Cell Compartment Stabilization in the Prebiotic Environment

Abstract

cytoskeletal proteins such as spectrin in red blood cell membranes further stabilize biological membranes (Cramer, Engelman, Von Heijne, & Rees, 1992). Stabilizing a primitive membrane is an essential first step for the self-assembly of protocells in a hydrothermal environment on the early Earth. It has been suggested that one of the first stabilizing factors in a primitive membrane would be interactions between a peptide polymer and a simplified lipid bilayer (Damer & Deamer, 2015). Each protocell is presumed to have a membranous boundary that provides an environment in which polymerization and combinatorial chemistry can occur. Without a stabilizing factor, fragile membranes can be disrupted by environmental stresses and release their contents, preventing continued synthesis and survival of nucleic acid polymers. This research is the first of its kind to tackle stabilization factors of membranes in the hydrothermal prebiotic environment. Glycine is the most abundant amino acid present in carbonaceous meteorites and was also one of the first products identified by Miller (1953) in his experiments using gas mixtures exposed to electrical discharge. Glycine is achiral with only two hydrogens on the alpha carbon and can exist in both hydrophobic and hydrophilic environments. Glycine monomers are typically incorporated in the amino acid sequences of proteins at points requiring high conformational flexibility (Oliver & Deamer, 1994). Glycine has also been demonstrated to form polymers in hydrothermal conditions (Fujioka et al., 2009). In searching for the equivalent of a prebiotic cytoskeletal polymer, we hypothesize that the conformational flexibility and INTRODUCTION Membranous enclosures are important to the development of life because they maintain systems of interacting molecules within a semi-permeable compartment. The permeable barriers of biological membranes today are composed of phospholipid bilayers with two fatty acid chains esterified to a glycerol phosphate. Because phospholipids are the product of complex metabolic processes catalyzed by enzymes, it is unlikely that they were available on prebiotic Earth, so there must have been an abiotic source of lipid-like amphiphiles (Shimoyama, Naraoka, Komiya, & Harada, 1989). Carbonaceous meteorites serve as a guide to the kinds of organic compounds likely to be present. This suite of organics includes monomers such as amino acids, nucleobases, and monocarboxylic acid meteorites. Some of the monocarboxylic acids have been shown to form membranous vesicles (Apel, Deamer, & Mautner, 2002; Namani & Deamer, 2008), which become more stable if present as a mixture with a monoglyceride or alcohol. Specialized Cell Compartment Stabilization in the Prebiotic Environment