Investigation on the origin of biological enzymatic catalysis

Abstract

The advent of Darwinian evolution required the emergence of molecular mechanisms for the heritable variation of fitness. One model for such a system involves populations of competing protocells, each consisting of a replicating genetic polymer encapsulated within a replicating membrane vesicle. In this model, the encapsulated genetic polymer imparts enhanced fitness to its protocell by, for example, coding for a catalyst that generates a useful metabolite. Vesicles are the best known model for testing properties of the self-assembled protocell membranes, and a model of protocell encapsulation. (Luisi, Walde et al. 1999) It is generally agreed that at the earliest stage of the prebiotic bilayer membrane formation membranes consisted of simple, long chain carboxylic acids. (Deamer, Dworkin et al. 2002) Ser-His is one of the simplest peptide catalysts, under specific conditions facilitating synthesis of peptides and RNA. (Li, Zhao et al. 2000; Gorlero, Wieczorek et al. 2009; Wieczorek, Dorr et al. 2012) The aim of this work consists in the development of experimental models to study the primitive mechanisms of Darwinian evolution. In particular, I will investigate the properties of simple fatty acid protocells that contain small catalytic peptides. First I have shown how Ser-His can catalyze synthesis of peptide nucleic acid polymer. (Gorlero, Wieczorek et al. 2009) Peptide nucleic acid is peptide bond polymer of notably achiral backbone, capable of standard Watson-Crick based pairing with natural nucleic acids. It has been proposed as a likely prebiotic precursors, or at some stages complementary genetic polymer, to natural RNA and DNA. (Egholm, Buchardt et al. 1992; Nielsen, Egholm et al. 1994; Nielsen 2007) The work presented in this thesis addresses the problem of prebiotic catalysis on the molecular polymer and the protocell level. 8 In the studies of catalytic activity of small dipeptides, I showed how prebiotic catalytic dipeptide Ser-His can catalyze synthesis of prebiotically plausible genetic polymer PNA, and how two simple catalysts, Ser-His and Ser-His-Gly can induce competition between populations of protocells. I have also showed that another simple prebiotic dipeptide, Cys-Cys, can facilitate photochemically induced division of protocell vesicles.