Venus’s clouds are composed predominantly of sulfuric acid, and for an extended period, they were regarded as excessively corrosive for complex organic compounds. However, laboratory experiments have demonstrated the contrary. Short chains of amino acids have persisted in this environment for several weeks and have even adopted an ordered three-dimensional conformation. It is this specific structure that enables molecules to execute biological functions; consequently, such extreme conditions should not be dismissed as unfavorable in the quest for life.
An appropriate covering applied over a heated surface
Venus’s surface is heated to hundreds of degrees, and there is no question of organic matter existing there. Conversely, the cloud layer at an altitude of 48 to 64 kilometers maintains relatively moderate temperatures. It consists of droplets of sulfuric acid, which can dissolve metals and destroy most terrestrial biological molecules.
Meteorites containing peptide building blocks frequently enter the atmosphere of Venus. Whether they are capable of enduring such a hostile environment has remained unknown for an extended period.
Why does the acid not dissociate the chain?
The analysis was conducted at the Massachusetts Institute of Technology using nuclear magnetic resonance (NMR). This method is used to measure the magnetic properties of atomic nuclei and determine the structure of a molecule directly in solution. The samples remained intact for many weeks, which came as a surprise even to the researchers themselves. The study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences.
The stability observed is attributable to the lack of water. At an acid concentration of approximately 98%, nearly all free water molecules are absent. Without water, hydrolysis — the process responsible for breaking peptide bonds in an acidic milieu — does not take place. Professor Mei Hong, a distinguished chemist and senior author of the study, underscores that in the absence of water, the corrosive acid’s potency diminishes significantly.
Omega-shaped loop
One of the peptides under investigation — a synthetic HHQ comprising seven amino acids — adopts a flat beta-sheet conformation in aqueous solution, subsequently aggregating to form elongated fibrils. In concentrated acid, the identical molecule exhibits a radically different conformation, folding into a loop reminiscent of the Greek letter omega. Such omega loops are also observed in native proteins, serving as connectors between other structural motifs. Detailed information regarding the analysis is available from Phys.org.
Two additional compounds share the same structural framework: a longer variant of HHQ designated as HHQ13, and K7, which exhibits a distinctly different composition. The authors propose that the acid molecules serve as a scaffold, inserting into each loop and stabilizing it in that conformation.
The fibrils formed by HHQ in aqueous environments are of the amyloid type, and such structures are extensively recognized in terrestrial biology owing to their association with neurodegenerative diseases. The identical amino acid sequence adopts a markedly different conformation under acidic conditions; that is, the molecular shape is influenced not solely by its composition but also by the surrounding solvent environment.
Implications for the search for extraterrestrial life
Planetary scientist Sara Seager, who leads the Morning Star program, sees the result as an argument against an overly narrow search. Scientists are searching for Earth-like exoplanets, although the actual range of planetary types may turn out to be quite different. The study was co-authored by Janusz Petkowski of the Wrocław University of Technology and graduate student Jia Yi Zhang, the lead author of the article.
The subsequent phase for the group involves conducting a comprehensive study on peptide nucleic acid (PNA), a synthetic analogue of DNA characterized by a protein-like backbone in lieu of the traditional sugar-phosphate backbone. The single-stranded variant of this compound has already exhibited stability in acidic conditions; the next step is to evaluate the stability of its double-stranded form. Additionally, they will examine longer peptides independently to ascertain whether they form omega loops or other structural configurations.
