No abstract

Polo-like kinase 1 (Plk1) is a serine-threonine protein kinase that possesses many essential functions during mitosis and is one of the key regulators of mitotic cell division. 1,2 Although it has a catalytic domain of protein kinase at its N-terminus, it possesses a phosphopeptide binding domain named polo box domain (PBD) at its C-terminus. 3,4 PBD binds to other protein in a phosphorylation dependent manner. PBD-dependent binding not only is important for the subcellular localization, but is also necessary for the targeting of Plk1 to specific substrates. 3 Plk1 is frequently overexpressed in many cancers and inhibition of Plk1 by antisence oligonucleotides or small interfering RNA (siRNA) is highly effective in inhibiting cancer cell proliferation. The reduction of Plk1 is also shown to induce tumor regression in mouse xenograft model. 5 Thus, Plk1 is considered to be an attractive target for the treatment of human cancers. [6][7][8] Several inhibitors of its catalytic activity are developed and some of them have proceeded to clinical trials. 9,10 We established a screening system for the inhibitors of PBD-dependent binding. 11 In this system, the open reading frame of a green fluorescent protein (GFP) is fused to PBD and expressed in bacteria. Target phosphopeptides for the PBD binding sequence are chemically synthesized and bound covalently to maleimide-activated 96-well plates. The binding of GFP-PBD to the phosphopeptides was quantitated through spectrofluorometry. Using this system, we have obtained purpurogallin, a benzotropolone-containing natural compound from nutgalls as an inhibitor of PBD. 11 Several other inhibitors of PBD are also identified by other groups but currently no clinical trials have been reported. 12 We have developed a structure based compound isolation technique named NPPlot (Natural Products Plot), where secondary metabolites from microorganisms are analyzed by their MW and retention time on DAD-LC/MS. 13 These analytical data are accumulated and used for the spectral database establishment. Using the method, we have isolated several new metabolites with unprecedented skeletons from microbial sources, such as verticilactam, 14 spirotoamides, 15 pyrrolizilactone 16 and recently opantimycin A. 17 In the present study, we combined our high-throughput screening system for PBD inhibitors and the methodology of the fractionation of microbial metabolites with spectral database. Using these techniques, a new 5,5-spiroacetal metabolite, trachyspic acid 19-butyl ester (1) together with a known metabolite trachyspic acid (2) 18 with potent PBD inhibitory activity was isolated from uncharacterized fungus RKGS-F2684 (Figure 1). We report here the isolation, structure and biological activity of 1.In the course of screening from about 3000 microbial extracts using our high-throughput screening system, we found that the extracts from fungal strain RKGS-F2684, which was isolated from a soil sample collected in Kumamoto, Japan in 1995, contained potent inhibitory activity. An ethyl acetate sol...

Hawaii yellow-eyed grass (Xyris complanata: Xyridaceae) inhabits infertile, acidic peat soil in the rainy tropical zone in Southeast Asia. This monocot plant produces a large number of dormant seeds in order to make a large deposit to seed bank in the soil. Under laboratory conditions, surface-sterilized X. complanata seeds are rarely able to germinate on sterilized peat moss bed; they require inoculation with either seed epiphytic or soil fungi to facilitate active seed germination. In the present study, three different genera of seed epiphytic fungi were isolated, and two common fungal genera, Fusarium sp. (strain R-1) and Penicillium sp. (strain Y-1), were found to promote seed germination of X. complanata. In sterile peat moss beds, the germination-stimulating fungi also showed growth-promoting effects on X. complanata seedlings. These results suggest that the seed germination-promoting fungi likely function as genuine partners for X. complanata in tropical open peat lands.

A B S T R A C T L o w -c o s t f o r e s t m a nThe most prominent strain isolated from Shorea leprosula was Erwinia. Other effective isolates were tentatively identified as, Rhizobium , Enterobacter , Duganella , an Alcaligeneceae bacterium, an Oxalobacteraceae bacterium, and some yeasts.