Were heterochiral polymers relevant in primordial and extraterrestrial life scenarios?

Agent-based simulations are employed to describe the early biological selection of oligomers made of monomers with different chirality. These simulations consider the spatial distribution of agents and resources, the balance of biomass of different chirality and the balance of chemical energy. In line with prebiotic chemical models, a disadvantage is attributed to the change in chirality within the biochemical sequence. The model includes a racemic amino acid pool, based on evidence from meteorites and Miller’s experiments. It is also assumed that the earliest life forms, being extremely primitive, were heterotrophic. Under these assumptions, the simulations show that biological sequences are not strictly homochiral but exhibit a few chirality changes. These results suggest that the current dominance of homochiral species may have been preceded by a more structurally varied biochemistry. This could be reflected in the few existing heterochiral proteins, which do not conform to the typical structures of alpha-helices or beta sheets. Alternative biochemistries might rely on such heterochiral proteins.