An Unprecedented Biochemistry at the Origin of Life, Even on Other Worlds

A simulation program originally designed to describe surface catalysis has been used to model the chemical evolution of polymers in the earliest forms of life. The result is that, under many conditions, proteins are not entirely based on L-amino acids but rather on alternating sequences of L- and D-type amino acids. This suggests that homochirality may not be a necessary feature of life but rather a more or less accidental occurrence on our planet. The study supports this conclusion by examining natural proteins, specifically gramicidins, which are of the LD type. Their stability requires a helical folding, or secondary structure, different from the alpha-helix characteristic of nearly all known proteins.