BIOSYNTHESIS OF ARCHAEBACTERIAL ETHER LIPIDS - FORMATION OF ETHER LINKAGES BY PRENYLTRANSFERASES

Biosynthesis of (R)-2,3-di-O-phytanylglycerol (1), the core lipid of the membranes in the strict anaerobe Methanobacterium thermoautotrophicum, was studied in cell-free preparations. Two prenyltransferase activities were separated by ultracentrifugation. The cytosolic fraction contained activity for (S)-3-O-geranylgeranylglyceryl phosphate synthase (GGGP synthase), which catalyzes alkylation of (S)-glyceryl phosphate [(S)-3-OP] by geranylgeranyl diphosphate (5-OPP), while the pellet contained activity for (S)-2,3-O-digeranylgeranylglyceryl phosphate synthase (DGGGP synthase), which catalyzes alkylation of (S)-3-O-geranylgeranylglyceryl phosphate [(S)-12-OP] by 5-OPP. (S)-3-OP and 5-OPP were strongly preferred among the various compounds tested as prenyl acceptors [(S)-3-OP, (R)-3-OP, glycerol (3-OH), and dihydroxyacetone phosphate (4-OP)] and as prenyl donors [5-OPP, phytyl diphosphate (6-OPP), phytanyl diphosphate (7-OPP), farnesyl diphosphate (10-OPP), and farnesylgeranyl diphosphate (11-OPP)]. The products from the enzymatic reactions catalyzed by GGGP synthase and DGGGP synthase were characterized by hydrolysis of the phosphate moieties with alkaline phosphatase and comparisons of the glyceryl ethers with synthetic samples. These results demonstrate that the ether linkages in the core lipids of archaebacteria are formed in two distinct steps by a cytosolic GGGP synthase and a membrane-associated DGGGP synthase.