Birth of Archaeal Cells: Molecular Phylogenetic Analyses of G1P Dehydrogenase, G3P Dehydrogenases, and Glycerol Kinase Suggest Derived Features of Archaeal Membranes Having G1P Polar Lipids

Figure 2

Five hypotheses regarding the early evolution of cell membrane glycerolipid backbone. LUCA: last universal common ancestor. C. commonote was defined as the cellular last universal common ancestor [5]. (a) The C. commonote had a heterochiral polar lipid membrane. Both G1P and G3P were used, but they might have been synthesized via a nonenzymatic pathway (absence of G1PDH and G3PDH in C. commonote cell) or via an enzymatic pathway (certain enzymes did not have specificity to either G1P or G3P; both G1P and G3P were created by a single enzyme). Then, C. bacteria acquired G3PDH and acquired a G3P-homochiral polar lipid membrane. On the other hand, the archaeal common ancestor acquired G1PDH with a G1P-homochiral polar lipid membrane. (b) The C. commonote had G3PDH. Therefore, C. commonote had a G3P-homochiral polar lipid membrane. C. archaea acquired G1PDH, and then the G3P-homochiral polar lipid membrane was replaced by a G1P-homochiral polar lipid membrane. (c) C. commonote had G1PDH. Therefore, C. commonote had a G1P-homochiral polar lipid membrane. C. bacteria acquired G3PDH, and then the G1P-homochiral polar lipid membrane was replaced by a G3P-homochiral polar lipid membrane. (d) C. commonote had both G1PDH and G3PDH. Therefore, C. commonote had a heterochiral polar lipid membrane (G1PDH created G1P and G3PDH created G3P). In the bacterial line, G1PDH was lost. Then, Bacteria acquired a G3P-homochiral polar lipid membrane. G3PDH was then lost in the archaeal line. Archaea then acquired a G1P-homochiral polar lipid membrane. (e) The LUCA did not have membrane structure. (The C. commonote is cellular LUCA. Therefore, we do not use the term “C. commonote” for this hypothesis.) The bacterial line then acquired G3PDH and acquired a G3P-homochiral polar lipid membrane. The archaeal line also acquired G1PDH and acquired a G1P-homochiral polar lipid membrane.

(a)

(b)

(c)

(d)

(e)