Evolving an Enzyme From a Non-Catalytic Sequence

Abstract

Life would not exist in the absence of catalysis. The “RNA World” model for the origin of life hinges on the capabilities of ribonucleic acid to encode information and perform catalysis (i.e. self-replication). Previously, functional nucleic acids such as ribozymes and deoxyribozymes (DNAzymes) have been isolated using the process of in vitro selection. This method is typically performed by isolating a catalytically active molecule from a large random library, with the assumption being that active molecules are already present in the pool and this method filters them from inactive molecules. However, in vitro selection has never been used to show that a molecule can be evolved from an inactive to an active catalyst. Here we show that the properties of DNA can be exploited to act as a proxy system for the origins of biotic chemistry by isolating a functional catalyst from a previously non-catalytic sequence. This project employs a novel perspective; rather than a random library, a known, non-functional sequence is utilized. Using in vitro selection, this known sequence is gradually evolved into a functional catalyst by solely allowing the existence of sequences that acquire mutations which enhance their function. Deep sequencing analysis of DNA pools along the evolution trajectory has identified individual mutations as the progressive drivers of molecular evolution. Evolving a catalyst from a non-catalyst gives insight into the comprehension of how life originated. This project demonstrates that an enzyme can indeed arise from a sequence of a functional polymer via permissive molecular evolution, a mechanism that may have been exploited by nature for the creation of the enormous repertoire of enzymes in the biological world today.