RNA-Peptide Based Coacervates as a Prebiotically Plausible Pathway towards a Proto-Ribosome
Origin of life chemistry is a multidisciplinary field focusing on the goal of understanding how Earth went from a hostile rock, inhospitable to life, to a biodiverse planet. A key goal in this is understanding how protocells formed in an abiotic environment as a pathway to the first biotic cells. A challenge presented in the emergence of cells is the existence of the ribosome, the cellular machine which translates RNA into peptides and proteins. While found in the earliest genomic history on Earth, its existence should not be compatible with an abiotic environment as enzymes are necessary to produce full-sized proteins. However, when viewed as a system and supramolecular chemistry environment, a new pathway emerges. Coacervation, a liquid-liquid phase separation event where two or more molecules undergo non-covalent interactions to form a secondary liquid phase, has been studied as a method of prebiotic compartmentalization. This thesis uses coacervates to mimic the peptide forming reaction that occurs within the peptidyl transferase centre of the ribosome. To begin with an appropriate coacervate environment was found through the study of prebiotically a plausible peptide FRGRGRGA against the microRNA’s, A-10 and U-10 as well as their polymeric analogues, poly-A and poly-U. These biomacromolecules were in a variety of chemical environments, including against acidic, neutral and basic conditions to test their ability to undergo coacervation and maintain their assemblies. Coacervate formation was tested in the presence of excess RNA and excess peptide and in general, systems showed greater supramolecular assembly when excess peptide was available. Coacervate systems containing microRNAs were studied via HPLC to test their competitive preference to enter the condensed phase when both RNAs were available. This showed quantitatively that uptake of A-10 into the condensed phase was preferred to U-10, providing information on the base discrimination in liquid-liquid phase separation. RNA-L-phenylalanine conjugates: AMP-2’/3’-L-Phe¸ [A-10]-2’/3’-L-Phe and [U-10]-2’/3’-L-Phe, was achieved to understand their formation in a coacervate free environment and to provide standards for analytical studies. The final stage of this thesis explores the conditions in which peptide elongation can occur on an RNA strand, specifically looking at how this reaction is facilitated by coacervates, therefore providing a prebiotically plausible mechanism for aminoacylation.
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