Solid-state magic-angle spinning NMR of outer-membrane protein G from Escherichia coli

Uniformly 13C-,15N-labelled outer-membrane protein G (OmpG) from Escherichia coli was expressed for structural studies by solid-state magic-angle spinning (MAS) NMR. Inclusion bodies of the recombinant, labelled protein were purified under denaturing conditions and refolded in detergent. OmpG was reconstituted into lipid bilayers and several milligrams of two-dimensional crystals were obtained. Solid-state MAS NMR spectra showed signals with an apparent line width of 80-120 Hz (including homonuclear scalar couplings). Signal patterns for several amino acids, including threonines, prolines and serines were resolved and identified in 2D proton-driven spin-diffusion (PDSD) spectra.     

Solutions of the BCM learning rule in a network of lateral interacting nonlinear neurons.

We introduce a new method for obtaining the fixed points for neurons that follow the BCM learning rule. The new formalism, which is based on the objective function formulation, permits analysis of a laterally connected network of nonlinear neurons and allows explicit calculation of the fixed points under various network conditions. We show that the stable fixed points, in terms of the postsynaptic activity, are not altered by the lateral connectivity or nonlinearity. We show that the lateral connectivity alters the probability of attaining different states in a network of interacting neurons. We further show the exact alteration in presynaptic weights as a result of the neuronal nonlinearity.     

Effect of notch severity on fatigue fracture in a rubber-modified glassy polymer

The research concerned the effect of notch severity on the fatigue behaviour of series of rubber-modified glassy polymers, consisting of a styrene-acrylonitrile copolymer with different amounts of an olefin rubber. Tests were conducted under displacement control and two different loading conditions. Both stages of fatigue lifetimes, that is, fracture initiation and crack propagation, were examined. It was observed that the initial notch severity determines the duration of the crack-initiation stage, while crack propagation does not depend on it. The crack velocity appears to be controlled by the maximum applied stress intensity factor, and the correlation does not depend on the rubber content. The results obtained have been interpreted by considering three different zones in the specimen during the fracture process: a far-field viscoelastic continuum, a process zone and a failure zone.     

Molecular Pathogenesis of Alzheimer��s Disease: Reductionist versus Expansionist Approaches

Alzheimer’s disease (AD) is characterized clinically by dementia and pathologically by two hallmark lesions, senile plaques and neurofibrillary tangles. About a quarter century ago these hallmark lesions were purified and their protein constituents identified, precipitating an avalanche of molecular studies as well as substantial optimism about successful therapeutic intervention. In 2009, we now have copious knowledge on the biochemical cascades that produce these proteins, the different modifications and forms in which these proteins exist, and the ability to selectively target these proteins for therapeutic intervention on an experimental basis. At the same time, there has been no discernible alteration in the natural course of AD in humans. While it may be that the complexity of AD will exceed our capacity to make significant treatment progress for decades or more, a paradigm shift from the reductionism that defines amyloid-β and tau hypotheses, to one that more accurately reflects the meaning of neuropathological changes, may be warranted. We and others have demonstrated that AD pathology is a manifestation of cellular adaptation, specifically as a defense against oxidative injury. As such, AD pathology is therefore a host response rather than a manifestation of cytotoxic protein injury, and is unlikely to be a fruitful target for therapeutic intervention. An “expansionist” view of the disease, we believe, with oxidative stress as a pleiotropic and upstream process, more aptly describes the relationship between various and numerous molecular alterations and clinical disease.     

Concentration-dependent effects of eicosapentaenoic acid on very low density lipoprotein secretion by the isolated perfused rat liver

The effects of increasing concentrations of eicosapentaenoic acid (20∶5n?3; EPA) and oleic acid (18∶1n?9; OA) on esterification to triacylglycerols (TG) and phospholipids (PL), and the relationship to formation and secretion of the very low density lipoproteins (VLDL) were compared in the isolated perfused rat liver. Mixtures of EPA and OA were also studied to determine whether substrate levels of one fatty acid might influence the metabolism of the other. The basal perfusion medium, which contained 30% (vol/vol) washed bovine erythrocytes, 6% (wt/vol) bovine serum albumin (BSA), and 100 mg glucose/dL in Krebs-Henseleit bicarbonate buffer (pH 7.4) was recycled through the liver for 2 h. EPA or OA, as a complex with 6% BSA, was infused at rates of 70, 105, 140 and 210 μmol/h. In other experiments, mixtures of EPA and oleic acid (70 μmol total), with molar percentages of 100, 75, 50, 25 and 0% of each fatty acid were infused per hour. BSA (6%) in the buffer was infused alone and served as the control. At an infusion rate of 70 μmol EPA per hour, hepatic VLDL lipid output was not different from that when fatty acid was not infused (approximately half that when 70 μmol OA/h was infused). However, when larger amounts of EPA and OA were infused individually, rates of VLDL secretion were stimulated to a similar extent with either fatty acid. The apparent inhibitory influence of EPA on TG synthesis and VLDL lipid output when 70 μmol EPA were infused per hour could also be overcome by the presence of as little as 25 mol% OA in a mixture. Furthermore, the presence of EPA in the infused fatty acid mixture stimulated the incorporation of OA into TG, enhancing VLDL secretion. When EPA or OA was infused at rates exceeding 70 μmol/h, a constant amount of endogenously-derived fatty acids was incorporated into VLDL-TG, similar in amount to that when exogenous fatty acid was not supplied. However, when EPA was infused at a rate of 70 μmol/h, incorporation of endogenous fatty acid was depressed. AT this low rate of EPA infusion, esterification of EPA and endogenous fatty acid was inhibited. Conceivably, this may reflect the existence of independently-regulated pools of fatty acid (exogenous and endogenous), in that only exogenously available fatty acid preferentially enrich the secreted TG. Enrichment of PL by the infused fatty acid at the higher rates of fatty acid infusion showed similar, but much less pronounced, differences between VLDL and liver, compared to that for TG, providing additional evidence for a distinct metabolic pool of PL used for VLDL fabrication. It now appears that when EPA is available to the liver in high enough concentrations, or when OA (or other fatty acids?) is present in substrate amounts along with EPA, competing reactions and/or specific inhibitory influences of EPA on enzymatic reactions are overcome, and EPA can be utilized in a manner similar to OA for esterification to TG with subsequent enhanced VLDL formation and secretion.