findings therefore support further investigation of whether molecules entering the atmosphere—possibly including peptide building blocks delivered by meteorites—could persist there. The study does not show that Venus hosts life or that these peptides perform biological functions in the clouds. The researchers say the work instead broadens the environments scientists may need to consider. Future plans include testing longer peptides and examining whether peptide nucleic acid, a DNA-like molecule with a peptide backbone, can remain stable in a double-stranded form under similarly acidic conditions.