Mechanism of prion propagation: amyloid growth occurs by monomer addition

Abundant nonfibrillar oligomeric intermediates are a common feature of amyloid formation, and these oligomers, rather than the final fibers, have been suggested to be the toxic species in some amyloid diseases. Whether such oligomers are critical intermediates for fiber assembly or form in an alternate, potentially separable pathway, however, remains unclear. Here we study the polymerization of the amyloidogenic yeast prion protein Sup35. Rapid polymerization occurs in the absence of observable intermediates, and both targeted kinetic and direct single-molecule fluorescence measurements indicate that fibers grow by monomer addition. A three-step model (nucleation, monomer addition, and fiber fragmentation) accurately accounts for the distinctive kinetic features of amyloid formation, including weak concentration dependence, acceleration by agitation, and sigmoidal shape of the polymerization time course. Thus, amyloid growth can occur by monomer addition in a reaction distinct from and competitive with formation of potentially toxic oligomeric intermediates.     

Ethanol formation and enzyme activities around glucose-6-phosphate in Kluyveromyces marxianus CBS 6556 exposed to glucose or lactose excess

The aim of this work was to investigate the physiology of Kluyveromyces marxianus CBS 6556 in terms of its low tendency to form ethanol under exposure to sugar excess, and the split of carbon flux which takes place at the level of glucose-6-phosphate. Measurements were performed in batch cultivations, and after a glucose or a lactose pulse applied to chemostat-grown respiring cells (with a dilution rate of 0.1 h(-1)). No ethanol formation was observed in batch cultivations or during pulse experiments, unless the oxygen supply was shut down, indicating that this organism is more strictly Crabtree-negative than its close relative K. lactis and other known Crabtree-negative yeasts. During the pulse experiments, activities of phosphoglucoisomerase, glucose-6-phosphate dehydrogenase and phosphoglucomutase in cell-free extracts remained rather constant, at higher levels than those of Saccharomyces cerevisiae grown at similar conditions. When cells were exposed to glucose concentrations as high as 26 gl(-1), the activity of phosphoglucomutase was higher than that in cells exposed to 14 gl(-1) glucose, whereas the activities of phosphoglucoisomerase and glucose-6-phosphate dehydrogenase did not change. Our results suggest that the low tendency for ethanol formation in K. marxianus might be a consequence of this yeast's capacity of keeping the glycolytic flux constant, due at least in part to the diversion of carbon flux towards the biosynthesis of carbohydrates and towards the pentose phosphate pathway.     

Three-phase partitioning as an efficient method for extraction/concentration of immunoreactive excreted-secreted proteins of Corynebacterium pseudotuberculosis

The three-phase partitioning (TPP) technique was used upstream to isolate/concentrate secreted proteins from Corynebacterium pseudotuberculosis cultured in a complex liquid medium. Several parameters of the TPP technique (15, 30, or 60% ammonium sulfate concentration; 4.0, 5.5, or 7.0 pH; and primary (n) or tertiary (t)-butanol solvent isomer) were varied to determine the optimal recovery of serologically and cellularly immunoreactive extracted proteins. A TPP extraction made with 30% ammonium sulfate and an initial pH of 4.0 gave the best humoral and cellular immunoreactivity of caseous lymphadenitis infected goats. In particular, two immunogenic secreted (16 and 125 kDa) proteins, which had not been found by other extraction methods, were identified.     

Modeling protein complexes with BiGGER

This article describes the method and results of our participation in the Critical Assessment of PRediction of Interactions (CAPRI) experiment, using the protein docking program BiGGER (Bimolecular complex Generation with Global Evaluation and Ranking) (Palma et al., Proteins 2000;39:372-384). Of five target complexes (CAPRI targets 2, 4, 5, 6, and 7), only one was successfully predicted (target 6), but BiGGER generated reasonable models for targets 4, 5, and 7, which could have been identified if additional biochemical information had been available.     

Mitochondrial apoptotic cell death and moderate superoxide generation upon selective activation of non-desensitizing AMPA receptors in hippocampal cultures

In the present work we investigated the effect of selective stimulation of non-desensitizing alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors in the intracellular processes leading to hippocampal neuronal death and production of reactive oxygen species (ROS). Activation of AMPA receptors in the presence of cyclothiazide (CYZ), a blocker of AMPA receptor desensitization, resulted in the death of approximately 25% of neurones, which was prevented by 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(f)quinoxaline (NBQX), an AMPA-preferring receptor antagonist. (+)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) protected the neurones from necrotic death induced by AMPA or NMDA receptor activation. Neurodegeneration caused by selective activation of non-desensitizing AMPA receptors, in the presence of AMPA, CYZ and MK-801, significantly decreased the number of Co2+-positive neurones, used as a cytochemical marker of Ca2+-permeable AMPA receptors, but maintained intracellular ATP/ADP. The AMPA-mediated apoptotic cell death involved mitochondrial cytochrome c release and the activation of caspases-1 and -3, which was prevented by NBQX. Interestingly, although selective activation of AMPA receptors was not associated with production of intracellular peroxides, a moderate increase in superoxide production was observed upon exposure to antimycin A (AA). Furthermore, increased activity of Mn- superoxide dismutase (SOD) was observed on selective activation of non-desensitizing AMPA receptors. Taken together, these data make important contributions to the elucidation of the downstream pathways activated in AMPA receptor-mediated excitotoxicity in cultured rat hippocampal neurones.     

Myosin V motor proteins: marching stepwise towards a mechanism

Mammalian myosin V motors transport cargo processively along actin filaments. Recent biophysical and structural studies have led to a detailed understanding of the mechanism of myosin V, making it perhaps the best understood cytoskeletal motor. In addition to describing the mechanism, this review will illustrate how "dynamic" single molecule measurements can synergize with "static" protein structural studies to produce amazingly clear information on the workings of a nanometer-scale machine.     

The spatial organization of centromeric heterochromatin during normal human lymphopoiesis: evidence for ontogenically determined spatial patterns

It is believed that pericentromeric heterochromatin may play a major role in the epigenetic regulation of gene expression. We have previously shown that centromeres in human peripheral blood cells aggregate into distinct "myeloid" and "lymphoid" spatial patterns, suggesting that the three-dimensional organization of centromeric heterochromatin in interphase may be ontogenically determined during hematopoietic differentiation. To investigate this possibility, the spatial patterns of association of different centromeres were analyzed in hematopoietic progenitors and compared with those in early-B and early-T cells, mature B and T lymphocytes, and, additionally, mature granulocytes and monocytes. We show that those patterns change during lymphoid differentiation, with major spatial arrangements taking place at different stages during T and B cell differentiation. Heritable patterns of centromere association are observed, which can occur either at the level of the common lymphoid progenitor, or in early-T or early-B committed cells. A correlation of the observed patterns of centromere association with the gene content of the respective chromosomes further suggests that the variation in the composition of these heterochromatic structures may contribute to the dynamic relocation of genes in different nuclear compartments during cell differentiation, which might have functional implications for cell-stage-specific gene expression.     

Rubritepida flocculans gen. nov., sp. nov., a new slightly thermophilic member of the alpha-1 subclass of the Proteobacteria

A bacterial isolate, with an optimum growth temperature of about 50 degrees C, was recovered from the hot spring at Egerszalók in Hungary. Phylogenetic analyses using the 16S rRNA gene sequence of strain H-8T indicated that the new organism represented a new genus and species of alpha-1 subclass of the Proteobacteria. The major fatty acids of strain H-8T are 16:0, 18:1 omega7c; the rare fatty acid 19:0 20H cyclo 11,12 is also present. Ubiquinone 9 is the major respiratory quinone, the polar lipids are phosphatidylcholine, phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol in addition to two unidentified aminolipids. The new isolate forms red-colored colonies, flocculates in liquid media, is heterotrophic and strictly aerobic. Thiosulfate is oxidized to sulfate, but an increase in biomass could not be measured because of the flocculating behavior. Bacteriochloropyll a was detected by direct spectrophotometric analysis when the organism was grown at 30 degrees C, but could not be detected after growth at 50 degrees C. pufL and pufM genes were present. Heterotrophic growth of strain H-8T occurs on a few carbohydrates, amino acids and organic acids. On the basis of the phylogenetic analyses, physiological and biochemical characteristics, we propose that strain H-8T represents a new genus and a new species most closely related to Roseococcus thiosulfatophilus for which we propose the name Rubritepida flocculans.     

Isolation of viable Toxoplasma gondii from naturally infected aborted bovine fetuses

Neospora caninum and Toxoplasma gondii are related parasites. The former is a common cause of abortion in dairy cattle. The latter has not been conclusively demonstrated in bovine fetuses. During the course of attempts to isolate N. caninum from aborted fetuses, T. gondii was isolated from 2 aborted fetuses, 1 from Portugal and 1 from the United States. Both isolates were made by bioassay of fetal brains in mice. The fetus from Portugal was about 5 mo in gestational age, and the fetus from the United States was a full-term stillborn.     

Mycobacterial infection in farmed turbot Scophthalmus maximus

Mycobacteriosis (piscine tuberculosis) has been reported to affect a wide range of freshwater and marine fish species; however, this is the first report describing mycobacterial infections in turbot Scophthalmus maximus. High numbers of granulomas were initially observed in the organs of moribund farmed turbot. Bacteriological analysis of organs with granulomas led to the isolation of Mycobacterium marinum. Further analysis, to determine the prevalence of the infection in the farm and to identify its source, showed the occurrence of a dual infection by M. marinum and M. chelonae. The presence of Nocardia sp. in some of the fish infected with mycobacteria was also detected. The presence of granulomas in internal organs of apparently healthy fish indicated a high prevalence of the disease, a conclusion that was supported by isolating mycobacteria from all fish with or without granulomas. The infection was probably responsible for the mortality observed (approximately 2% mo(-1)), as most of the recently dead fish presented high numbers of granulomas and isolation of mycobacteria was possible from all of the fish. The isolation of M. marinum from the inlet water suggested this as the most plausible source for the infection occurring in the farm.