ID   1.21.98.5
DE   tetraether lipid synthase.
AN   GDGT/MA synthase.
CA   (1) 2 AH2 + 2 archaetidylglycerol + 4 S-adenosyl-L-methionine =
CA   4 5'-deoxyadenosine + 2 A + glycerol dibiphytanyl glycerol tetraether
CA   glycerophospholipid + 4 H(+) + 4 L-methionine.
CA   (2) AH2 + archaetidylglycerol + 2 S-adenosyl-L-methionine =
CA   2 5'-deoxyadenosine + A + 2 H(+) + 2 L-methionine + macrocyclic
CA   archaetidylglycerol.
CC   -!- This archaeal enzyme catalyzes a C-C bond formation during the
CC       biosynthesis of tetraether lipids.
CC   -!- The bond is formed between the termini of two lipid tails from two
CC       glycerophospholipids to generate the macrocycle glycerol dibiphytanyl
CC       glycerol tetraether (GDGT).
CC   -!- The enzyme does not distinguish whether the two lipids are connected
CC       in antiparallel or parallel geometry, resulting in formation of two
CC       forms of the product, which are known as caldarchaeol and
CC       isocaldarchaeol, respectively.
CC   -!- The enzyme can also form macrocyclic archaeol phospholipids by
CC       joining the two lipid tails of a single substrate molecule.
CC   -!- Even though the reaction shown here describes phospholipid
CC       substrates, the enzyme can also act on glycolipids or lipids that
CC       contains mixed types of polar head groups.
CC   -!- The enzyme is a radical SAM enzyme that contains 3 [4Fe-4S] clusters
CC       and one mononuclear rubredoxin-like iron ion, each found in a
CC       separate domain.
CC   -!- The enzyme uses the 5'-deoxyadenosyl radical to initiate the
CC       reaction, which involves the formation of an intermediate bond
CC       between the substrate carbon and a sulfur of one of the [4Fe-4S]
CC       clusters.
CC   -!- Two radicals are needed per C-C bond formed. The source of the
CC       required additional electrons is not known.
//