Molecular Evolution in a Peptide-Vesicle System

Abstract

Based on a new model of a possible origin of life, we propose an efficient and stable system undergoing structural reproduction, self-optimization, and molecular evolution. This system is being formed under realistic conditions by the interaction of two cyclic processes, one of which offers vesicles as the structural environment, with the other supplying peptides from a variety of amino acids as versatile building blocks. We demonstrate that structures growing in a combination of both cycles have the potential to support their own existence, to undergo chemical and structural evolution, and to develop unpredicted functional properties. The key mechanism is the mutual stabilization of the peptides by the vesicles and of the vesicles by the peptides together with a constant production and selection of both. The development of the proposed system over time would not only represent one of the principles of life, but could also be a model for the formation of self-evolving structures ultimately leading to the first living cell. The experiment yields clear evidence for a vesicle-induced accumulation of membrane-interacting peptide which could be identified by liquid chromatography combined with high-resolution mass spectroscopy. We found that the selected peptide has an immediate effect on the vesicles, leading to (i) reduced vesicle size, (ii) increased vesicle membrane permeability, and (iii) improved thermal vesicle stability.

The Hot Spring Hypothesis for an Origin of Life

“…Szostak (2016) proposed an alternative to wet-dry cycling for the formation and replication of RNA polymers within membranous vesicles by heating and cooling in hot spring pools, possibly involving an ice-covered surface. Mayer et al (2018) investigated phase transitions of super-and subcritical CO 2 boundaries in deep tectonic fault zones as potential drivers of peptide synthesis and evolution. Perhaps most influential over the past 30 years has been the proposal that life began in seawater at hydrothermal vents (Corliss et al, 1981;Russell et al, 1993Russell and Hall, 1997Russell, 2003, 2007;Kelley et al, 2005;Lane and Martin, 2012;Barge et al, 2015Barge et al, , 2017.…”

“…It is reasonable to assume that the first functional polymers operated most effectively while bound to a protocell's membranous enclosure rather than dispersed within the dilute interior. This binding has been shown to stabilize the membrane against stresses (Black et al, 2013;Mayer et al, 2018), and would also enable sets of polymers to become more crowded on the two-dimensional surface and interact more easily. Recently, Cornell et al (2019) proposed that this colocalization sets up ''a positive feedback loop in which amino acids bind to self-assembled fatty acid membranes, resulting in membrane stabilization and leading to more binding.…”

“…A significant observation by Vlassov et al (2001) is that RNA oligomers selected by in vitro evolution can produce ion-conducting defects in lipid bilayers. Mayer et al (2018) have devised and tested a cycling protocell system operating at the phase transition between supercritical and subcritical gaseous CO 2 in deep tectonic fault zones. They have observed that oligopeptides polymerize from amino acids and selectively integrate into the bilayer structure of vesicle membranes, thereby facilitating the mutual arrangement of their protection against hydrolysis while stabilizing the surrounding vesicle.…”

Prebiotic amino acids bind to and stabilize prebiotic fatty acid membranes

“…Our focus is on molecules that are prebiotically plausible. Previous studies have shown evidence for interactions between fatty acid vesicles and nonprebiotic amino acids and peptides (23)(24)(25)(26)(27). Here, we use decanoic acid as our fatty acid rather than longer-tailed versions that produce more stable membranes but are less prebiotically plausible.…”

Life in The Context of Order and Complexity

“…In the following steps, order decreases again while complexity rises (represented by pathway 2). A similar example for an iterative approach involving pathways 1 and 2 may be seen in a co-evolution process of peptides and vesicles which was observed experimentally [37]. Here, a peptide selection process (represented by pathway 1) is followed by the formation of mixed micelles, which due to the mixing process lose their original order while gaining complexity (pathway 2).…”