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Crystal structure of elongation domain of Phomopsis amygdali fusicoccadiene synthase complexed with cobalt ions and pamidronate
Structural highlights
FunctionFC1_PHOAM Multifunctional diterpene synthase; part of the 2 gene clusters that mediate the biosynthesis of fusicoccins, diterpene glucosides that display phytohormone-like activity and function as potent activators of plasma membrane H(+)-ATPases in plants by modifying 14-3-3 proteins and cause the plant disease constriction canker (PubMed:17360612, PubMed:26734760). The first step in the pathway is performed by the fusicoccadiene synthase PaFS that possesses both prenyl transferase and terpene cyclase activity, converting isopentenyl diphosphate and dimethylallyl diphosphate into geranylgeranyl diphosphate (GGDP) and successively converting GGDP into fusicocca-2,10(14)-diene, a precursor for fusicoccin H (PubMed:17360612, PubMed:26734760). Fusicoccadiene synthase is an allosteric enzyme for GGPP cyclization that generates 64% fusicoccadiene, 9% delta-araneosene, and one additional unidentified diterpene product, when incubated with GGPP (PubMed:26734760). In the absence of isopentenyl diphosphate (IPP), PaFS can also solvolyze the shorter chain geranyl diphosphate (GPP) and farnesyl diphosphate (FPP) as alternative substrates to yield predominantly acyclic products. FPP is converted to farnesol (60.5%), nerolidol (14.0%), and farnesene (14.0%), while GPP is converted to a mixture of geraniol (59.5%) and linalool (35.0%) (PubMed:26734760). The second step is the oxidation at the C-8 position by the cytochrome P450 monooxygenase PaP450-2 to yield fusicocca-2,10(14)-diene-8-beta-ol (PubMed:22870285). The cytochrome P450 monooxygenase PaP450-1 then catalyzes the hydroxylation at the C-16 position to produce fusicocca-2,10(14)-diene-8-beta,16-diol (PubMed:22870285). The dioxygenase fc-dox then catalyzes the 16-oxydation of fusicocca-2,10(14)-diene-8-beta,16-diol to yield an aldehyde (8-beta-hydroxyfusicocca-1,10(14)-dien-16-al) (PubMed:21299202, PubMed:22870285). The short-chain dehydrogenase/reductase fc-sdr catalyzes the reduction of the aldehyde to yield fusicocca-1,10(14)-diene-8-beta,16-diol (PubMed:21299202, PubMed:22870285). The next step is the hydroxylation at C-9 performed by the cytochrome P450 monooxagenase PaP450-3 that leads to fusicoccin H aglycon which is glycosylated to fusicoccin H by the O-glycosyltransferase PAGT (PubMed:22870285). Hydroxylation at C-12 by the cytochrome P450 monooxygenase PaP450-4 leads then to the production of fusicoccin Q and is followed by methylation by the O-methyltransferase PAMT to yield fusicoccin P (PubMed:22870285). Fusicoccin P is further converted to fusicoccin J via prenylation by the O-glucose prenyltransferase PaPT (PubMed:22287087). Cytochrome P450 monooxygenase PaP450-5 then performs hydroxylation at C-19 to yield dideacetyl-fusicoccin A which is acetylated to 3'-O-deacetyl-fusicoccin A by the O-acetyltransferase PaAT-2 (PubMed:22870285). Finally, a another acetylation by the O-acetyltransferase PaAT-1 yields fusicoccin A (PubMed:22870285).[1] [2] [3] [4] [5] Publication Abstract from PubMedFusicoccin A is a diterpene glucoside phytotoxin generated by the fungal pathogen Phomopsis amygdali that causes the plant disease constriction canker, first discovered in New Jersey peach orchards in the 1930s. Fusicoccin A is also an emerging new lead in cancer chemotherapy. The hydrocarbon precursor of fusicoccin A is the tricyclic diterpene fusicoccadiene, which is generated by a bifunctional terpenoid synthase. Here, we report X-ray crystal structures of the individual catalytic domains of fusicoccadiene synthase: the C-terminal domain is a chain elongation enzyme that generates geranylgeranyl diphosphate, and the N-terminal domain catalyzes the cyclization of geranylgeranyl diphosphate to form fusicoccadiene. Crystal structures of each domain complexed with bisphosphonate substrate analogues suggest that three metal ions and three positively charged amino acid side chains trigger substrate ionization in each active site. While in vitro incubations reveal that the cyclase domain can utilize farnesyl diphosphate and geranyl diphosphate as surrogate substrates, these shorter isoprenoid diphosphates are mainly converted into acyclic alcohol or hydrocarbon products. Gel filtration chromatography and analytical ultracentrifugation experiments indicate that full-length fusicoccadiene synthase adopts hexameric quaternary structure, and small-angle X-ray scattering data yield a well-defined molecular envelope illustrating a plausible model for hexamer assembly. Structure and Function of Fusicoccadiene Synthase, a Hexameric Bifunctional Diterpene Synthase.,Chen M, Chou WK, Toyomasu T, Cane DE, Christianson DW ACS Chem Biol. 2016 Jan 6. PMID:26734760[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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