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211.
Copper(II)-induced secondary structure changes and reduced folding stability of the prion protein 总被引:1,自引:0,他引:1
Younan ND Klewpatinond M Davies P Ruban AV Brown DR Viles JH 《Journal of molecular biology》2011,410(3):369-382
The cellular isoform of the prion protein PrPC is a Cu2+-binding cell surface glycoprotein that, when misfolded, is responsible for a range of transmissible spongiform encephalopathies. As changes in PrPC conformation are intimately linked with disease pathogenesis, the effect of Cu2+ ions on the structure and stability of the protein has been investigated. Urea unfolding studies indicate that Cu2+ ions destabilise the native fold of PrPC. The midpoint of the unfolding transition is reduced by 0.73 ± 0.07 M urea in the presence of 1 mol equiv of Cu2+. This equates to an appreciable difference in free energy of unfolding (2.02 ± 0.05 kJ mol− 1 at the midpoint of unfolding). We relate Cu2+-induced changes in secondary structure for full-length PrP(23-231) to smaller Cu2+ binding fragments. In particular, Cu2+-induced structural changes can directly be attributed to Cu2+ binding to the octarepeat region of PrPC. Furthermore, a β-sheet-like transition that is observed when Cu ions are bound to the amyloidogenic fragment of PrP (residues 90-126) is due only to local Cu2+ coordination to the individual binding sites centred at His95 and His110. Cu2+ binding does not directly generate a β-sheet conformation within PrPC; however, Cu2+ ions do destabilise the native fold of PrPC and may make the transition to a misfolded state more favourable. 相似文献
212.
David Stroebel Véronique Sendra Kerstin Helbig Jacques Covès 《生物化学与生物物理学报:生物膜》2007,1768(6):1567-1573
We have used analytical ultracentrifugation to explore the oligomeric states of AcrB and CusA in micellar solution of detergent. These two proteins belong to the resistance, nodulation and cell division (RND) family of efflux proteins that are involved in multiple drug and heavy metal resistance. Only the structure of AcrB has been determined so far. Although functional RND proteins should assemble as trimers as AcrB does, both AcrB and CusA form a mixture of quaternary structures (from monomer to heavy oligomer) in detergent solution. The distribution of the oligomeric states was studied as a function of different parameters: nature and concentration of the detergent, ionic strength, pH, protein concentration. This pseudo-heterogeneity does not hamper the crystallization of AcrB as a homotrimer. 相似文献
213.
Mutsuo Ichinomiya Masaki Honda Haruto Shimoda Kenji Saito Tsuneo Odate Mitsuo Fukuchi Akira Taniguchi 《Polar Biology》2007,30(10):1285-1293
Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-,
nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern
Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic
dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates
and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic
dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates
suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered
areas in coastal Antarctic regions are not short but complex. 相似文献
214.
Several fast-transported proteins that appear as single bands after sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolve into multiple spots during isoelectric focusing. A method was devised for determining if such microheterogeneity in net charge indicates that individual polypeptides have been posttranslationally modified to differing extents. Dorsal root ganglia were pulse-labeled with [35S]methionine and either [3H]leucine or [3H]proline, proteins fast-transported into peripheral sensory axons were separated by two-dimensional gel electrophoresis, and isotope incorporation ratios of proteins associated with individual gel spots were determined. When four microheterogeneous glycoproteins were analyzed, each protein "family" showed markedly similar isotope ratios for its three to seven characteristic spots. Such ratios differed between families by almost twofold. In addition, a group of nonglycosylated, sulfate-containing proteins was identified as a family on the basis of the similar isotope incorporation ratios of its component spots. These results suggest that protein microheterogeneity can result from variable sulfation of tyrosine residues as well as from variation in sialic acid-containing oligosaccharide side-chains. More generally, the method can be utilized to test for protein microheterogeneity in cases where the amounts of protein are too low to permit peptide mapping analysis and where the nature of the charge-altering modification is unknown. 相似文献
215.
Zalamea PC Munoz F Stevenson PR Paine CE Sarmiento C Sabatier D Heuret P 《Proceedings. Biological sciences / The Royal Society》2011,278(1717):2437-2445
Plant phenology is concerned with the timing of recurring biological events. Though phenology has traditionally been studied using intensive surveys of a local flora, results from such surveys are difficult to generalize to broader spatial scales. In this study, contrastingly, we assembled a continental-scale dataset of herbarium specimens for the emblematic genus of Neotropical pioneer trees, Cecropia, and applied Fourier spectral and cospectral analyses to investigate the reproductive phenology of 35 species. We detected significant annual, sub-annual and continuous patterns, and discuss the variation in patterns within and among climatic regions. Although previous studies have suggested that pioneer species generally produce flowers continually throughout the year, we found that at least one third of Cecropia species are characterized by clear annual flowering behaviour. We further investigated the relationships between phenology and climate seasonality, showing strong associations between phenology and seasonal variations in precipitation and temperature. We also verified our results against field survey data gathered from the literature. Our findings indicate that herbarium material is a reliable resource for use in the investigation of large-scale patterns in plant phenology, offering a promising complement to local intensive field studies. 相似文献
216.
Yuki Takegawa Makoto Nakamura Shin Nakamura Takumi Noguchi Julien Sellés A. William Rutherford Alain Boussac Miwa Sugiura 《BBA》2019,1860(4):297-309
The monomeric chlorophyll, ChlD1, which is located between the PD1PD2 chlorophyll pair and the pheophytin, PheoD1, is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg2+ is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques. The Mn4CaO5 cluster in the water-splitting site is fully active in both mutants. Changes in thermoluminescence indicate that i) radiative recombination occurs via the repopulation of *ChlD1 itself; ii) non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii) the properties of PD1PD2 were unaffected by this mutation, and consequently iv) the immediate precursor state of the radiative excited state is the ChlD1+PheoD1? radical pair. Chlorophyll bleaching due to high intensity illumination correlated with the amount of 1O2 generated. Comparison of the bleaching spectra with the electrochromic shifts attributed to ChlD1 upon QA? formation, indicates that in the T179H-PSII and in the WT*3-PSII, the ChlD1 itself is the chlorophyll that is first damaged by 1O2, whereas in the T179V-PSII a more red chlorophyll is damaged, the identity of which is discussed. Thus, ChlD1 appears to be one of the primary damage site in recombination-mediated photoinhibition. Finally, changes in the absorption of ChlD1 very likely contribute to the well-known electrochromic shifts observed at ~430?nm during the S-state cycle. 相似文献
217.
218.
Linhua Jiang Rouven Bingel-Erlenmeyer Philipp Korber Daniël C. de Geus Jan Pieter Abrahams 《Journal of molecular biology》2009,386(5):1357-1367
When heat shock prematurely dissociates a translating bacterial ribosome, its 50S subunit is prevented from reinitiating protein synthesis by tRNA covalently linked to the unfinished protein chain that remains threaded through the exit tunnel. Hsp15, a highly upregulated bacterial heat shock protein, reactivates such dead-end complexes. Here, we show with cryo-electron microscopy reconstructions and functional assays that Hsp15 translocates the tRNA moiety from the A site to the P site of stalled 50S subunits. By stabilizing the tRNA in the P site, Hsp15 indirectly frees up the A site, allowing a release factor to land there and cleave off the tRNA. Such a release factor must be stop codon independent, suggesting a possible role for a poorly characterized class of putative release factors that are upregulated by cellular stress, lack a codon recognition domain and are conserved in eukaryotes. 相似文献
219.
Silvia A. Synowsky 《Journal of molecular biology》2009,385(4):1300-8262
Here we combined tandem affinity purification with several mass-spectrometry-based approaches to gain more insight into the composition and structure of the yeast nuclear-cytoplasmic exosome protein complex. The yeast exosome fulfills several different functions in RNA metabolism and can be localized in both the cytoplasm and the nucleus. These two exosome complexes differ in protein composition, although they share several constituents. We focused on these differences in composition by selecting a nuclear-specific exosome protein (Rrp6) and a cytoplasmic-specific protein (Ski7) as the tandem-affinity-purification-tagged affinity bait protein. First, we investigated both these purified exosome assemblies by macromolecular mass spectrometry (MS) to determine the stability and mass of the intact protein complexes and to obtain information on composition and core constituents. We used tandem MS on these intact protein complexes to further probe the composition and to obtain insight into the peripheral nature of some of the constituents. Finally, we combine stable isotope labeling with MS to quantitate differences in exosome composition and posttranslational modifications. We identified a few phosphorylation sites that are differentially regulated between the cytoplasmic exosome and the nuclear exosome. From all of these data, we conclude that the yeast nuclear exosome and the cytoplasmic exosome share a common stable core complex, but are decorated with quite a few differing peripheral proteins. We show that the nuclear exosome selectively copurifies with the α/β importin heterodimer, which is known to be involved in the transport of proteins across the nuclear membrane. 相似文献
220.
Augoustinos S. Stephanou Laurie P. Cooper Andrew R. Thomson C. Logan MacKay Alan Cooper 《Journal of molecular biology》2009,391(3):565-1737
The homodimeric Ocr (overcome classical restriction) protein of bacteriophage T7 is a molecular mimic of double-stranded DNA and a highly effective competitive inhibitor of the bacterial type I restriction/modification system. The surface of Ocr is replete with acidic residues that mimic the phosphate backbone of DNA. In addition, Ocr also mimics the overall dimensions of a bent 24-bp DNA molecule. In this study, we attempted to delineate these two mechanisms of DNA mimicry by chemically modifying the negative charges on the Ocr surface. Our analysis reveals that removal of about 46% of the carboxylate groups per Ocr monomer results in an ∼ 50-fold reduction in binding affinity for a methyltransferase from a model type I restriction/modification system. The reduced affinity between Ocr with this degree of modification and the methyltransferase is comparable with the affinity of DNA for the methyltransferase. Additional modification to remove ∼ 86% of the carboxylate groups further reduces its binding affinity, although the modified Ocr still binds to the methyltransferase via a mechanism attributable to the shape mimicry of a bent DNA molecule. Our results show that the electrostatic mimicry of Ocr increases the binding affinity for its target enzyme by up to ∼ 800-fold. 相似文献