Projet ANR-06-BLAN-0151 – Prebio-Lipid : Prebiotic lipids from carbon oxides and H2S at hydrothermal vents. Investigation by laboratory simulation experiments
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ALSACE (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ALSACE)
Partenaires : Centre national de la recherche scientifique
Montant : 170000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : Metalloenzymes with transition metal-sulfide complexes located at their active sites play a key role in several metabolic pathways comprising carbon fixation processes as well as redox processes. Because of the simplicity of these metal-sulfide complexes and the diversity of their functions, their prebiotic origin was postulated and it has been envisaged that transition metal sulfides might have played a role as primitive catalysts in the first steps of chemical evolution. In this respect, hydrothermal vents might be considered as ideal sites where these first steps might have occurred. Indeed, the fluids which are emitted in the seawater at these sites contains various transition metal sulfides (e.g. Fe, Ni, Co sulfides) and gases (H2S, CO2, CO, H2, COS, notably) to which a role in prebiotic chemistry has been postulated. This is a very active field, at the moment, as shown by the recent publication of a series of important articles devoted, in this context, to the investigation of the potential of transition metal sulfide chemistry in prebiotic chemistry. Our project is devoted, to the investigation of a central question of prebiotic chemistry, which was underestimated so far, namely the origin of lipids. This is a key issue since compartimentalization is a perequisite for the emergence of cellular life. Therefore, a viable prebiotic pathway to their synthesis would fill an important gap in the first steps of chemical evolution. Indeed, amphiphilic molecules would enable the spontaneous formation of micelles/vesicles able to encapsulate organic molecules and to catalyze various reactions of prebiotic interest based on hydrophobic interactions.  The main objective of our project is to evaluate the potential of the conditions prevailing in the vicinity of hydrothermal vents and of the catalysis by transition metal sulfides for the formation of high molecular weight functionalised lipids (ideally >C10), potential precursors of membrane constituents by means of laboratory simulation experiments. These experiments will involve the constituents of the fluids emitted in the seawater at hydrothermal vents such as H2S, various transition metal sulfides, as well as C1 carbon sources comprising CO2, CO and COS. This project is based on preliminary studies which have been performed very recently at the Laboratoire de Géochimie Bioorganique, and which led to the discovery of a geochemically plausible iterative pathway leading from CO2/CO and H2S to thiols, carboxylic acids, thioacids and thioesters (limited to C4 so far), under aqueous conditions and in the presence of iron and nickel sulfides as catalysts. Several approaches might be envisaged to favour the formation of functionalized amphiphilic lipids. These approaches, which of course must be geochemically relevant, will take into account the main factors influencing the yields of the successive elongation steps in the overall pathway studied so far.  One might envisage, in a first stage, improving and optimizing the transition metal catalysts used. It is clear, in this respect, that the nature of the transition metal sulfides, their mineralogical phases as well as the specific surface available will influence their efficiency. This might be achieved, notably, by dispersing the transition metal sulfides on the surface of other minerals (such as clays for instance) and by extending the set of catalysts used limited, so far, to Fe and Ni sulfides to Co, Cu, Zn, Mn, Co, Pb sulfides, which also occur at the hydrothermal vents.  In a second stage, we envisage to improve the various steps involved in the iterative chain elongation pathway by limiting the reactions leading to dead ends (like carboxylic acids) by various geochemically relevant approaches involving notably, the use of, polyphosphates as additional reagents. This would allow the carboxylic acids to be transformed into related thioacids/thioesters (via acylphosphates) able to enter again the chain elongation process. Experi...