Did Archaeal and Bacterial Cells Arise Independently from Noncellular Precursors? A Hypothesis Stating That the Advent of Membrane Phospholipid with Enantiomeric Glycerophosphate Backbones Caused the Separation of the Two Lines of Descent |
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Authors: | Y Koga T Kyuragi M Nishihara N Sone |
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Institution: | (1) Department of Chemistry, University of Occupational and Environmental Health, Yahatanishi-Ku, Kitakyushu 807, Japan, JP;(2) Department of Biochemical Engineering and Science, Faculty of Computer Science and System Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka 820, Japan, JP |
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Abstract: | One of the most remarkable biochemical differences between the members of two domains Archaea and Bacteria is the stereochemistry
of the glycerophosphate backbone of phospholipids, which are exclusively opposite. The enzyme responsible to the formation
of Archaea-specific glycerophosphate was found to be NAD(P)-linked sn-glycerol-1-phosphate (G-1-P) dehydrogenase and it was first purified from Methanobacterium thermoautotrophicum cells and its gene was cloned. This structure gene named egsA (enantiomeric glycerophosphate synthase) consisted of 1,041 bp and coded the enzyme with 347 amino acid residues. The amino
acid sequence deduced from the base sequence of the cloned gene (egsA) did not share any sequence similarity except for NAD-binding region with that of NAD(P)-linked sn-glycerol-3-phosphate (G-3-P) dehydrogenase of Escherichia coli which catalyzes the formation of G-3-P backbone of bacterial phospholipids, while the deduced protein sequence of the enzyme
revealed some similarity with bacterial glycerol dehydrogenases. Because G-1-P dehydrogenase and G-3-P dehydrogenase would
originate from different ancestor enzymes and it would be almost impossible to interchange stereospecificity of the enzymes,
it seems likely that the stereostructure of membrane phospholipids of a cell must be maintained from the time of birth of
the first cell. We propose here the hypothesis that Archaea and Bacteria were differentiated by the occurrence of cells enclosed
by membranes of phospholipids with G-1-P and G-3-P as a backbone, respectively.
Received: 24 March 1997 / Accepted: 21 May 1997 |
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Keywords: | :sn-Glycerol-1-phosphate dehydrogenase — sn-Glycerol-3-phosphate dehydrogenase — Archaea — Bacteria — Ether-linked lipid — Differentiation — Cloning — Primary structure — egsA |
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