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

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.

Phylogeny determined by protein domain content

“…In recent years, the question has been raised as to whether there is a genuine tree of life with a common ancestral organism at its root (36)(37)(38)(39). Instead, challengers propose that the three superkingdoms arose independently from a community of primitive and undifferentiated cells that were freely exchanging their genetic components.…”

CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate Cytidyltransferase in the Methanogenic ArchaeonMethanothermobacter thermoautotrophicus

“…The GP backbone of phospholipid in Archaea is sn-glycero-1-phosphate (G-1-P), which is the enantiomer of its bacterial and eucaryal counterparts (1). So far, no exception to this arrangement in the stereostructure of GP has been found, and remains the most fundamental distinguishing characteristic of the organisms in each of these domains (2). In vitro studies of polar lipid biosynthesis in Archaea have been carried out since 1990, and the enzymes catalyzing the first three steps have been identified (Refs.…”

Biosynthetic Mechanism forL-Gulose in Main Polar Lipids ofThermoplasma acidophilumand Possible Resemblance to Plant Ascorbic Acid Biosynthesis

“…GC-MS data were recorded with a QP-5000 spectrometer (Shimadzu Corp., Kyoto, Japan preparation of (6S) and (6R)- [4-2 H,6-3 H]-2 by Yu et al 40,41) and is subsequently described as a series of preparative steps (Scheme 1). (12). A solution of 11 (6.31 g, 24.1 mmol) dissolved in anhydrous pyridine (145 mL) was added to p-toluenesulfonyl chloride (11.0 g, 57.7 mmol) and N,N-dimethylaminopyridine (DMAP, 0.46 g, 3.77 mmol).…”

“…10) However, several features of thermophilic archaea have led to them being positioned at an important stage for imagining the origin of life on Earth. 11,12) Among these features, the Thermoplasmata class lacks cell walls and has plasma membranes directly in contact with the high pH exterior. 13,14) The relationship between the tolerance of Thermoplasmata for harsh conditions and its lipids has attracted great attention from microbiologists and material scientists.…”