AUTHOR=Abe Ikuro 

TITLE=Benzalacetone Synthase

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 3 - 2012

YEAR=2012

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2012.00057

DOI=10.3389/fpls.2012.00057

ISSN=1664-462X

ABSTRACT=<p>Benzalacetone synthase, from the medicinal plant <italic>Rheum palmatum</italic> (<italic>Rp</italic>BAS), is a plant-specific chalcone synthase (CHS) superfamily of type III polyketide synthase (PKS). <italic>Rp</italic>BAS catalyzes the one-step, decarboxylative condensation of 4-coumaroyl-CoA with malonyl-CoA to produce the C<sub>6</sub>–C<sub>4</sub> benzalacetone scaffold. The X-ray crystal structures of <italic>Rp</italic>BAS confirmed that the diketide-forming activity is attributable to the characteristic substitution of the conserved active-site “gatekeeper” Phe with Leu. Furthermore, the crystal structures suggested that <italic>Rp</italic>BAS employs novel catalytic machinery for the thioester bond cleavage of the enzyme-bound diketide intermediate and the final decarboxylation reaction to produce benzalacetone. Finally, by exploiting the remarkable substrate tolerance and catalytic versatility of <italic>Rp</italic>BAS, precursor-directed biosynthesis efficiently generated chemically and structurally divergent, unnatural novel polyketide scaffolds. These findings provided a structural basis for the functional diversity of the type III PKS enzymes.</p>