Sang Wan Gal

A new class II rice chitinase, Rcht2, whose induction by fungal elicitor is abolished by protein phosphatase 1 and 2A inhibitor

Among the four classes of chitinase, a class II chitinase had not yet been reported for rice. We have isolated and characterized a class II acidic chitinase, Rcht2, from rice (Oryza sativa L. cv. Cheongcheongbyeo). The protein consists of a single polypeptide chain of 261 amino acid residues and includes a putative signal sequence of 29 amino acids at its N-terminus. It has a calculated molecular mass of 27 642 Da and an isoelectric point of 5.56. The Rcht2 chitinase lacks the cysteine-rich and hinge domains in the N-terminal region of the protein, which is the criterion for its classification as a class II chitinase. Comparison of the genomic and the cDNA sequence revealed that the coding region of Rcht2 consist of three exons of 301, 112, and 370 bp separated by two introns of 89 and 984 bp. In suspension-cultured rice cells, the transcript level of Rcht2 was dramatically increased by treatment with both glycol chitin and fungal elicitor. The application of protein phosphatase 1 and 2A inhibitors, calyculin A and okadaic acid, effectively abolished the induction of Rcht2 in response to fungal elicitor. In contrast, the activation of Rcht2 transcript was not inhibited by both cycloheximide and protein kinase inhibitors. These results demonstrate that protein dephosphorylation events play a crucial role in the elicitor-mediated induction of Rcht2 in rice cells, while de novo protein synthesis is not required for induction.

Expression of a Chinese cabbage cysteine proteinase inhibitor, BrCYS1, retards seed germination and plant growth in transgenic Tobacco plant

Phytocystatins are plant cysteine proteinase inhibitors that regulate endogenous and heterologous cysteine proteinases of the papain family. A cDNA encoding the phytocystatin BrCYS1 (Brassica rapa cysteine proteinase inhibitor 1 ) has been isolated from Chinese cabbage (B. rapa subsp.pekinensis) flower buds. In order to explore the role of this inhibitory enzyme, tobacco plants (Nicotiana tabacum L. cv. Samson) containing altered amounts of phytocystatin were generated by over-expressingBrCYS1 cDNA in either the sense or the antisense configuration. The resulting plants hadin vitro enzyme inhibitory activities that were over 10% of those detected in wild type plants. The transgenic plants exhibited retarded seed germination and seedling growth and a reduced seed yield, whereas these properties were enhanced in antisense plants. These data suggest that BrCYS1 participates in the control of seed germination, post-germination and plant growth by regulating cysteine peptidase activity.

Antitumor Sterol Isolated from the Fruiting Body of Pleurotus eryngii

Activity-guided fractionations led to the isolation of antitumor compound, ergosterol peroxide (5α, 8α-epideoxy-24(R)-methylcholesta-6, 22-dien-3β-ol) from the fruiting body of Pleurotus eryngii that was cultivated artificially. This sterol structure was established by using spectroscopic methods (1H and ¹³C nuclear magnetic resonance and high resolution mass spectra). The purified compound showed a molecular formular of C 28 H₄₄O₃, displaying characteristic features of epidioxy sterols. The 50% inhibitory concentrations (IC 50 ) of ergosterol peroxide against human lung cancer cell line (A549) and human ovarian cell line (SK-OV3) were 7 μM and 14 μM, respectively. In the DNA fragmentation assay, the compound showed the programmed cell death causing the chromosomal DNA fragmentation. It reveals that ergosterol peroxide arrests G1 phase of the cell division cycle.

Tyrosinase Inhibitory Xanthones from Cudrania tricuspidata

The methanolic roots bark extract of Cudrania tricuspidata (Carr.) Bureau was chromatographed, which yielded three xanthones 1-3 by tyrosinase inhibitory activity-guided fractionation. The structures were fully characterized by analysis of physical and spectral data. Among them, furano prenylxanthone 3, never reported as tyrosinase inhibitor, showed potent activity with IC?? value of 16.5 μM, and appeared to inhibit the polyphenol oxidase activity of tyrosinase in an uncompetitive inhibitor (K i = 1.6 μM) when L-tyrosine was used as a substrate. Moreover, potent inhibitor furano prenylxanthone 3 had an extended lag time of 310 sec at 20 μM, while lag time of kojic acid as positive control was prolonged with 350 sec at the same concentration.