Quantitative structure-activity relationship for estrogenic flavonoids from Psoralea corylifolia.

A combination of in vitro and in silico approaches was employed to investigate the estrogenic activities of flavonoid compounds from Psoralea corylifolia. In order to develop fluorescence polarization (FP) assay for flavonoids, a soluble recombinant protein human estrogen receptor α ligand binding domain (hERα-LBD) was produced in Escherichia coli strain. The competition binding experiment was performed by using coumestrol (CS) as a tracer. The result of FP assay suggested that the tested flavonoids can bind to hERα-LBD as affinity ligands, except for corylin. Then, molecular modeling was conducted to explore the binding modes between hERα-LBD and flavonoids. All the tested compounds fit into the hydrophobic binding pocket of hERα-LBD. The hydrophobic and hydrogen-bonding interactions are dominant forces to stabilize the flavonoids-hERα-LBD binding. It can be speculated from molecular docking study that the hydroxyl groups and prenyl group are essential for flavonoid compounds to possess estrogenic activities. Both methylation of hydroxyl group and cyclization of prenyl group significantly diminish the estrogenic potency of flavonoids. Furthermore, quantitative structure-activity relationship (QSAR) analysis was performed by the calculated binding energies of flavonoids coupled with their determined binding affinities. Comparison between the docking scores and the pIC50 values yields an R-squared value of 0.9722, indicating that the estrogenic potency of flavonoids is structure-dependent. In conclusion, molecular docking can potentially be applied for predicting the receptor-binding properties of undescribed compounds based on their molecular structure.

Comparative transcriptome analysis of tobacco (Nicotiana tabacum) leaves to identify aroma compound-related genes expressed in different cultivated regions.

To identify genes that are differentially expressed in tobacco in response to environmental changes and to decipher the mechanisms by which aromatic carotenoids are formed in tobacco, an Agilent Tobacco Gene Expression microarray was adapted for transcriptome comparison of tobacco leaves derived from three cultivated regions of China, Kaiyang (KY), Weining (WN) and Tianzhu (TZ). A total of 1,005 genes were differentially expressed between leaves derived from KY and TZ, 733 between KY and WN, and 517 between TZ and WN. Genes that were upregulated in leaves from WN and TZ tended to be involved in secondary metabolism pathways, and included several carotenoid pathway genes, e.g., NtPYS, NtPDS, and NtLCYE, whereas those that were down-regulated tended to be involved in the response to temperature and light. The expression of 10 differentially expressed genes (DEGs) was evaluated by real-time quantitative polymerase chain reaction (qRT-PCR) and found to be consistent with the microarray data. Gene Ontology and MapMan analyses indicate that the genes that were differentially expressed among the three cultivated regions were associated with the light reaction of photosystem II, response to stimuli, and secondary metabolism. High-performance liquid chromatography (HPLC) analysis showed that leaves derived from KY had the lowest levels of lutein, ß-carotene, and neoxanthin, whereas the total carotenoid content in leaves from TZ was greatest, a finding that could well be explained by the expression patterns of DEGs in the carotenoid pathway. These results may help elucidate the molecular mechanisms underlying environmental adaptation and accumulation of aroma compounds in tobacco.