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  • New insights into the biosynthesis of prenylated xanthones: Xptb from Aspergillus nidulans catalyses an O-prenylation of xanthones.

New insights into the biosynthesis of prenylated xanthones: Xptb from Aspergillus nidulans catalyses an O-prenylation of xanthones.

Chembiochem : a European journal of chemical biology (2012-11-15)
Daniel Pockrandt, Lena Ludwig, Aili Fan, Gabriele M König, Shu-Ming Li
ABSTRACT

Gene-inactivation experiments have indicated that the putative prenyltransferase XptB from Aspergillus nidulans was likely to be responsible for the prenylation of 1,7-dihydroxy-6-methyl-8-hydroxymethylxanthone. Recently, it was suggested that this enzyme might also accept as substrate the benzophenone arugosin H, which is assumed to be a precursor of prenylated xanthones. In this study, five benzophenones and ten xanthones were incubated with purified recombinant XptB in the presence of dimethylallyl diphosphate (DMAPP). XptB accepted four xanthones as substrates, including the proposed natural substrate, and catalysed regiospecific O-prenylations at C-7 of the xanthone core. K(m) values in the range of 0.081-1.1 mM and turnover numbers (k(cat)) between 0.02 and 0.5 s(-1) were determined for the accepted xanthones. The kinetic parameters for DMAPP were found to be 0.024 mM (K(m)) and 0.13 s(-1) (k(cat)). Arugosin H was not accepted by XptB under the tested conditions. XptB was relatively specific towards its prenyl donor and did not accept geranyl or farnesyl diphosphate as substrate. Mn(2+) and Co(2+) strongly enhanced XptB activity (up to eightfold); this has not been reported before for prenyltransferases of the DMATS superfamily.

MATERIALS
Product Number
Brand
Product Description

Supelco
Melting point standard 47-49°C, analytical standard
Supelco
Mettler-Toledo Calibration substance ME 18870, Benzophenone, traceable to primary standards (LGC)
Sigma-Aldrich
Benzophenone, purified by sublimation, ≥99%
Supelco
Benzophenone, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
Benzophenone, analytical standard
Sigma-Aldrich
Benzophenone, ReagentPlus®, 99%
Benzophenone, European Pharmacopoeia (EP) Reference Standard