Vib-PT, an Aromatic Prenyltransferase Involved in the Biosynthesis of Vibralactone from Stereum vibrans.

Vibralactone, a hybrid compound derived from phenols and a prenyl group, is a strong pancreatic lipase inhibitor with a rare fused bicyclic ß-lactone skeleton. Recently, a researcher reported a vibralactone derivative (compound C1) that caused inhibition of pancreatic lipase with a half-maximal inhibitory concentration of 14 nM determined by structure-based optimization, suggesting a potential candidate as a new antiobesity treatment. In the present study, we sought to identify the main gene encoding prenyltransferase in Stereum vibrans, which is responsible for the prenylation of phenol leading to vibralactone synthesis. Two RNA silencing transformants of the identified gene (vib-PT) were obtained through Agrobacterium tumefaciens-mediated transformation. Compared to wild-type strains, the transformants showed a decrease in vib-PT expression ranging from 11.0 to 56.0% at 5, 10, and 15 days in reverse transcription-quantitative PCR analysis, along with a reduction in primary vibralactone production of 37 to 64% at 15 and 21 days, respectively, as determined using ultra-high-performance liquid chromatography-mass spectrometry analysis. A soluble and enzymatically active fusion Vib-PT protein was obtained by expressing vib-PT in Escherichia coli, and the enzyme's optimal reaction conditions and catalytic efficiency (Km /kcat) were determined. In vitro experiments established that Vib-PT catalyzed the C-prenylation at C-3 of 4-hydroxy-benzaldehyde and the O-prenylation at the 4-hydroxy of 4-hydroxy-benzenemethanol in the presence of dimethylallyl diphosphate. Moreover, Vib-PT shows promiscuity toward aromatic compounds and prenyl donors.IMPORTANCE Vibralactone is a lead compound with a novel skeleton structure that shows strong inhibitory activity against pancreatic lipase. Vibralactone is not encoded by the genome directly but rather is synthesized from phenol, followed by prenylation and other enzyme reactions. Here, we used an RNA silencing approach to identify and characterize a prenyltransferase in a basidiomycete species that is responsible for the synthesis of vibralactone. The identified gene, vib-PT, was expressed in Escherichia coli to obtain a soluble and enzymatically active fusion Vib-PT protein. In vitro characterization of the enzyme demonstrated the catalytic mechanism of prenylation and broad substrate range for different aromatic acceptors and prenyl donors. These characteristics highlight the possibility of Vib-PT to generate prenylated derivatives of aromatics and other compounds as improved bioactive agents or potential prodrugs.

Biotransformation of saponins by endophytes isolated from Panax notoginseng.

The biotransformation of the major saponins in Panax notoginseng, including the ginsenosides Rg1, Rh1, Rb1, and Re, by endophytes isolated from P. notoginseng was studied. One hundred and thirty-six endophytes were isolated and screened for their biotransformational abilities. The results showed that five of the tested endophytes were able to transform these saponins. These five strains were identified based on their ITS or 16S rDNA sequences, which revealed that they belonged to the genera Fusarium, Nodulisporium, Brevundimonas, and Bacillus genera. Ten transformed products were isolated and identified, including a new compound 6-O-[α-L-rhamnopyranosyl-(1→2)-ß-D-glucopyranosyl]-20-O-ß-D-glucopyranosyldammarane-3,6,12,20,24,25-hexaol (3), and nine known compounds, compound K (1), ginsenoside F2 (2), vinaginsenoside R13 (4), vinaginsenoside R22 (5), pseudo-ginsenoside RT4 (6), (20S)-protopanaxatriol (7), ginsenoside Rg1 (8), vinaginsenoside R15 (9), and (20S)-3-O-ß-D-glucopyranosyl-6-O-ß-D-glucopyranosylprotopanaxatriol (10). This is the first study on the biotransformation of chemical components in P. notoginseng by endophytes isolated from the same plant.

A new sesquiterpene from endophytic fungus Aspergillus sp.

A fungal strain named YLF-14 was isolated from the leaf of Altingia yunnunensis. Based on the sequence at the internal transcribed spacer (ITS) region, the strain was identified as an Aspergillus sp.. A new sesquiterpene 5ß,8aß-dimethyl-3,4,4aß,5,6,7,8,8a-octahydronaphthalene-1,2,5α-trimethanol (1) and a known compound 12-N-methylcyclo-(L-tryptophyl-L-phenylalanyl) (2) were isolated from the culture of this strain. Bioassay experiments showed that the two compounds had no obvious effect on the growth of tested bacteria and nematodes.