Prebiotic Formation of Catalytically Active Dipeptides via Trimetaphosphate Activation

Short peptides with unique catalytic abilities are regarded as the simplest enzymes possessing great potential as primordial species to take part in the chemical origin of life. However, prebiotic acquisition pathways of catalytically active peptides remain unclear. In this study, a microwave reactor was used to simulate hydrothermal environments, such as hydrothermal vents, either submarine or subaerial environments. A refrigerator freezer was used to make ice pieces that mimic extra-terrestrial ice crystals. Serine (Ser) and histidine (His) were used as examples, and the formation of small functional peptides involving sodium trimetaphosphate (P3 m) activation in an alkaline aqueous solution was investigated under the two typical prebiotic environments mentioned above. The obtained experimental results showed that the targeted small functional peptide Ser-His and its sequence isomer His-Ser could be formed in all simulated environments, even in the presence of disruptive amino acids, such as alanine (Ala), proline (Pro), and aspartic acid (Asp), in the reaction systems. Notably, Pro may have some effect on the chirality of the produced dipeptides by screening the configuration of the amino acids. Owing to the lack of disturbance of N-O migration in the CAPA (His) intermediate, the CAPA intermediate of His is more stable than that of Ser; therefore, His is more easily activated by P3 m to form a dipeptide with His at the N-terminal. The yield of His-Ser is at least about four times that of Ser-His in the two simulated prebiotic environments. Additionally, our work suggests that more types of amino acids can be activated simultaneously by P3 m to produce various dipeptides, which will provide abundant raw materials for the evolution of life molecules.