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Single Subunit (single + subunit)
Selected AbstractsPurification, characterization, and cDNA cloning of a novel soluble saxitoxin and tetrodotoxin binding protein from plasma of the puffer fish, Fugu pardalisFEBS JOURNAL, Issue 22 2001Mari Yotsu-Yamashita Some species of puffer fish have been reported to possess both of tetrodotoxin and saxitoxin, which share one binding site on sodium channels. We purified a novel soluble glycoprotein that binds to these toxins from plasma of the puffer fish, Fugu pardalis, and named puffer fish saxitoxin and tetrodotoxin binding protein (PSTBP). PSTBP possessed a binding capacity of 10.6 ± 0.97 nmol·mg,1 protein and a Kd of 14.6 ± 0.33 nm for [3H]saxitoxin in equilibrium binding assays. [3H]Saxitoxin (10 nm) binding to PSTBPs was half-inhibited by the presence of tetrodotoxin and saxitoxin at 12 µm and 8.5 nm, respectively. From the results of gel filtration chromatography (200 kDa) and SDS/PAGE (104 kDa), PSTBP was suggested to consist of noncovalently linked dimers of a single subunit. PSTBP was completely deglycosylated by glycopeptidase F, producing a single band at 42 kDa. Two highly homologous cDNAs to each other coding PSTBP (PSTBP1 and PSTBP2, the predicted amino-acid identity 93%), were obtained from a cDNA library of F. pardalis liver. These proteins consisted to two tandemly repeated homologous domains. The predicted amino-acid sequences of PSTBP1 and 2 were not homologous to that of saxiphilin, a reported saxitoxin binding protein, or sodium channels, but their N-terminus sequences were homologous to that of the reported tetrodotoxin binding protein from plasma of Fugu niphobles, which has not been fully characterized. The partially homologous cDNA sequences to PSTBP1 and 2 were also found in expressed sequence tag clones of nontoxic flounders liver. Presumably, PSTBP is involved in accumulation and/or excretion of toxins in puffer fish. [source] An approach to characterizing single-subunit mutations in multimeric prepores and pores of anthrax protective antigenPROTEIN SCIENCE, Issue 2 2009Blythe E. Janowiak Abstract Heptameric pores formed by the protective antigen (PA) moiety of anthrax toxin translocate the intracellular effector moieties of the toxin across the endosomal membrane to the cytosol of mammalian cells. We devised a protocol to characterize the effects of individual mutations in a single subunit of heptameric PA prepores (pore precursors) or pores. We prepared monomeric PA containing a test mutation plus an innocuous Cys-replacement mutation at a second residue (Lys563, located on the external surface of the prepore). The introduced Cys was biotinylated, and the protein was allowed to cooligomerize with a 20-fold excess of wild-type PA. Finally, biotinylated prepores were freed from wild-type prepores by avidin affinity chromatography. For the proof of principle, we examined single-subunit mutations of Asp425 and Phe427, two residues where Ala replacements have been shown to cause strong inhibitory effects. The single-subunit D425A mutation inhibited pore formation by >104 and abrogated activity of PA almost completely in our standard cytotoxicity assay. The single-subunit F427A mutation caused ,100-fold inhibition in the cytotoxicity assay, and this effect was shown to result from a combination of strong inhibition of translocation and smaller effects on pore formation and ligand affinity. Our results show definitively that replacing a single residue in one subunit of the heptameric PA prepore can inhibit the transport activity of the oligomer almost completely,and by different mechanisms, depending on the specific residue mutated. [source] Determining the topology of virus assembly intermediates using ion mobility spectrometry,mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2010Tom W. Knapman We have combined ion mobility spectrometry,mass spectrometry with tandem mass spectrometry to characterise large, non-covalently bound macromolecular complexes in terms of mass, shape (cross-sectional area) and stability (dissociation) in a single experiment. The results indicate that the quaternary architecture of a complex influences its residual shape following removal of a single subunit by collision-induced dissociation tandem mass spectrometry. Complexes whose subunits are bound to several neighbouring subunits to create a ring-like three-dimensional (3D) architecture undergo significant collapse upon dissociation. In contrast, subunits which have only a single neighbouring subunit within a complex retain much of their original shape upon complex dissociation. Specifically, we have determined the architecture of two transient, on-pathway intermediates observed during in vitro viral capsid assembly. Knowledge of the mass, stoichiometry and cross-sectional area of each viral assembly intermediate allowed us to model a range of potential structures based on the known X-ray structure of the coat protein building blocks. Comparing the cross-sectional areas of these potential architectures before and after dissociation provided tangible evidence for the assignment of the topologies of the complexes, which have been found to encompass both the 3-fold and the 5-fold symmetry axes of the final icosahedral viral shell. Such insights provide unique information about virus assembly pathways that could allow the design of anti-viral therapeutics directed at the assembly step. This methodology can be readily applied to the structural characterisation of many other non-covalently bound macromolecular complexes and their assembly pathways. Copyright © 2010 John Wiley & Sons, Ltd. [source] Stoichiometry of a pore mutation that abolishes picrotoxin-mediated antagonism of the GABAA receptorTHE JOURNAL OF PHYSIOLOGY, Issue 2 2006Anna Sedelnikova Picrotoxin, a potent antagonist of the inhibitory central nervous system GABAA and glycine receptors, is believed to interact with residues that line the central ion pore. These pore-lining residues are in the second transmembrane domain (TM2) of each of the five constituent subunits. One of these amino acids, a threonine at the 6, location, when mutated to phenylalanine, abolishes picrotoxin sensitivity. It has been suggested that this threonine, via hydrogen bonding, directly interacts with the picrotoxin molecule. We previously demonstrated that this mutation, in the ,, , or , subunit, can impart picrotoxin resistance to the GABA receptor. Since the functional pentameric GABA receptor contains two , subunits, two , subunits and one , subunit, it is not clear how many , and , subunits must carry this mutation to impart the resistant phenotype. In this study, by coexpression of mutant , or , subunits with their wild-type counterparts in various defined ratios, we demonstrate that any single subunit carrying the 6, mutation imparts picrotoxin resistance. Implications of this finding in terms of the mechanism of antagonism are considered. [source] Structural studies of wheat flour glutenin polymers by CD spectroscopyBIOPOLYMERS, Issue 4 2004S. Fisichella Abstract A dissolution procedure of unreduced glutenin polymers of three wheat flour varieties (WRU 6981, Alisei 1, and Alisei 2) by sonication in the presence of SDS (sodium dodecyl sulphate), after the elimination of albumins, globulins, and gliadins, was achieved, and the molecular weight distribution of glutenin polymers obtained by this method was measured by matrix assisted laser desorption ionization,time of flight (MALDI-TOF) mass spectrometry. A structural study by CD spectroscopy at different temperatures of WRU 6981 glutenin polymer and of 1Ax1 high- Mr (relative molecular mass) glutenin subunit, which is the only high- Mr subunit contained in WRU 6981 flour, was undertaken to understand if the information obtained from the single subunit were applicable to the total polymer. CD spectroscopy also has been employed to study the glutenin polymers obtained by Alisei 1 and Alisei 2 wheat flours; Alisei 1 biotype contained 1Bx7 and 1Dx2+1Dy12 high-Mr subunits, whereas the Alisei 2 biotype contained only 1Bx7 and 1Dy12 subunits. A conformational study was undertaken by CD spectroscopy at different temperatures and in the presence of some chemical denaturant agents, such as urea and sodium dodecyl sulphate, in order to obtain information about their intrinsic stability and to verify if the 1Dx2 subunit presence determined a different structural behavior between Alisei 1 and Alisei 2 polymers. MALDI-TOF mass spectrometric experiments showed that the glutenin polymers molecular weights were in the mass range of 500,000,5,000,000. CD spectra indicated that a single conformational state did not predominate in the temperature range studied but equilibrium between two distinct conformational states existed; moreover, all the changes induced by urea and by SDS followed a multistep transition process. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source] Characterization of phycoviolobilin phycoerythrocyanin-,84-cystein-lyase-(isomerizing) from Mastigocladus laminosusFEBS JOURNAL, Issue 18 2002Kai-Hong Zhao Cofactor requirements and enzyme kinetics have been studied of the novel, dual-action enzyme, the isomerizing phycoviolobilin phycoerythrocyanin-,84-cystein-lyase(PVB-PEC-lyase) from Mastigocladus laminosus, which catalyses both the covalent attachment of phycocyanobilin to PecA, the apo-,-subunit of phycoerythrocyanin, and its isomerization to phycoviolobilin. Thiols and the divalent metals, Mg2+ or Mn2+, were required, and the reaction was aided by the detergent, Triton X-100. Phosphate buffer inhibits precipitation of the proteins present in the reconstitution mixture, but at the same time binds the required metal. Kinetic constants were obtained for both substrates, the chromophore (Km = 12,16 µm, depending on [PecA], kcat , 1.2 × 10,4·s,1) and the apoprotein (Km = 2.4 µm at 14 µm PCB, kcat = 0.8 × 10,4·s,1). The kinetic analysis indicated that the reconstitution reaction proceeds by a sequential mechanism. By a combination of untagged and His-tagged subunits, evidence was obtained for a complex formation between PecE and PecF (subunits of PVB-PEC-lyase), and by experiments with single subunits for the prevalent function of PecE in binding and PecF in isomerizing the chromophore. [source] Crystallization and preliminary X-ray diffraction studies of the tetramerization domain derived from the human potassium channel Kv1.3ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2009Andreas Winklmeier The tetramerization domain (T1 domain) derived from the voltage-dependent potassium channel Kv1.3 of Homo sapiens was recombinantly expressed in Escherichia coli and purified. The crystals were first grown in an NMR tube in 150,mM potassium phosphate pH 6.5 in the absence of additional precipitants. The crystals showed I4 symmetry characteristic of the naturally occurring tetrameric assembly of the single subunits. A complete native data set was collected to 1.2,Å resolution at 100,K using synchrotron radiation. [source] | ||||||||||