Structure and Function of Hyperbranched Depsipeptides Formed Under Wet-Dry Cycling Conditions

Abstract

Proteins and peptides play a significant role in biology as structural components, enzymes, and transport carriers within cells. Peptides may have been important in prebiotic chemistry as well. In contemporary biology, peptide synthesis is achieved through highly sophisticated enzymatic machinery and energy harvesting mechanisms. However, peptide synthesis in the prebiotic world is difficult because the direct coupling of amino acids to form peptide is thermodynamically unfavourable. Also, peptides depend on their monomer sequences for folding patterns and functional properties, which is achieved by translation machinery. It is conceivable that in prebiotic chemistry, polymers other than peptides performed the necessary function. Here, we have studied polyamides formed upon condensation of polybasic carboxylic acids and amines, structures closely related to peptides, but formed under mild conditions. One of the polyamides was shown to have catalytic functions, suggesting that these structures are an attractive model for ancestral peptides. In modern biology, the peptides derive their function from sequence specificity, a property achieved through the highly evolved translation machinery. Here, we have studied the peptides and depsipeptides formed through the amide-exchange process, allowing for the insertion of amino acids into polyester matrixes. We have shown that the pattern of amino acid insertion is highly dependent on the topology of the polyesters and the chemical properties of amino acids. We, therefore, have concluded that the ester-amide exchange process could have facilitated a rudimentary “translation” in the peptide formation at the early stages of chemical evolution.