Biosynthesis of bicyclic polyprenylated phlorbenzophenones in Hypericum sampsonii

• Applicant: Dr. Benye Liu
• Subject Area: Plant Biochemistry and Biophysics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532485639

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are plant natural products with challenging chemical structures and intriguing biological activities. Their biosynthesis is poorly understood. The acylphloroglucinol core of PPAPs undergoes consecutive prenylation reactions. The attached side chains are believed to cyclize intramolecularly to yield bicyclic polyprenylated acylphloroglucinols (BPAPs) and caged PPAPs. BPAPs and PPAPs can be further subclassified into type A and type B compounds depending on the relative position of the acyl group. A plant that is rich in complex PPAPs is Hypericum sampsonii, a Chinese medicinal plant. Its PPAPs commonly contain the benzoyl residue as acyl group, i.e. they are phlorbenzophenone derivatives. H. sampsonii plants contain nemorosone (type A BPAP) and 7-epi-clusianone (type B BPAP) as major constituents. The attachment of prenyl groups to the phlorbenzophenone core is catalyzed by aromatic prenyltransferase (aPT) enzymes. Comparative transcriptome analysis afforded 32 aPT candidates. Preliminary functional screening disclosed two aPTs (HsPT11 and HsPT18) that catalyze the formation of 7-epi-clusianone (type B BPAP) and nemorosone (type A BPAP), respectively, using the same substrates, namely DMAPP and grandone, a triprenylated phlorbenzophenone. These finding indicated that the biosyntheses of both type of BPAPs are catalyzed by multifunctional aPTs which perform both the intramolecular cyclization of the triprenylated phlorbenzophenone substrate and the addition of a prenyl residue. The objectives of the present proposal include (i) identification of the three upstream aPTs that catalyze the formation grandone, (ii) functional characterization of the cloned aPTs, and (iii) detection of amino acids that determine the regiospecificities of the two multifunctional aPTs by homology modeling, substrate/product docking and site-directed mutagenesis.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Ludger Beerhues