Differential Oligomerization of Alpha versus Beta Amino Acids and Hydroxy Acids in Abiotic Proto-Peptide Synthesis Reactions

Abstract

The origin of biopolymers is a central question in origins of life research. In extant life, proteins are coded linear polymers made of a fixed set of twenty alpha-L-amino acids. It is likely that the prebiotic forerunners of proteins, or protopeptides, were more heterogenous polymers with a greater diversity of building blocks and linkage stereochemistry. To investigate a possible chemical selection for alpha versus beta amino acids in abiotic polymerization reactions, we subjected mixtures of alpha and beta hydroxy and amino acids to single-step dry-down or wet-dry cycling conditions. The resulting model protopeptide mixtures were analyzed by a variety of analytical techniques, including mass spectrometry and NMR spectroscopy. We observed that amino acids typically exhibited a higher extent of polymerization in reactions that also contained alpha hydroxy acids over beta hydroxy acids, whereas the extent of polymerization by beta amino acids was higher compared to their alpha amino acid analogs. Our results suggest that a variety of heterogenous protopeptide backbones existed during the prebiotic epoch, and that selection towards alpha backbones occurred later as a result of polymer evolution.

The Effects of Dehydration Temperature and Monomer Chirality on Primitive Polyester Synthesis and Microdroplet Assembly

“…Polyester synthesis could have been driven by wetdry cycles on early Earth in evaporative environments [14] or through precipitation and temperature cycling. [15] Mixed depsipeptide products, produced from dehydration synthesis of 𝛼HA and amino acid monomer solutions, have been shown to be produced under similar wet-dry conditions, [16,17] and some depsipeptides can perform prebiotically relevant functions such as RNA stabilization. [18] Dehydration polymerization of a wide variety of 𝛼HAs has also been shown to produce both linear [12,19] and branched [20,21] polyesters.…”

Qualitative Monitoring of Proto-Peptide Condensation by Differential FTIR Spectroscopy

“…MALDI was also hindered by the presence of minerals and salts in simulated space dust. In previous prebiotic studies on depsipeptides, amino acid conversion was typically determined by NMR. ,, Like MS, NMR analysis can be difficult in complex sample matrices. With further investigation, it is hypothesized that differential FTIR may be capable of relative quantitation of ester/amide ratios via analysis of standards with known ester and amide content, even in complex matrices.…”

Mixed anhydrides at the intersection between peptide and RNA autocatalytic sets: evolution of biological coding

“…Laboratory research has shown that RNAs alone [24] or peptides alone [25] can form self-reproducing networks. Peptides can also self-condense and recombine through wet–dry cycles, aided by thioester chemistry [26,27]. Simple amino acids such as glycine and alanine can moreover be driven by carbonyl sulfide gas into ordered amyloid fibres that in turn drive the formation of more complex structures [28].…”