Binding of Dipeptides to Fatty Acid Membranes Explains Their Colocalization in Protocells but Does Not Select for Them Relative to Unjoined Amino Acids.

Dipeptides, which consist of two amino acids joined by a peptide bond, have been shown to have catalytic functions. This observation leads to fundamental questions relevant to the origin of life. How could peptides have become colocalized with the first protocells? Which structural features would have determined the association of amino acids and peptides with membranes? Could the association of dipeptides with protocell membranes have driven molecular evolution, favoring dipeptides over individual amino acids? Using pulsed-field gradient nuclear magnetic resonance, we find that several prebiotic amino acids and dipeptides bind to prebiotic membranes. For amino acids, the side chains and carboxylate contribute to the interaction. For dipeptides, the extent of binding is generally less than that of the constituent amino acids, implying that other mechanisms would be necessary to drive molecular evolution. Nevertheless, our results are consistent with a scheme in which the building blocks of the biological polymers colocalized with protocells prior to the emergence of RNA and proteins.