Synthesis and SAR of highly potent and selective dopamine D(3)-receptor antagonists: 1H-pyrimidin-2-one derivatives

The synthesis and SAR of novel highly potent and selective dopamine D(3)-receptor antagonists based on a 1H-pyrimidin-2-one scaffold are described. A-690344 antagonized PD 128907-induced huddling deficits in rat (ED(50) 6.1mg/kg po), a social interaction paradigm.     

Crystal Structure Determination and Functional Characterization of the Metallochaperone SlyD from Thermus thermophilus

SlyD (sensitive to lysis D; product of the slyD gene) is a prolyl isomerase [peptidyl-prolyl cis/trans isomerase (PPIase)] of the FK506 binding protein (FKBP) type with chaperone properties. X-ray structures derived from three different crystal forms reveal that SlyD from Thermus thermophilus consists of two domains representing two functional units. PPIase activity is located in a typical FKBP domain, whereas chaperone function is associated with the autonomously folded insert-in-flap (IF) domain. The two isolated domains are stable and functional in solution, but the presence of the IF domain increases the PPIase catalytic efficiency of the FKBP domain by 2 orders of magnitude, suggesting that the two domains act synergistically to assist the folding of polypeptide chains. The substrate binding surface of SlyD from T. thermophilus was mapped by NMR chemical shift perturbations to hydrophobic residues of the IF domain, which exhibits significantly reduced thermodynamic stability according to NMR hydrogen/deuterium exchange and fluorescence equilibrium transition experiments. Based on structural homologies, we hypothesize that this is due to the absence of a stabilizing β-strand, suggesting in turn a mechanism for chaperone activity by ‘donor-strand complementation.’ Furthermore, we identified a conserved metal (Ni²⁺) binding site at the C-terminal SlyD-specific helical appendix of the FKBP domain, which may play a role in metalloprotein assembly.     

Normal reproductive function in InhBP/p120-deficient mice

The inhibins are gonadal transforming growth factor beta superfamily protein hormones that suppress pituitary follicle-stimulating hormone (FSH) synthesis. Recently, betaglycan and inhibin binding protein (InhBP/p120, also known as the product of immunoglobulin superfamily gene 1 [IGSF1]) were identified as candidate inhibin coreceptors, shedding light on the molecular basis of how inhibins may affect target cells. Activins, which are structurally related to the inhibins, act within the pituitary to stimulate FSH production. Betaglycan increases the affinity of inhibins for the activin type IIA (ACVR2) receptor, thereby blocking activin binding and signaling through this receptor. InhBP/p120 may not directly bind inhibins but may interact with the activin type IB receptor, ALK4, and participate in inhibin B's antagonism of activin signaling. To better understand the in vivo functions of InhBP/p120, we characterized the InhBP/p120 mRNAs and gene in mice and generated InhBP/p120 mutant mice by gene targeting in embryonic stem cells. InhBP/p120 mutant male and female mice were viable and fertile. Moreover, they showed no alterations in FSH synthesis or secretion or in ovarian or testicular function. These data contribute to a growing body of evidence indicating that InhBP/p120 does not play an essential role in inhibin biology.     

High-throughput viral expression of cDNA-green fluorescent protein fusions reveals novel subcellular addresses and identifies unique proteins that interact with plasmodesmata

A strategy was developed for the high-throughput localization of unknown expressed proteins in Nicotiana benthamiana. Libraries of random, partial cDNAs fused to the 5' or 3' end of the gene for green fluorescent protein (GFP) were expressed in planta using a vector based on Tobacco mosaic virus. Viral populations were screened en masse on inoculated leaves using a confocal microscope fitted with water-dipping lenses. Each viral infection site expressed a unique cDNA-GFP fusion, allowing several hundred cDNA-GFP fusions to be screened in a single day. More than half of the members of the library carrying cDNA fusions to the 5' end of gfp that expressed fluorescent fusion proteins displayed discrete, noncytosolic, subcellular localizations. Nucleotide sequence determination of recovered cDNA sequences and subsequent sequence searches showed that fusions of GFP to proteins that had a predicted subcellular "address" became localized with high fidelity. In a subsequent screen of >20,000 infection foci, 12 fusion proteins were identified that localized to plasmodesmata, a subcellular structure for which very few protein components have been identified. This virus-based system represents a method for high-throughput functional genomic study of plant cell organelles and allows the identification of unique proteins that associate with specific subcompartments within organelles.     

Conditioned medium from cultured rat hepatocytes completely blocks induction of glutamine synthetase by dexamethasone in several rat liver epithelial cell lines

A variant RL-ET-1G of a rat liver epithelial cell line (RL-ET-1) characterized by a very high inducibility for glutamine synthetase (GS) in response to dexamethasone was established by cultivation in glutamine-free, glutamate-supplemented culture medium. Using this cell line, conditioned medium produced by periportal hepatocytes in primary culture was found to suppress this induction, acting with a lag-phase of about 8 h irrespective whether the GS activity was basal or preinduced. Analysis of the response of several epithelial cell lines to the conditioned medium showed a reciprocal relationship between the dexamethasone-dependent induction and the residual activity after exposure to the conditioned medium, indicating that a hypothetical factor in the conditioned medium was interfering with the induction process but not with the basal GS level of these cells. Careful analysis revealed that the effect of the conditioned medium was neither due to deficiency of a component used up by the hepatocytes, nor due to glutamine or ammonia, both of which affected GS activity at concentrations above 0.5 mmol/L. The hypothetical factor was found to be quite small (molecular mass range 100–500 Da), heat and acid stable, as well as highly water soluble. Most interestingly, the conditioned medium did not suppress GS induction in astroglial cells and in the two hepatoma cell lines C2 and FAO, but strongly diminished the spontaneous induction of GS in cocultured pig hepatocytes, suggesting that the hypothetical factor acts primarily on normal nontransformed liver-derived cell populations.     

Nucleotide sequence ofbup,an upstream gene in thebmi-1 proviral insertion locus

The ability of Moloney murine leukemia virus to accelerate lymphomagenesis in E-myc transgenic mice is frequently associated with proviral integration within a locus denotedbmi-1. This locus contains not only thebmi-1 gene implicated as a collaborator withmyc in lymphomagenesis but also just upstream an unknown gene denotedbup. The nucleotide sequence reported here forbup cDNA and flanking genomic sequences reveals that this widely expressed gene comprises at least 7 exons and potentially encodes a polypeptide of 195 amino acid residues. Computer searches with this polypeptide sequence revealed no close homolog in the databases, nor any conserved motifs, and it is unrelated to the product of themel-13 gene, which lies just upstream from thebmi-1 homologmel-18.