Function
Geranylgeranyl pyrophosphate synthase; part of the gene cluster that mediates the biosynthesis of lolitrems, indole-diterpene mycotoxins that are potent tremorgens in mammals, and are synthesized by clavicipitaceous fungal endophytes in association with their grass hosts (PubMed:16765617). The geranylgeranyl diphosphate (GGPP) synthase ltmG is proposed to catalyze the first step in lolitrem biosynthesis (PubMed:16765617, PubMed:15991026). LtmG catalyzes a series of iterative condensations of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP), geranyl diphosphate (GPP), and farnesyl diphosphate (FPP), to form GGPP (PubMed:16765617, PubMed:15991026). GGPP then condenses with indole-3-glycerol phosphate to form 3-geranylgeranylindole, an acyclic intermediate, to be incorporated into paxilline (PubMed:16765617). Either ltmG or ltmC could be responsible for this step, as both are putative prenyl transferases (PubMed:16765617). The FAD-dependent monooxygenase ltmM then catalyzes the epoxidation of the two terminal alkenes of the geranylgeranyl moiety, which is subsequently cyclized by ltmC, to paspaline (PubMed:16765617, PubMed:15991026). The cytochrome P450 monooxygenases ltmQ and ltmP can sequentially oxidize paspaline to terpendole E and terpendole F (PubMed:22750140). Alternatively, ltmP converts paspaline to an intermediate which is oxidized by ltmQ to terpendole F (PubMed:22750140). LtmF, ltmK, ltmE and ltmJ appear to be unique to the epichloe endophytes (PubMed:16765617, PubMed:15991026). The prenyltransferase ltmF is involved in the 27-hydroxyl-O-prenylation (PubMed:22750140). The cytochrome P450 monooxygenase ltmK is required for the oxidative acetal ring formation (PubMed:22750140). The multi-functional prenyltransferase ltmE is required for C20- and C21-prenylations of the indole ring of paspalanes and acts together with the cytochrome P450 monooxygenase ltmJ to yield lolitremanes by multiple oxidations and ring closures (PubMed:22750140). The stereoisomer pairs of lolitriol and lolitrem N or lolitrem B and lolitrem F may be attributed to variations in the way in which ring closure can occur under the action of ltmJ (PubMed:22750140). While the major product of this pathway is lolitrem B, the prenyl transferases and cytochrome P450 monooxygenases identified in this pathway have a remarkable versatility in their regio- and stereo-specificities to generate a diverse range of metabolites that are products of a metabolic grid rather than a linear pathway (PubMed:22750140).
Sequence
MTMAANDFPFQCQEKKSYSQPSLVYCNGNIAETYLEEKVLTAPLDYLRALPSKDIRSGLTDAINEFLRVPEEKVLVIKRIIDLLHNASLLIDDIQDSSKLRRGVPVAHHIFGIAQTINSANLAYFIAQRELEKLTNPRAFAIYNEELINLHRGQGMELHWRESLHCPTEDEYLRMIQKKTGGLFRLAIRLLQGESASDDDYVSLIDTLGTLFQIRDDYQNLQSDIYSKNKGYCEDLTEGKFSYPVIHSIRSRPGDVRLINILKQRSEDVMVKQYAVQHIESTGSFAFCQNKIQSLVEQAREQLAALENSSSCGGPVRDILDKLAIKPRANIEVE