Pentaketide chromone synthase

Aloe (Aloe arborescens) is a medicinal plant rich in aromatic polyketides such as pharmaceutically important aloenin (a hexaketide pyrone), aloesin (a heptaketide chromone), and barbaloin (an octaketide anthrone) (Fig. 4a). Pentaketide chromone synthase (PCS) and octaketide synthase (OKS) are novel plant-specific type III PKSs, which were obtained from the aloe plant by RT-PCR cloning using degenerate oligonucleotide primers based on the conserved sequences of known CHS enzymes [30-33]. The deduced amino acid sequences of PCS and OKS are 91% identical (368/403), and show 50-60% identity to those of other CHS superfamily type III PKSs of plant origin OKS shares 60% identity (240/403) with CHS from... 

Morita H, Kondo S, Oguro S, Noguchi H, Sugio S, Abe I, Kohno T (2007) Structural insight into chain-length control and product specificity of pentaketide chromone synthase from Aloe arborescens. Chem Biol 14 359-369... 

FIGURE 3. (A) Crystal structure of pentaketide chromone synthase with a bound CoA in the active site (2D3M, Plate II). (B) The active site showing part of the bound CoA and the three catalytically significant side chains. The Cys side chain is oxidized to —S02 in the crystal structure (Plate III). The reduced —SH group of Cysl77 is needed for catalysis... 

Chalcone synthase (CHS), the first plant natural product polyketide synthase (PKS) to be characterized at the molecular level (39), catalyzes the condensation of 4-coumaroyl-CoA with three molecules of malonyl-CoA to afford naringenin chalcone, a precursor of the major classes of plant flavonoids. The cloning of a novel type III pentaketide chromone synthase (PCS) from aloe (Aloe arborescens, Liliaceae) rich in aromatic polyketides, especially quinones such as aloe-emodin and emodin, resulted in... 

Abe I, Utsumi Y, Oguro S, Morita H, Sano Y, Noguchi H (2005) A plant Type III polyketide synthase that produces pentaketide chromone. J Am Chem Soc 127 1362-1363... 

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