The reviewed HAMAP record identifies Q88E69 as the two-cluster radical-SAM GTP 3',8'-cyclase EC 4.1.99.22.
"CC -!- FUNCTION: Catalyzes the cyclization of GTP to (8S)-3',8-cyclo-7,8-
CC dihydroguanosine 5'-triphosphate. {ECO:0000255|HAMAP-Rule:MF_01225}.
CC -!- CATALYTIC ACTIVITY:
CC Reaction=GTP + AH2 + S-adenosyl-L-methionine = (8S)-3',8-cyclo-7,8-
CC dihydroguanosine 5'-triphosphate + 5'-deoxyadenosine + L-methionine +
CC A + H(+); Xref=Rhea:RHEA:49576, ChEBI:CHEBI:13193, ChEBI:CHEBI:15378,
CC ChEBI:CHEBI:17319, ChEBI:CHEBI:17499, ChEBI:CHEBI:37565,
CC ChEBI:CHEBI:57844, ChEBI:CHEBI:59789, ChEBI:CHEBI:131766;
CC EC=4.1.99.22; Evidence={ECO:0000255|HAMAP-Rule:MF_01225};
CC -!- COFACTOR:
CC Name=[4Fe-4S] cluster; Xref=ChEBI:CHEBI:49883;
CC Evidence={ECO:0000255|HAMAP-Rule:MF_01225};
CC Note=Binds 2 [4Fe-4S] clusters. Binds 1 [4Fe-4S] cluster coordinated
CC with 3 cysteines and an exchangeable S-adenosyl-L-methionine and 1
CC [4Fe-4S] cluster coordinated with 3 cysteines and the GTP-derived
CC substrate. {ECO:0000255|HAMAP-Rule:MF_01225};"