HlPT-1, a membrane-bound prenyltransferase responsible for the biosynthesis of bitter acids in hops

[摘要]：Female flowers of hop (Humulus lupulus L) develop a large number of glandular trichomes called lupulin glands that contain a variety of prenylated compounds such as alpha- and beta-acid (humulone and lupulone, respectively), as well as xanthohumol, a chalcone derivative. These prenylated compounds are biosynthe-sized by prenyltransferases catalyzing the transfer of dimethylallyl moiety to aromatic substances. In our previous work, we found HlFT-1 a candidate gene for such a prenyltransferase in a cDNA library constructed from lupulin-enriched flower tissues. In this study, we have characterized the enzymatic properties of HlPT-1 using a recombinant protein expressed in baculovirus-infected insect cells. HlPT-1 catalyzed the first transfer of dimethylallyl moiety to phloroglucinol derivatives, phlorisovalerophenone, phlorisobutyrophenone and phlormethylbutanophenone, leading to the formation of humulone and lupulone derivatives. HlPT-1 also recognized naringenin chalcone as a flavonoid substrate to yield xanthohumol, and this broad substrate specificity is a unique character of HlPT-1 that is not seen in other reported flavonoid prenyltransferases, all of which show strict specificity for their aromatic substrates. Moreover, unlike other aromatic substrate prenyltransferases, HlPT-1 revealed an exclusive requirement for Mg2+ as a divalent cation for its enzymatic activity and also showed exceptionally narrow optimum pH at around pH 7.0. (C) 2011 Elsevier Inc. All rights reserved.

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