The minimotif synthesis hypothesis for the origin of life

Abstract

Several theories for the origin of life have gained widespread acceptance, led by primordial soup, chemical evolution, metabolism first, and the RNA world. However, while new and existing theories often address a key step, there is less focus on a comprehensive abiogenic continuum leading to the last universal common ancestor. Herein, I present the "minimotif synthesis" hypothesis unifying select origin of life theories with new and revised steps. The hypothesis is based on first principles, on the concept of selection over long time scales, and on a stepwise progression toward complexity. The major steps are the thermodynamically-driven origination of extant molecular specificity emerging from primordial soup leading to the rise of peptide catalysts, and a cyclic feed-forward catalytic diversification of compound and peptides in the primordial soup. This is followed by degenerate, semi-partially conservative peptide replication to pass on catalytic knowledge to progeny protocells. At some point during this progression, the emergence of RNA and selection could drive the separation of catalytic and genetic functions, allowing peptides and proteins to permeate the catalytic space, and RNA to encode higher fidelity information transfer. Translation may have emerged from RNA template driven organization and successive ligation of activated amino acids as a predecessor to translation.

Keywords: abiogenesis; chemical evolution; first principles; minimotif; natural selection; peptide.

Figure 1. Minimotif synthesis in origin of life models

A diagram of how the general parts of the minimotif synthesis hypothesis explain the gap between the primordial soup and RNA world hypotheses.

Figure 2. Minimotif synthesis model for peptide catalyst evolution from primordial soup

In Part I, stable interactions occur between compounds and amino acids, and among amino acids. The grayed figures are compounds and the colored compounds are amino acids. In Part II, peptide:compound and peptide:peptide complexes are more stable than uncomplexed peptides. Te most stable complexes, and molecules emerge out of the primordial soup. In Part III, some peptides or peptide complexes produce the first catalysts. These catalysts evolved, producing new molecules leading to new molecular interactions and new peptide interactions, and thus new catalysts in a cycle (parts III and IV).

Figure 3. Degenerate semi-conservative minimotifosome replication model and its role in prebiotic evolution

A. Minimotifosome replication. The colored figures are amino acids. The figures with a red outline are newly synthesized peptides and are connected by red lines representing new peptide bonds. A structure of a leucine zipper is an example of an extant minimotif representing what a minimotifosome may have looked like. B. Lipids and/or fatty acids form protocells encapsulating peptides, minimotifosomes, and small molecules. Those protocells with sets of minimotifs capable of template-driven reproduction provide a basis for selection and evolution. Those protocells capable of fatty acid synthesis catalyze growth of the protocell leading to spontaneous division. Division of heterogeneous protocells leads to selection and, ultimately, to the birth of the ribosome and the RNA world.