2 research outputs found
Structure and Function of Fusicoccadiene Synthase, a Hexameric Bifunctional Diterpene Synthase
Fusicoccin
A is a diterpene glucoside phytotoxin generated by the
fungal pathogen <i>Phomopsis amygdali</i> 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 <i>in vitro</i> 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