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61.
Plus-end tracking proteins, such as EB1 and the dynein/dynactin complex, regulate microtubule dynamics. These proteins are thought to stabilize microtubules by forming a plus-end complex at microtubule growing ends with ill-defined mechanisms. Here we report the crystal structure of two plus-end complex components, the carboxy-terminal dimerization domain of EB1 and the microtubule binding (CAP-Gly) domain of the dynactin subunit p150Glued. Each molecule of the EB1 dimer contains two helices forming a conserved four-helix bundle, while also providing p150Glued binding sites in its flexible tail region. Combining crystallography, NMR, and mutational analyses, our studies reveal the critical interacting elements of both EB1 and p150Glued, whose mutation alters microtubule polymerization activity. Moreover, removal of the key flexible tail from EB1 activates microtubule assembly by EB1 alone, suggesting that the flexible tail negatively regulates EB1 activity. We, therefore, propose that EB1 possesses an auto-inhibited conformation, which is relieved by p150Glued as an allosteric activator. 相似文献
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In the title family, the ONO donor ligands are the acetylhydrazones of salicylaldehyde (H2L1) and 2-hydroxyacetophenone (H2L2) (general abbreviation, H2L). The reaction of bis(acetylacetonato)oxovanadium(IV) with a mixture of tridentate H2L and a bidentate NN donor [e.g., 2,2′-bipyridine(bpy) or 1,10-phenanthroline(phen), hereafter B] ligands in equimolar ratio afforded the tetravalent complexes of the type [VIVO(L)(B)]; complexes (1)-(4) whereas, if B is replaced by 8-hydroxyquinoline(Hhq) (which is a bidentate ON donor ligand), the above reaction mixture yielded the pentavalent complexes of the type [VVO(L)(hq)]; complexes (5) and (6). Aerial oxygen is most likely the oxidant (for the oxidation of VIV → VV) in the synthesis of pentavalent complexes (5) and (6). [VIVO(L)(B)] complexes are one electron paramagnetic and display axial EPR spectra, while the [VVO(L)(hq)] complexes are diamagnetic. The X-ray structure of [VVO(L2)(hq)] (6) indicates that H2L2 ligand is bonded with the vanadium meridionally in a tridentate dinegative fashion through its phenolic-O, enolic-O and imine-N atoms. The general bond length order is: oxo < phenolato < enolato. The V-O (enolato) bond is longer than V-O (phenolato) bond by ∼0.07 Å and is identical with V-O (carboxylate) bond. 1H NMR spectrum of (6) in CDCl3 solution indicates that the binding nature in the solid state is also retained in solution. Complexes (1)-(4) display two ligand-field transitions in the visible region near 820 and 480 nm in DMF solution and exhibit irreversible oxidation peak near +0.60 V versus SCE in DMSO solution, while complexes (5) and (6) exhibit only LMCT band near 535 nm and display quasi-reversible one electron reduction peak near −0.10 V versus SCE in CH2Cl2 solution. The VO3+-VO2+E1/2 values shift considerably to more negative values when neutral NN donor is replaced by anionic ON donor species and it also provides better VO3+ binding via phenolato oxygen. For a given bidentate ligand, E1/2 increases in the order: (L2)2− < (L1)2−. 相似文献
63.
Tapas?K?BasakEmail author Suman?Halder Madona?Kumar Renu?Sharma Bijoylaxmi?Midya 《Theoretical biology & medical modelling》2005,2(1):11
Background
The present paper describes a topological model of biofeedback. This model incorporates input from a sensory organ and a transduction phase mediated through catecholamine production in the feedback path. The transduction phase comprises both conservative and dissipative systems, from which the appropriate output is combined in a closed loop. 相似文献64.
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Joseph Markowitz Tapas K. Mal Chunhua Yuan Nicholas B. Courtney Mitra Patel Andrew R. Stiff James Blachly Christopher Walker Ann‐Kathrin Eisfeld Albert de la Chapelle William E. Carson III 《Protein science : a publication of the Protein Society》2016,25(5):1069-1074
It was recently discovered that the NRAS isoform 5 (20 amino acids) is expressed in melanoma and results in a more aggressive cell phenotype. This novel isoform is responsible for increased phosphorylation of downstream targets such as AKT, MEK, and ERK as well as increased cellular proliferation. This structure report describes the NMR solution structure of NRAS isoform 5 to be used as a starting point to understand its biophysical interactions. The isoform is highly flexible in aqueous solution, but forms a helix‐turn‐coil structure in the presence of trifluoroethanol as determined by NMR and CD spectroscopy. 相似文献
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Tapas Chandra Nag 《Acta zoologica》1994,75(3):209-211
Abstract In the duplex retina of the catfish Clarias batrachus(Linnaeus, 1758), the apical processes of the pigment epithelial cells have been found by transmission electron microscopy to be in intimate contact with the calycal processes around the basal portion of the photoreceptor outer segments. It is hypothesized that the retinal pigment epithelium effectively transports synthesized products and metabolites to the photoreceptor inner segments via the anatomical zone of the apical–calycal processes interface in this species. 相似文献