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排序方式: 共有563条查询结果,搜索用时 15 毫秒
1.
Harish Kumar Jayant B. Udgaonkar 《Protein science : a publication of the Protein Society》2021,30(4):785
Amyloid fibrillar aggregates isolated from the brains of patients with neurodegenerative diseases invariably have post‐translational modifications (PTMs). The roles that PTMs play in modulating the structures and polymorphism of amyloid aggregates, and hence their ability to catalyze the conversion of monomeric protein to their fibrillar structure is, however, poorly understood. This is particularly true in the case of tau aggregates, where specific folds of fibrillar tau have been implicated in specific tauopathies. Several PTMs, including acetylation at Lys 280, increase aggregation of tau in the brain, and increase neurodegeneration. In this study, tau‐K18 K280Q, in which the Lys 280 → Gln mutation is used to mimic acetylation at Lys 280, is shown, using HX‐MS measurements, to form fibrils with a structural core that is longer than that of tau‐K18 fibrils. Measurements of critical concentrations show that the binding affinity of monomeric tau‐K18 for its fibrillar counterpart is only marginally more than that of monomeric tau‐K18 K280Q for its fibrillar counterpart. Quantitative analysis of the kinetics of seeded aggregation, using a simple Michaelis–Menten‐like model, in which the monomer first binds and then undergoes conformational conversion to β‐strand, shows that the fibrils of tau‐K18 K280Q convert monomeric protein more slowly than do fibrils of tau‐K18. In contrast, monomeric tau‐K18 K280Q is converted faster to fibrils than is monomeric tau‐K18. Thus, the effect of Lys 280 acetylation on tau aggregate propagation in brain cells is expected to depend on the amount of acetylated tau present, and on whether the propagating seed is acetylated at Lys 280 or not. 相似文献
2.
Cecilia PC Soh Alastair SR Donald James Feeney Walter TJ Morgan Winifred M Watkins 《Glycoconjugate journal》1989,6(3):319-332
The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and1H-500 MHz NMR spectroscopy. In Sda serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity. 相似文献
3.
The incubation of sciatic nerve slices in Krebs Ringer bicarbonate (KRB) buffer (pH 7.4) at 37°C, or the incubation of freshly isolated myelin in ammonium bicarbonate buffer (pH 8), resulted in the generation of a 24kDa protein with a concomitant decrease of PO protein. The conversion of PO into 24kDa protein was blocked by heating isolated myelin at 100°C for 5 min suggesting that the reaction is enzyme mediated. Inclusion of the protease inhibitors and chelating agent to isolated myelin did not prevent the formation of 24kDa protein. Similarly, addition of CaCl2 to isolated myelin did not accentuate the formation of 24kDa protein suggesting that the conversion of PO into 24kDa protein may not be due to Ca2+ activated protease. It is postulated that the formation of 24kDa protein may be due to neutral protease and/or metalloproteinase associated with the PNS myelin. 24kDa protein was purified and characterized. The N-terminal sequence of 1–17 amino acid residues of 24kDa protein was identical to PO. 24kDa protein was immunostained and immunoprecipitated with anti-PO antiserum indicating the immunological similarities between PO and 24kDa protein. Labeling of 24kDa protein with [35S]methionine provided evidence that PO may be in all probability cleaved between Met-168 and Met-193. Further studies were carried out to demonstrate that 24kDa protein was phosphorylated, glycosylated and acylated like PO. Phosphorylation of 24kDa protein in the nerve slices was increased five-fold by phorbol esters and phosphoserine was the only phosphoamino acid identified after partial acid hydrolysis of 24kDa protein. These results suggested that serine residue phosphorylated by protein kinase C may be located in amino acid residues 1-168. 24kDa protein was stained with periodic Schiff reagent. In addition, 24kDa protein was fucosylated and the fucosylation of 24kDa protein was inhibited (70%) by tunicamycin, providing evidence that it is N-glycosylated. Recently, it was demonstrated that both PO and 24kDa protein were fatty acylated with [3H]palmitic acid in the nerve slices and fatty acids are covalently linked to these proteins (Agrawal, H.C. and Agrawal, D. 1989, Biochem. J. 263:173–177). The time course of inhibition of acylation by cycloheximide of 24kDa protein was identical to PO. Cycloheximide inhibited acylation of PO and 24kDa protein by 61% and 58% respectively, whereas, monensin had little affect on the fatty acylation of these proteins. Less [3H]palmitic acid and14C-amino acids were incorporated into 24kDa protein when compared to PO between 5–30 min after incubation of the nerve slices. However, more radioactivity was incorporated into 24kDa protein after 60 min when compared to PO under identical conditions. These results provided evidence of a precursor-product relationship between PO and 24kDa protein. Therefore, PO may be cleaved into 24kDa protein in the myelin membrane following its acylation and glycosylation in the Schwann cells. 相似文献
4.
Two new monosexual and one bisexual species Pratylenchus Filipjev, 1936 collected from Haryana state of India are described and illustrated. The primary distinguishing features of these species are Pratylenchus microstylus n. sp.: L = 331-458 μm, spear = 11 or 12 μm; Pratylenchus cruciferus n. sp.: L = 648-793 μm, central core of lateral fields with oblique lines, hemizonid 2-8 annules anterior to excretory pore; Pratylenchus ekrami n. sp.: spear = 11-13 μm, spermatheca oblong, post vulval uterine sac with differentiated cells, tail with 26-40 annules, males abundant. Studies on intraspecific variations of P. cruciferus, P. ekrami, and P. coffeae (Zimmermann, 1898) Goodey, 1951 revealed that spear length and value of ''V'' are the least variable characters. Body length and size of post vulval uterine sac varies to varying degrees in different species. Shape of median bulb in P. ekrami, number of incisures in P. coffeae, and tail shape in P. ekrami and P. coffeae exhibit the greatest amount of intraspecific variations. P. zeae Graham, 1936 and P. thornei Sher & Allen, 1953 are the other species collected during the present studies. 相似文献
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7.
Isha Gupta Devender Singh Sitender Singh Pawan Kumar Shri Bhagwan Vinod Kumar Harish Kumar Sunil Kumar Chhikara 《Luminescence》2023,38(5):585-599
Terbium(III)-doped yttrium aluminate perovskite (YAP:xTb3+) (x = 0.01–0.08 mol) was synthesized using a simple gel-combustion method. Structural elucidations were performed using X-ray diffraction (XRD) and Rietveld analysis. Fourier-transform infrared spectral studies validated the efficient synthesis of designed doped samples. Transmission electron microscopic images showed the agglomerated irregular dimensions of the synthesized nanocrystalline materials. When excited at 251 nm, a strong emissive line attributed to 5D4 → 7F5 electronic transition was observed at 545 nm (green emission). The maximum luminescence was found at the optimized concentration (0.05 mol) of Tb3+ ions; this emission was quenched by dipolar–dipolar (d–d) interactions. Chromaticity (x and y) and correlated colour temperature parameters were obtained by analysing the emission profiles. Finally, the colour coordinates of nanophosphors were closer to the National Television Standards Committee green coordinates, which replicates their potency in the design and architecture of R-G-B-based white LEDs. 相似文献
8.
Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata 总被引:2,自引:0,他引:2
R LATHA C SRINIVAS RAO H M SR SUBRAMANIAM P EGANATHAN M S SWAMINATHAN 《The Annals of applied biology》2004,144(2):177-184
Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice. 相似文献
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10.
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献