Copper-Triggered Aggregation of Ubiquitin

Neurodegenerative disorders share common features comprising aggregation of misfolded proteins, failure of the ubiquitin-proteasome system, and increased levels of metal ions in the brain. Protein aggregates within affected cells often contain ubiquitin, however no report has focused on the aggregation propensity of this protein. Recently it was shown that copper, differently from zinc, nickel, aluminum, or cadmium, compromises ubiquitin stability and binds to the N-terminus with 0.1 micromolar affinity. This paper addresses the role of copper upon ubiquitin aggregation. In water, incubation with Cu(II) leads to formation of spherical particles that can progress from dimers to larger conglomerates. These spherical oligomers are SDS-resistant and are destroyed upon Cu(II) chelation or reduction to Cu(I). In water/trifluoroethanol (80∶20, v/v), a mimic of the local decrease in dielectric constant experienced in proximity to a membrane surface, ubiquitin incubation with Cu(II) causes time-dependent changes in circular dichroism and Fourier-transform infrared spectra, indicative of increasing β-sheet content. Analysis by atomic force and transmission electron microscopy reveals, in the given order, formation of spherical particles consistent with the size of early oligomers detected by gel electrophoresis, clustering of these particles in straight and curved chains, formation of ring structures, growth of trigonal branches from the rings, coalescence of the trigonal branched structures in a network. Notably, none of these ubiquitin aggregates was positive to tests for amyloid and Cu(II) chelation or reduction produced aggregate disassembly. The early formed Cu(II)-stabilized spherical oligomers, when reconstituted in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and in POPC planar bilayers, form annular and pore-like structures, respectively, which are common to several neurodegenerative disorders including Parkinson's, Alzheimer's, amyotrophic lateral sclerosis, and prion diseases, and have been proposed to be the primary toxic species. Susceptibility to aggregation of ubiquitin, as it emerges from the present study, may represent a potential risk factor for disease onset or progression while cells attempt to tag and process toxic substrates

The Development of Language Learning Strategies

This article discusses the strategy repertoires and strategy development of six English children who learned foreign languages at primary school. My study differs from mainstream research in that it focuses on young children and on the development of their strategies, draws on sociocultural theory and uses ethnographic methods. My findings show that the six children developed a range of strategies over the course of a calendar year in spite of receiving no direct strategy instruction. The primary classroom encouraged learner autonomy and stimulated children to reflect on their learning which, in turn, enabled them to refine their strategies

The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites

Oxidation of NG-Hydroxy-L-arginine by Nitric Oxide Synthase: Evidence for the Involvement of the Heme in Catalysis

The involvement of the protoporphyrin IX heme iron of macrophage nitric oxide synthase (NOS) in the oxidation of NG-hydroxy-L-arginine (L-NHA) to nitric oxide (NO) and citrulline was investigated by carbon monoxide (CO) inhibition studies and binding difference spectroscopy. A CO:oxygen mixture (80:20) was found to inhibit the reaction by 33% with L-NHA as a substrate compared to 57% with L-arginine. Spectral perturbations were observed upon the addition of L-NHA to oxidized NOS, producing a type I binding difference spectrum with a maximum at 384 nm and minimum at 420 nm. In addition, L-NHA was incapable of reducing anaerobic oxidized NOS in the absence of NADPH. These studies support the involvement of the heme in the oxidation of L-NHA to NO and citrulline, indicating that the heme functions in both of the currently characterized oxidative steps of the NOS reaction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30734/3/0000383.pd