Prebiotically Plausible Functional Compartments: A Simulation Model to Study Lipid-Peptide Protocell Dynamics

摘要

Simple amphiphilic compounds like fatty acids or isoprenoid derivatives, which have been shown to aggregate spontaneously in aqueous solution forming stable vesicles (Hargreaves & Deamer, 1978; Pozzi et al. 1996), seem better candidates as protocell components than the more complex phospholipids making up present day biological membranes. In the last years, a number of different experiments have been carried out to gain deeper knowledge on the structural and dynamic properties of this type of prebiotic compartments, as compared to standard liposomes (Chen et al. 2004; Chen & Szostak, 2004; Cheng & Luisi, 2003; Rasi et al. 2004; Nomura et al. 2001). The authors recently developed a stochastic simulation platform to study theoretically these systems (Mavelli and Ruiz-Mirazo, 2007a) and have been able to reproduce some of those experimental results (Mavelli and Ruiz-Mirazo, 2007b; forthcoming). However, the challenge for compartmentalists in the field of origins of life remains there: in order to explain why the boundary of the system plays such a fundamental role in the organization of a protometabolic network one has to search not only behind the main structural advantage of semi-permeable membranes (i.e., to maintain relevant concentration thresholds in a local environment), but also behind their functional potential (as the basic scaffolding where transport and transduction mechanisms must be anchored). Actual biomembranes have implemented really sophisticated ways to control the matter and energy flow through the system, but thanks to highly specific protein devices whose appearance is difficult to understand without the long-term action of natural selection. However, given the high prebiotic plausibility of some aminoacids (Miller, 1953), it is quite reasonable to assume that short peptide chains were available from the very beginning. So it is necessary to investigate in which way simple oligopeptides (made of alanine, glycine, serine…) could be incorporated into primitive compartments and change their properties, for sure providing new operational or regulatory capacities to the system. Despite some remarkable attempts to work in this direction (Oliver and Deamer, 1994), little has been done experimentally, so far. Using our simulation model, we will show some results that support this hypothetical ‘lipid-peptide’ protocell scenario as a worthexploring research avenue (Ruiz-Mirazo & Mavelli 2008).