Search results for "Quaternary"
showing 10 items of 411 documents
Mutations in the Bacillus thuringiensis Cry1Ca toxin demonstrate the role of domains II and III in specificity towards Spodoptera exigua larvae
2004
Several mutants of the Bacillus thuringiensis Cry1Ca toxin affected with regard to specific activity towards Spodoptera exigua were studied. Alanine was used to replace single residues in loops 2 and 3 of domain II (mutant pPB19) and to replace residues 541– 544 in domain III (mutant pPB20). Additionally, a Cry1Ca mutant combining all mutations was constructed (mutant pPB21). Toxicity assays showed a marked decrease in toxicity against S. exigua for all mutants, while they retained their activity against Manduca sexta, confirming the importance of these residues in determining insect specificity. Parameters for binding to the specific receptors in BBMV (brush border membrane vesicles) of S.…
A linear Fe-O-Fe unit in bis(dibenzyldimethylammonium) mu-oxo-bis[tribromoferrate(III)].
2006
The title compound, (C 16 H 20 )N) 2 [Fe 2 Br 6 O], crystallizes with one dibenzyldimethylammonium cation and one half of a μ-oxo-bis[tribromoferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe-O-Fe unit. The iron(III) cations have tetrahedral geometry, with bond angles in the range 106.8 (1)-112.2 (1)°. The ion pairs are held together by Coulombic forces and C-H···Br hydrogen bonds. Each Br - anion forms one hydrogen bond. No C-H···O hydrogen bonds are found between the O atom in the Fe-O-Fe unit and surrounding counter-cations, consistent with the linear configuration of the Fe-O-Fe unit.
Quaternary structure of the European spiny lobster (Palinurus elephas) 1x6-mer hemocyanin from cryoEM and amino acid sequence data.
2002
Abstract Arthropod hemocyanins are large respiratory proteins that are composed of up to 48 subunits (8×6-mer) in the 75 kDa range. A 3D reconstruction of the 1×6-mer hemocyanin from the European spiny lobster Palinurus elephas has been performed from 9970 single particles using cryoelectron microscopy. An 8 A resolution of the hemocyanin 3D reconstruction has been obtained from about 600 final class averages. Visualisation of structural elements such as α-helices has been achieved. An amino acid sequence alignment shows the high sequence identity (>80%) of the hemocyanin subunits from the European spiny lobster P. elephas and the American spiny lobster Panulirus interruptus . Comparison of…
Strombine dehydrogenase in the demosponge Suberites domuncula: Characterization and kinetic properties of the enzyme crucial for anaerobic metabolism
2008
Previously, the cDNA and the respective gene for a presumed tauropine dehydrogenase (TaDH) from Suberites domuncula (GenBank accession nos. AM712888, AM712889) had been annotated. The conclusion that the sequences encode a TaDH had been inferred from the 68% identity with the TaDH protein from the marine demosponge Halichondria japonica. However, subsequent enzymatic assays shown here indicate that the presumed S. domuncula opine dehydrogenase is in fact a strombine dehydrogenase (StDH). The enzyme StDH is highly specific for glycine and is inhibited by an excess of the substrate pyruvate. Besides kinetic data, we report in this study also on the predicted tertiary and quaternary structure …
Pore formation by Vibrio cholerae cytolysin follows the same archetypical mode as beta-barrel toxins from gram-positive organisms.
2009
Vibrio cholerae cytolysin (VCC) forms SDS-stable heptameric beta-barrel transmembrane pores in mammalian cell membranes. In contrast to structurally related pore formers of gram-positive organisms, no oligomeric prepore stage of assembly has been detected to date. In the present study, disulfide bonds were engineered to tie the pore-forming amino acid sequence to adjacent domains. In their nonreduced form, mutants were able to bind to rabbit erythrocytes and to native erythrocyte membranes suspended in PBS solution and form SDS-labile oligomers. These remained nonfunctional and represented the long-sought VCC prepores. Disulfide bond reduction in these oligomers released the pore-forming se…
Structure of Mega-Hemocyanin Reveals Protein Origami in Snails
2014
SummaryMega-hemocyanin is a 13.5 MDa oxygen transporter found in the hemolymph of some snails. Similar to typical gastropod hemocyanins, it is composed of 400 kDa building blocks but has additional 550 kDa subunits. Together, they form a large, completely filled cylinder. The structural basis for this highly complex protein packing is not known so far. Here, we report the electron cryomicroscopy (cryo-EM) structure of mega-hemocyanin complexes from two different snail species. The structures reveal that mega-hemocyanin is composed of flexible building blocks that differ in their conformation, but not in their primary structure. Like a protein origami, these flexible blocks are optimally pac…
The structure of Yersinia pestis Caf1 polymer in free and adjuvant bound states
2010
Caf1 of the plague bacterium, Yersinia pestis is a polymeric virulence factor and vaccine component, formed from monomers by a donor strand exchange (DSE) mechanism. Here, EM images of Caf1 reveal flexible polymers up to 1.5 microm long (4MDa). The bead-like structures along the polymer are 5.8 + or - 1 nm long and correspond to single Caf1 proteins. Short polymers often form circles, presumably by DSE. We also provide the first images of proteins bound to alhydrogel adjuvant. Caf1, hemocyanin and anthrax PA are all resolved clearly and Caf1 exhibits adjuvant bound stretches with long intervening loops draped from the edges.
Canonical azimuthal rotations and flanking residues constrain the orientation of transmembrane helices.
2013
AbstractIn biological membranes the alignment of embedded proteins provides crucial structural information. The transmembrane (TM) parts have well-defined secondary structures, in most cases α-helices and their orientation is given by a tilt angle and an azimuthal rotation angle around the main axis. The tilt angle is readily visualized and has been found to be functionally relevant. However, there exist no general concepts on the corresponding azimuthal rotation. Here, we show that TM helices prefer discrete rotation angles. They arise from a combination of intrinsic properties of the helix geometry plus the influence of the position and type of flanking residues at both ends of the hydrop…
Structural Characterization of Set1 RNA Recognition Motifs and their Role in Histone H3 Lysine 4 Methylation
2006
Departament de Bioquimica iBiologia Molecular, Universitatde Valencia, C/Dr Moliner 50,46100, Burjassot, SpainThe yeast Set1 histone H3 lysine 4 (H3K4) methyltransferase contains, inaddition to its catalytic SET domain, a conserved RNA recognition motif(RRM1). We present here the crystal structure and the secondary structureassignment in solution of the Set1 RRM1. Although RRM1 has the expectedβαββαβ RRM-fold, it lacks the typical RNA-binding features of thesemodules. RRM1 is not able to bind RNA by itself in vitro, but a constructcombining RRM1 with a newly identified downstream RRM2 specificallybinds RNA. Invivo,H3K4 methylation isnot affectedbyapoint mutation inRRM2 that preserves Set1 s…
Crystallization and Preliminary Analysis of Crystals of the 24-Meric Hemocyanin of the Emperor Scorpion (Pandinus imperator)
2011
Hemocyanins are giant oxygen transport proteins found in the hemolymph of several invertebrate phyla. They constitute giant multimeric molecules whose size range up to that of cell organelles such as ribosomes or even small viruses. Oxygen is reversibly bound by hemocyanins at binuclear copper centers. Subunit interactions within the multisubunit hemocyanin complex lead to diverse allosteric effects such as the highest cooperativity for oxygen binding found in nature. Crystal structures of a native hemocyanin oligomer larger than a hexameric substructure have not been published until now. We report for the first time growth and preliminary analysis of crystals of the 24-meric hemocyanin (M(…