A Self-Assembled Aggregate Composed of a Fatty Acid Membrane and the Building Blocks of Biological Polymers Provides a First Step in the Emergence of Protocells.

Roy A Black,Matthew C Blosser

doi:10.3390/life6030033

Abstract

We propose that the first step in the origin of cellular life on Earth was the self-assembly of fatty acids with the building blocks of RNA and protein, resulting in a stable aggregate. This scheme provides explanations for the selection and concentration of the prebiotic components of cells; the stabilization and growth of early membranes; the catalysis of biopolymer synthesis; and the co-localization of membranes, RNA and protein. In this article, we review the evidence and rationale for the formation of the proposed aggregate: (i) the well-established phenomenon of self-assembly of fatty acids to form vesicles; (ii) our published evidence that nucleobases and sugars bind to and stabilize such vesicles; and (iii) the reasons why amino acids likely do so as well. We then explain how the conformational constraints and altered chemical environment due to binding of the components to the membrane could facilitate the formation of nucleosides, oligonucleotides and peptides. We conclude by discussing how the resulting oligomers, even if short and random, could have increased vesicle stability and growth more than their building blocks did, and how competition among these vesicles could have led to longer polymers with complex functions.

Highlights

How did prebiotic molecules on the early Earth assemble into machinery and stores of information (RNA) surrounded by a membrane? How each of these structures assembled and how they became co-localized remain unclear
We propose that such a membrane could catalyze nucleoside synthesis and facilitate the condensation reactions required for the formation of both peptides and oligonucleotides; for example, nucleoside formation in this scheme would have resulted from the joining of ribose and bases bound to a vesicle surface, rather than from reactions between compounds smaller than bases and sugars as proposed by Sutherland
To investigate whether unmodified prebiotic amino acids and dipeptides do bind to and stabilize fatty acid aggregates, we propose employing the same methods used to demonstrate interactions with nucleobases and sugars

Summary

Introduction

How did prebiotic molecules on the early Earth assemble into machinery (proteins) and stores of information (RNA) surrounded by a membrane? How each of these structures assembled and how they became co-localized remain unclear. Differential affinities provide a plausible explanation for the selection of monomers found in biopolymers, and our scheme highlights the catalytic potential of a fatty acid membrane associated with RNA and protein building blocks We propose that such a membrane could catalyze nucleoside synthesis and facilitate the condensation reactions required for the formation of both peptides and oligonucleotides; for example, nucleoside formation in this scheme would have resulted from the joining of ribose and bases bound to a vesicle surface, rather than from reactions between compounds smaller than bases and sugars as proposed by Sutherland. Formation and Stabilization of a Self-Assembled Aggregate of Prebiotic Building Blocks

Amphiphiles

Formation of Oligomers

Proteins

From an Assemblage of the Components to an Evolving Protocell

Conclusions