Evidence for an increased rate of choline efflux across erythrocyte membranes in Alzheimer's disease

Alzheimer's disease (AD), the major dementing disorder of the elderly, is associated with cholinergic neuronal loss and decreased activity of choline acetyl-transferase (CAT). Previous biophysical studies had suggested an altered conformation of membrane proteins in AD erythrocyte ghosts. Since erythrocytes have a choline transport system and cholinergic neurons are implicated in AD, the present experiments were undertaken to determine if the efflux rate of [¹⁴C]choline was altered in AD erythrocytes. The mean efflux rate constant was highly significantly increased (P<0.01) by greater than 25% in 9 drug-free AD patients compared to 9 sex-matched, drug-free controls of similar age. These results are discussed in terms of potential molecular mechanisms to account for cholinergic neuronal loss in AD.     

Functional analysis of lipid metabolism in Magnaporthe grisea reveals a requirement for peroxisomal fatty acid beta-oxidation during appressorium-mediated plant infection

The rice blast fungus Magnaporthe grisea infects plants by means of specialized infection structures known as appressoria. Turgor generated in the appressorium provides the invasive force that allows the fungus to breach the leaf cuticle with a narrow-penetration hypha gaining entry to the underlying epidermal cell. Appressorium maturation in M. grisea involves mass transfer of lipid bodies to the developing appressorium, coupled to autophagic cell death in the conidium and rapid lipolysis at the onset of appressorial turgor generation. Here, we report identification of the principal components of lipid metabolism in M. grisea based on genome sequence analysis. We show that deletion of any of the eight putative intracellular triacylglycerol lipase-encoding genes from the fungus is insufficient to prevent plant infection, highlighting the complexity and redundancy associated with appressorial lipolysis. In contrast, we demonstrate that a peroxisomally located multifunctional, fatty acid beta-oxidation enzyme is critical to appressorium physiology, and blocking peroxisomal biogenesis prevents plant infection. Taken together, our results indicate that, although triacylglycerol breakdown in the appressorium involves the concerted action of several lipases, fatty acid metabolism and consequent generation of acetyl CoA are necessary for M. grisea to complete its prepenetration phase of development and enter the host plant.     

The alteration of membrane proteins in human erythrocyte membranes induced by quinolinic acid, an endogenous neurotoxin. Correlation of effect with structure

Mixtures containing subfractions of human plasma high-density lipoproteins (HDL) and human lipoprotein-free plasma were incubated in vitro at 37 degrees C. Esterification of cholesterol was observed both in incubations containing HDL-subfraction 3 (HDL3) and in those containing HDL-subfraction 2 (HDL2). The implication that the lecithin: cholesterol acyltransferase in lipoprotein-free plasma may therefore interact with lipoproteins in both HDL subfractions was developed further by proposing a simple model in which the two HDL subfractions may compete for interactions with the enzyme. This model was described mathematically and tested in experiments in which a constant amount of the enzyme was incubated with a wide range of concentrations of HDL2 and HDL3 present either alone or in combination. The model was able to predict experimentally observed rates of cholesterol esterification with great accuracy. The best fit was obtained with a Vmax for HDL3 that was 2.4-4-times greater than that for HDL2 and values of the apparent Km for HDL3 free cholesterol and HDL2 free cholesterol of 43-60 nmol/ml and 167-391 nmol/ml, respectively. The model thus predicts that, at physiological concentrations of lipoproteins, HDL2 will function as a competitive inhibitor of the cholesterol esterification reaction by displacing lecithin: cholesterol acyltransferase from a more effective substrate, HDL3, to a less effective substrate, HDL2.     

Targeting conserved water molecules: Design of 4-aryl-5-cyanopyrrolo[2,3-d]pyrimidine Hsp90 inhibitors using fragment-based screening and structure-based optimization

Inhibitors of the Hsp90 molecular chaperone are showing promise as anti-cancer agents. Here we describe a series of 4-aryl-5-cyanopyrrolo[2,3-d]pyrimidine ATP competitive Hsp90 inhibitors that were identified following structure-driven optimization of purine hits revealed by NMR based screening of a proprietary fragment library. Ligand-Hsp90 X-ray structures combined with molecular modeling led to the rational displacement of a conserved water molecule leading to enhanced affinity for Hsp90 as measured by fluorescence polarization, isothermal titration calorimetry and surface plasmon resonance assays. This displacement was achieved with a nitrile group, presenting an example of efficient gain in binding affinity with minimal increase in molecular weight. Some compounds in this chemical series inhibit the proliferation of human cancer cell lines in vitro and cause depletion of oncogenic Hsp90 client proteins and concomitant elevation of the co-chaperone Hsp70. In addition, one compound was demonstrated to be orally bioavailable in the mouse. This work demonstrates the power of structure-based design for the rapid evolution of potent Hsp90 inhibitors and the importance of considering conserved water molecules in drug design.     

The nematode fauna of a temperate Australian mangrove mudflat; its population density,diversity and distribution

The nematode fauna of an estuarine mangrove Avicennia marina mudflat in Southeastern Australia has been intensively studied. About 85% of the nematodes occur in the top cm of soft mud, but 5–7 species inhabit the deeper anoxic mud down to 10 cm, both at low and high tide. One square metre was intensively sampled from four zones with different nematode faunas. At the low tide zone 58% of the nematodes were epistrate feeders, including many diatom-feeders, but in the mangrove zone selective microbial feeders made up over 60% of the population, while between high water neap and high water spring, above the mangrove zone, omnivore/predators and plant root feeding nematodes increased in relative importance. Random replicate cores reliably sampled species occurrence, but gave a high variance in density estimates. Replicate aliquots from homogenised mud gave lower density variance. Nematode densities (maximum 5 × 10⁶ m^-2) were not as high as have been reported from non-mangrove estuaries in other countries, but were within the range found in mangroves elsewhere in Australia. Margalef Species Richness values ranged from 1.7 to 3.89, which is similar to values found in other mangroves mudflats in Australia. Nematode biomass ranged from 888 mg dry weight m² (383 mg C m^-2) at the low tide zone to 19 mg dry weight m^-2 (8 mg C m^-2) at the upper tide level.     

Prospective Large-Scale Field Study Generates Predictive Model Identifying Major Contributors to Colony Losses

Over the last decade, unusually high losses of colonies have been reported by beekeepers across the USA. Multiple factors such as Varroa destructor, bee viruses, Nosema ceranae, weather, beekeeping practices, nutrition, and pesticides have been shown to contribute to colony losses. Here we describe a large-scale controlled trial, in which different bee pathogens, bee population, and weather conditions across winter were monitored at three locations across the USA. In order to minimize influence of various known contributing factors and their interaction, the hives in the study were not treated with antibiotics or miticides. Additionally, the hives were kept at one location and were not exposed to potential stress factors associated with migration. Our results show that a linear association between load of viruses (DWV or IAPV) in Varroa and bees is present at high Varroa infestation levels (>3 mites per 100 bees). The collection of comprehensive data allowed us to draw a predictive model of colony losses and to show that Varroa destructor, along with bee viruses, mainly DWV replication, contributes to approximately 70% of colony losses. This correlation further supports the claim that insufficient control of the virus-vectoring Varroa mite would result in increased hive loss. The predictive model also indicates that a single factor may not be sufficient to trigger colony losses, whereas a combination of stressors appears to impact hive health.     

Gill morphometrics of the thresher sharks (Genus Alopias): Correlation of gill dimensions with aerobic demand and environmental oxygen

Gill morphometrics of the three thresher shark species (genus Alopias) were determined to examine how metabolism and habitat correlate with respiratory specialization for increased gas exchange. Thresher sharks have large gill surface areas, short water–blood barrier distances, and thin lamellae. Their large gill areas are derived from long total filament lengths and large lamellae, a morphometric configuration documented for other active elasmobranchs (i.e., lamnid sharks, Lamnidae) that augments respiratory surface area while limiting increases in branchial resistance to ventilatory flow. The bigeye thresher, Alopias superciliosus, which can experience prolonged exposure to hypoxia during diel vertical migrations, has the largest gill surface area documented for any elasmobranch species studied to date. The pelagic thresher shark, A. pelagicus, a warm‐water epi‐pelagic species, has a gill surface area comparable to that of the common thresher shark, A. vulpinus, despite the latter's expected higher aerobic requirements associated with regional endothermy. In addition, A. vulpinus has a significantly longer water–blood barrier distance than A. pelagicus and A. superciliosus, which likely reflects its cold, well‐oxygenated habitat relative to the two other Alopias species. In fast‐swimming fishes (such as A. vulpinus and A. pelagicus) cranial streamlining may impose morphological constraints on gill size. However, such constraints may be relaxed in hypoxia‐dwelling species (such as A. superciliosus) that are likely less dependent on streamlining and can therefore accommodate larger branchial chambers and gills. J. Morphol. 276:589–600, 2015. © 2015 Wiley Periodicals, Inc.     

Novel Translation Products from Simian Immunodeficiency Virus SIVmac239 Env-Encoding mRNA Contain both Rev and Cryptic T-Cell Epitopes

Understanding the correlates of immune protection against human immunodeficiency virus and simian immunodeficiency virus (SIV) will require defining the entire cellular immune response against the viruses. Here, we define two novel translation products from the SIV env mRNA that are targeted by the T-cell response in SIV-infected rhesus macaques. The shorter product is a subset of the larger product, which contains both the first exon of the Rev protein and a translated portion of the rev intron. Our data suggest that the translation of viral alternate reading frames may be an important source of T-cell epitopes, including epitopes normally derived from functional proteins.The pathway from viral infection to the cellular immune response is not well understood. Despite the importance of T-cell responses in control of AIDS virus replication (1, 3, 8, 22), the sources of the peptides recognized by virus-specific T cells are still being discovered. AIDS virus-specific CD8⁺ T lymphocytes (CD8-TL) recognize complexes of major histocompatibility complex (MHC) class I and virus-derived epitopes presented on the surface of infected cells. These epitopes can be derived from exogenous viral proteins in the infecting virion (19, 20) or from de novo synthesis of viral proteins (9, 21). Additional sources of epitopes are also being explored (4, 6).CD8-TL can also recognize epitopes derived from translation of viral alternate reading frames (ARFs). Though CD8-TL specific for ARF-derived epitopes have been detected in human immunodeficiency virus (HIV) (2), they remain a largely unexplored source of epitopes that might elicit potent antiviral cellular immune responses. We recently showed that SIVmac239-infected rhesus macaques that spontaneously controlled viral replication, termed elite controllers, made immunodominant CD8-TL responses against an epitope (RHLAFKCLW, or cRW9) derived from an ARF of the env gene (15). This response selected for viral escape in vivo and suppressed viral replication in an in vitro assay. These findings imply that CD8-TL specific for ARF-derived epitopes might be an important component of the total AIDS virus-specific cellular immune response.Here, we show that the cRW9 epitope is translated as part of two distinct products that differ in size due to start codon usage. The larger and more frequent product contains both the first 23 amino acids of the Rev protein (exon 1) and 50 amino acids translated from the rev intron. The smaller is produced by translation initiation at a start codon within the rev intron and is a subset of the larger product. Finally, we show that these products are degraded after translation from the mature Env-encoding mRNA.     

Crystal structure of Leishmania major oligopeptidase B gives insight into the enzymatic properties of a trypanosomatid virulence factor

Oligopeptidase B (OPB) is a serine peptidase with dibasic substrate specificity. It is found in bacteria, plants, and trypanosomatid pathogens, where it has been identified as a virulence factor and potential drug target. In this study we expressed active recombinant Leishmania major OPB and provide the first structure of an oligopeptidase B at high resolution. The crystallographic study reveals that OPB comprises two domains, a catalytic and a propeller domain, linked together by a hinge region. The structure has been determined in complex with the oligopeptide, protease-inhibitor antipain, giving detailed information on the enzyme active site and extended substrate binding pockets. It shows that Glu-621 plays a critical role in the S1 binding pocket and, along with Phe-603, is largely responsible for the enzyme substrate specificity in P1. In the S2 binding pocket, Tyr-499 was shown to be important for substrate stability. The structure also allowed an investigation into the function of residues highlighted in other studies including Glu-623, which was predicted to be involved in the S1 binding pocket but is found forming an inter-domain hydrogen bond. Additional important salt bridges/hydrogen bonds between the two domains were observed, highlighting the significance of the domain interface in OPB. This work provides a foundation for the study of the role of OPBs as virulence factors in trypanosomatids. It could facilitate the development of specific OPB inhibitors with therapeutic potential by exploiting its unique substrate recognition properties as well as providing a model for OPBs in general.