Membranes Composed of Lipopeptides and Liponucleobases Inspired Protolife Evolution.

Abstract

Amino acids and peptides have been demonstrated to form lipoamino acids and lipopeptides under presumed prebiotic conditions, and readily form liposomes. Of the common nucleobases, adenine forms a liponucleobase even below 100 °C. Adenine as well as other nucleobases can also be derivatized with ethylene carbonate (and likely other similar compounds) onto which fatty acids can be attached. The fatty acid tails along with appropriately functionalized nucleobases provide some solubility of liponucleobases in membranes. Such membranes would provide a structure in which three of biology's major components are closely associated and available for chemical interactions. Nucleobase-to-nucleobase interactions would ensure that the liponucleobases would have a uniquely different head-group relationship than other amphiphiles within a membrane, likely forming rafts due their π-π interactions and providing surface discontinuities that could serve as catalytic sites. The π-π bond distance in aromatic compounds is typically 0.34 nm, commensurate with that of the amine to carboxylate distance in alpha amino acids. This would have provided opportunity for hydrogen bonding between amino acids and the distal primary amines or tautomeric carbonyl/hydroxyl groups of two π-bonded nucleobases. Such bonding would weaken the covalent linkages within the amino acids, making them susceptible to forming peptide bonds with an adjacent amino acid, likely a lipoamino acid or lipopeptide. Were this second lipoamino acid bound to a third π-bonded nucleobase, it could result in orientation, destabilization and peptide formation. The stacked triplet of nucleobases might constitute the primordial codon triplet from which peptides were synthesized: primordial translation.