The first prenylation step in hyperforin biosynthesis

Abstract

Prenylation reactions contribute considerably to the diversity of natural products. Polyprenylated secondary metabolites include hyperforin which is both quantitatively and pharmacologically a major constituent of the medicinal plant Hypericum perforatum (St. John’s wort). Cell cultures of the related species Hypericum calycinum were found to contain a prenyltransferase activity which is likely to catalyze the first prenylation step in hyperforin biosynthesis. The enzyme was soluble and dependent on a divalent cation, with Fe 2+ leading to maximum activity ( K m = 3.8 mM). The preferred prenyl donor was DMAPP ( K m = 0.46 mM) and the preferred prenyl acceptor was phlorisobutyrophenone ( K m = 0.52 mM). A broad pH optimum from 6.5 to 8.5 and a temperature optimum from 35 to 40 °C were observed. The formation of hyperforins in H. calycinum cell cultures was preceded by an increase in dimethylallyltransferase activity, with the maximum specific activity being 3.6 μkat/kg protein.