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Racemic Phospholipids for Origin of Life Studies
Open AccessHypothesis

Symmetry Breaking of Phospholipids

Institut de Chimie et de Biochimie Moléculaires et Supramoléculaires (UMR 5246), Université Claude Bernard Lyon 1, Université de Lyon, Bât. Edgar Lederer, 1 rue Victor Grignard, CEDEX, F-69622 Villeurbanne, France
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Author to whom correspondence should be addressed.
In memory of Océane.
Symmetry 2020, 12(9), 1488; https://doi.org/10.3390/sym12091488
Received: 23 July 2020 / Revised: 4 September 2020 / Accepted: 8 September 2020 / Published: 10 September 2020
(This article belongs to the Special Issue Chirality and the Origin of Life)
Either stereo reactants or stereo catalysis from achiral or chiral molecules are a prerequisite to obtain pure enantiomeric lipid derivatives. We reviewed a few plausibly organic syntheses of phospholipids under prebiotic conditions with special attention paid to the starting materials as pro-chiral dihydroxyacetone and dihydroxyacetone phosphate (DHAP), which are the key molecules to break symmetry in phospholipids. The advantages of homochiral membranes compared to those of heterochiral membranes were analysed in terms of specific recognition, optimal functions of enzymes, membrane fluidity and topological packing. All biological membranes contain enantiomerically pure lipids in modern bacteria, eukarya and archaea. The contemporary archaea, comprising of methanogens, halobacteria and thermoacidophiles, are living under extreme conditions reminiscent of primitive environment and may indicate the origin of one ancient evolution path of lipid biosynthesis. The analysis of the known lipid metabolism reveals that all modern cells including archaea synthetize enantiomerically pure lipid precursors from prochiral DHAP. Sn-glycerol-1-phosphate dehydrogenase (G1PDH), usually found in archaea, catalyses the formation of sn-glycerol-1-phosphate (G1P), while sn-glycerol-3-phosphate dehydrogenase (G3PDH) catalyses the formation of sn-glycerol-3-phosphate (G3P) in bacteria and eukarya. The selective enzymatic activity seems to be the main strategy that evolution retained to obtain enantiomerically pure lipids. The occurrence of two genes encoding for G1PDH and G3PDH served to build up an evolutionary tree being the basis of our hypothesis article focusing on the evolution of these two genes. Gene encoding for G3PDH in eukarya may originate from G3PDH gene found in rare archaea indicating that archaea appeared earlier in the evolutionary tree than eukarya. Archaea and bacteria evolved probably separately, due to their distinct respective genes coding for G1PDH and G3PDH. We propose that prochiral DHAP is an essential molecule since it provides a convergent link between G1DPH and G3PDH. The synthesis of enantiopure phospholipids from DHAP appeared probably firstly in the presence of chemical catalysts, before being catalysed by enzymes which were the products of later Darwinian selection. The enzymes were probably selected for their efficient catalytic activities during evolution from large libraries of vesicles containing amino acids, carbohydrates, nucleic acids, lipids, and meteorite components that induced symmetry imbalance. View Full-Text
Keywords: symmetry breaking; dihydroxyacetone phosphate; sn-glycerol-1-phosphate dehydrogenase; sn-glycerol-3-phosphate dehydrogenase; membrane evolution symmetry breaking; dihydroxyacetone phosphate; sn-glycerol-1-phosphate dehydrogenase; sn-glycerol-3-phosphate dehydrogenase; membrane evolution
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Fiore, M.; Buchet, R. Symmetry Breaking of Phospholipids. Symmetry 2020, 12, 1488.

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