The cyclic AMP system andDrosophila learning

Molecular and Cellular Biochemistry - The cyclic AMP (cAMP) system plays a critical role in olfactory learning in the fruit fly,Drosophila melanogaster, as evidenced by the following: [1] The dunce...     

Cell death in the thin films of bursting bubbles.

A sparged gas bubble floating at the liquid interface has a liquid film which drains and thins until the film spontaneously ruptures at a point. This causes rapid retraction of the film, forming a rim of collected fluid. This rim moves at a constant velocity of about 3 m/s and any cells in the bubble film are rapidly accelerated to this velocity in the moving rim. Half of the surface energy originally in the thin film is converted to kinetic energy of the rim, while the rest is dissipated in this rim. The rate of energy dissipation per mass of rim fluid is approximately 9000 m2/s3, which corresponds to a Kolmogorov eddy size of 3.2 microns in fully developed turbulence or a shear stress of 95 N/m2 in laminar flow. Either of these limiting cases presents an environment in which rapid cell death would be expected. Experiments with Sf-9 insect cells suggest that the cell concentration in these thin films is 0.6 times the bulk liquid concentration and that about 20% of these cells are killed when the film ruptures. An equation based on this mechanism accurately predicts the death rate.     

Molecular cloning of a cDNA encoding aspartate aminotransferase-P2 from lupin root nodules

Two isoenzymic forms of aspartate aminotransferase are present in the plant fraction of developing lupin root nodules. One of these forms, aspartate aminotransferase-P₂ (AAT-P₂), increases dramatically with the onset of biological nitrogen fixation and is associated with the assimilation of ammonia by the plant in the Rhizobium-legume symbiosis. A day 18 lupin nodule cDNA library in the ZapII vector was immunoscreened with a monoclonal antibody specific for AAT-P₂ and yielded two near-full-length 1700 bp clones. These clones were sequenced. Amino acid sequences from three peptides derived from immunopurified AAT-P₂ were aligned, and showed 100% homology with the amino acid sequence deduced from the cDNA clones. The DNA sequence showed 50% homology with AAT sequences from a range of animal sources. Conversion of the clones to the phagemid form allowed their expression in Escherichia coli where both exhibited enzyme activity that could be immunoprecipitated with AAT-P₂-specific monoclonal antibodies. Western blot analysis revealed protein moieties with molecular masses of 39, 43, 45 and 55 kDa. The 5 end of the clones coded for a hydrophobic leader sequence of about 50 amino acids indicative of a targeting sequence and consistent with the plastid localisation of nodule AAT-P₂.     

Novel biopolymers for drug discovery

The solid phase synthesis and generation of libraries of “unnatural biopolymers” is described. These polymers are characterized by novel backbones and building blocks, the properties of which may modify their pharmacological and folding properties. © 1994 John Wiley & Sons, Inc.     

Novel inhibitors of influenza sialidases related to GG167 structure-activity, crystallographic and Molecular dynamics studies with 4H-pyran-2-carboxylic acid 6-carboxamides

The structure-activity relationships of a series of 4-amino and guanidino-4H-pyran-2-carboxylic acid 6-carboxamides are described. These compounds represent a new class of inhibitor of influenza sialidases and are particularly active against influenza A sialidase. The binding of the N-phenethyl-N-propylamide 41 to influenza A and B sialidases has been investigated using X-ray crystallography and molecular dynamics simulations. Our results suggest that formation of a hitherto unobserved intramolecular salt bridge within the enzymes may account for the observed activity and selectivity of the series.     

Ligand binding sites for a synthetic B cell growth and differentiation factor

The mechanism of action of a group of synthetic lymphokine-like molecules, the C8-substituted guanine ribonucleosides, was studied. Among their pleiotropic effects on B cells are the increased expression of surface Ia antigens, induction of polyclonal immunoglobulin secretion, enhancement of thymus-dependent as well as thymus-independent antibody responses, and transmission of T cell-like differentiative signals to B cells. However, relatively little is known about their molecular mechanism of action. In the current article, the interaction of 8-bromo-guanosine (8BrGuo), a prototypical C8-substituted guanine ribonucleoside, with cellular components was examined. Rapidly exchangeable (free) and slowly exchangeable (bound) 8BrGuo pools exist within B cells. The bound nucleoside pool loses its ability to be retained by a boronate affinity resin (despite its resistance to metabolic processing) and localizes to the cytosol on sucrose density gradients. Binding affinity, ligand specificity, and cellular specificity of binding all correlate closely with observed functional properties of these molecules. Together, these data suggest that the binding interaction mediates the biologic activities of 8BrGuo, and that the binding site acts as a functional nucleoside receptor.