Characterization of the precursor of tetraether lipid biosynthesis in the thermoacidophilic archaeon Thermoplasma acidophilum

Polar lipid biosynthesis in the thermoacidophilic archaeon Thermoplasma acidophilum was analyzed using terbinafine, an inhibitor of tetraether lipid biosynthesis. Cells of T. acidophilum were labeled with [(14)C]mevalonic acid, and their lipids were extracted and analyzed by two-dimensional thin-layer chromatography. Lipids labeled with [(14)C]mevalonic acid, [(14)C]glycerol, and [(32)P]orthophosphoric acid were extracted and hydrolyzed under different conditions to determine the structure of polar lipids. The polar lipids were estimated to be archaetidylglycerol, glycerophosphatidylcaldarchaetidylglycerol, caldarchaetidylglycerol, and beta- l-gulopyranosylcaldarchaetidylglycerol, the main polar lipid of T. acidophilum. Pulse and chase experiments with terbinafine revealed that one tetraether lipid molecule is synthesized by head-to-head condensation of two molecules of archaetidylglycerol and that a sugar group of tetraether phosphoglycolipid is expected to attach to the tetraether lipid core after head-to-head condensation in T. acidophilum. A precursor accumulated in the presence of terbinafine with a fast-atom-bombardment mass spectrometry peak m/z 806 was compatible with archaetidylglycerol. The relative height of the peak m/z 806 decreased after removal of the inhibitor. The results suggest that most of the precursor, archaetidylglycerol, is in fully saturated form.

Characterization of caldarchaetidylglycerol analogs, dialkyl-type and trialkyl-type, from Thermoplasma acidophilum

The structures of three kinds of phospholipids (PL-X, PL-Y, and PL-T) isolated from Thermoplasma acidophilum have been characterized. The core lipid of PL-Y was caldarchaeol, and that of PL-X was archaeol. The composition of the hydrocarbon chains of the PL-T core lipid was C20 phytane and C40 isoprenoid in a molar ratio of 2 to 1. The major molecular species of the C40 isoprenoid was acyclic without the cyclopentane ring. These three kinds of intact phospholipids commonly had glycerophosphate residues as polar head groups. The structure of PL-T was characterized as trialkyl-type caldarchaetidylglycerol, PL-Y as caldarchaetidylglycerol, and PL-X as archaetidylglycerol.