The high throughput screening of neuropeptide FF2 receptor ligands from Korean herbal plant extracts.

We have screened 356 libraries of Korean herbal plant extracts to find potential anti-obesity drugs. We employed the recently developed fluorescence polarization high throughput screening (FP HTS) assays of human neuropeptide FF (NPFF) receptors in 384-well microtiter plates. The primary hits were cherry-picked from the libraries and further analyzed by secondary displacement curve assays, in vitro GTPgammaS binding assays and cell-based CRE luciferase reporter assays. Agonists of NPFF receptors showed biphasic affinity curves while the antagonist, BIBP 3226, gave a monophasic affinity curve in competitive binding assays. We isolated and characterized two agonists of human NPFF2 receptor, PC 314 with K(i) of 1.42 microM, and PC 315 with K(i) of 2.17 microM from Schizandra chinensis. PC 314 and PC 315 have been characterized as benzoylgomisin Q (M.W. 552) and gomisin G (M.W. 536). We report that PC 314 and PC 315 are the first non-peptide, natural compounds, which bind to human NPFF2 receptors with good affinity. PC 314 and PC 315 inhibit forskolin-stimulated luciferase expression when CHO cells are co-transfected with NPFF2 receptor and CRE reporter vector. They possess the pharmacological and functional profiles of full agonists. The FP HTS system provides a specific, sensitive and reproducible methodology for studying and screening NPFF receptor ligands.

Point mutation of (+)-germacrene A synthase from Ixeris dentata.

Sesquiterpene cyclases catalyze the conversion of common precursor, farnesyl pyrophosphate, into various terpene backbones. X-ray crystallography of tobacco epi-aristolochene synthase has previously proposed a cyclization mechanism wherein the allylic carbocation intermediate is stabilized by the main chain carbonyl oxygens of three consecutive threonine residues. Alignment of amino acid sequences of plant terpene cyclases shows that the first position of the triad is almost invariably threonine or serine. To probe the carbocation-stabilizing role, the amino acid residues of the 433TSA435 triad in (+)-germacrene A synthase from Ixeris dentata were altered by site-directed mutagenesis. Enzyme kinetic measurements of the mutants and GC/MS analysis of the enzyme reaction products indicate that mutations of the triad decreased enzyme catalysis rather than substrate binding but did not affect its structural rearrangement in the catalytic mechanism. This is the first report that the hydroxyl group of threonine at the first position of the triad is required for the cyclase activity.

Reverse transcription quantitative-PCR of three genes with high homology encoding 3-hydroxy-methylglutaryl-CoA reductase in rice.

Reverse transcription followed by RT Q-PCR is useful for the systematic measurement of changes in gene expression. RT Q-PCR with two pairs of primers for each gene was used for relative expression of three genes with high homology encoding 3-hydroxy-methylglutaryl-CoA reductase (HMGR) in rice. At various growth stages of etiolated seedling and various times after UV-irradiation treatment, RT Q-PCR of each HMGR gene showed a consistent pattern of relative expression with the RT Q-PCR data, using two pairs of primers, giving a high degree of accuracy. Furthermore, the different expression levels of three HMGR genes in a sample were determined by diluting the cDNA concentration. These results indicate that RT Q-PCR with only one pair of primers for a gene can quantify the relative expression and that the high expression level of HMGR2 could be quantified in comparison to the low level of HMGR1 expression.

Normalization of reverse transcription quantitative-PCR with housekeeping genes in rice.

Reverse transcription followed by real-time quantitative polymerase chain reaction (RT Q-PCR) is useful for the systematic measurement of plant physiological changes in gene expression. The validity of using 18S rRNA and three housekeeping genes, glyceraldehyde-3-phosphate dehydrogenase, actin, and tubulin, was tested as a reference of RT Q-PCR. Under various growth stages of etiolated seedlings, different cultivars, and various times after UV-irradiation treatment, expression level of 18S rRNA correlated with total RNA suggesting the uniformity of RT Q-PCR efficiencies among samples. Relative expressions of housekeeping genes varied among samples and independently of experimental conditions, up to two-fold, signifying generally constant fraction of mRNA in total RNA. Results indicate 18S rRNA was the most reliable reference gene for RT Q-PCR of total RNA.