In an effort to find potent inhibitors of the antiapoptotic protein Bcl-xL, a systematic in vitro evaluation was undertaken on 1470 Malaysian plant extracts. The ethyl acetate extract obtained from the bark of Meiogyne cylindrocarpa was selected for its interaction with the Bcl-xL/Bak association. Bioassay-guided purification of this species led to the isolation of two new dimeric sesquiterpenoids (1 and 2) possessing an unprecedented substituted cis-decalin carbon skeleton. Meiogynin A (1) showed the strongest activity with a K(i) of 10.8 +/- 3.1 microM.

The protein kinase CDK5 (cyclin-dependent kinase 5) is activated through its association with a cyclin-like protein p35 or p39. In pathological conditions (such as Alzheimer's disease and various other neuropathies), truncation of p35 leads to the appearance of the p25 protein. The interaction of p25 with CDK5 up-regulates the kinase activity and modifies the substrate specificity. ATP-mimetic inhibitors of CDK5 have already been developed. However, the lack of selectivity of such inhibitors is often a matter of concern. An alternative approach can be used to identify highly specific inhibitors that disrupt protein interactions involving protein kinases. We have developed a bioluminescence resonance energy transfer (BRET)-based screening assay in yeast to discover protein-protein interaction inhibitors (P2I2). Here, we present the first use of BRET in yeast for the screening of small molecule libraries. This screening campaign led to the discovery of one molecule that prevents the interaction between CDK5 and p25, thus inhibiting the protein kinase activity. This molecule may give rise to high-specificity drug candidates.

SUMMARYFaced with declining soil-water potential, plants synthesize abscisic acid (ABA), which then triggers stomatal closure to conserve tissue moisture. Closed stomates, however, also create several physiological dilemmas. Among these, the large CO 2 influx required for net photosynthesis will be disrupted. Depleting CO 2 in the plant will in turn bias stomatal opening by suppressing ABA sensitivity, which then aggravates transpiration further. We have investigated the molecular basis of how C3 plants resolve this H 2 O-CO 2 conflicting priority created by stomatal closure. Here, we have identified in Arabidopsis thaliana an early droughtinduced spermidine spermine-N 1 -acetyltransferase homolog, which can slow ABA-mediated stomatal closure. Evidence from genetic, biochemical and physiological analyses has revealed that this protein does so by acetylating the metabolite 1,3-diaminopropane (DAP), thereby turning on the latter's intrinsic activity. Acetylated DAP triggers plasma membrane electrical and ion transport properties in an opposite way to those by ABA. Thus in adapting to low soil-water availability, acetyl-DAP could refrain stomates from complete closure to sustain CO 2 diffusion to photosynthetic tissues.