Crystal structures, dynamics and functional implications of molybdenum-cofactor biosynthesis protein MogA from two thermophilic organisms

Molybdenum-cofactor (Moco) biosynthesis is an evolutionarily conserved pathway in almost all kingdoms of life, including humans. Two proteins, MogA and MoeA, catalyze the last step of this pathway in bacteria, whereas a single two-domain protein carries out catalysis in eukaryotes. Here, three crystal structures of the Moco-biosynthesis protein MogA from the two thermophilic organisms Thermus thermophilus (TtMogA; 1.64 angstrom resolution, space group P2(1)) and Aquifex aeolicus (AaMogA; 1.70 angstrom resolution, space group P2(1) and 1.90 angstrom resolution, space group P1) have been determined. The functional roles and the residues involved in oligomerization of the protein molecules have been identified based on a comparative analysis of these structures with those of homologous proteins. Furthermore, functional roles have been proposed for the N- and C-terminal residues. In addition, a possible protein-protein complex of MogA and MoeA has been proposed and the residues involved in protein-protein interactions are discussed. Several invariant water molecules and those present at the subunit interfaces have been identified and their possible structural and/or functional roles are described in brief. In addition, molecular-dynamics and docking studies with several small molecules (including the substrate and the product) have been carried out in order to estimate their binding affinities towards AaMogA and TtMogA. The results obtained are further compared with those obtained for homologous eukaryotic proteins.

On the out of phase appearance of large-scale diffuse magnetic field of the sun with respect to sunspots

We assume the large-scale diffuse magnetic field of the Sun to originate from the poloidal component of a dynamo operating at the base of the convection zone, whereas the sunspots are due to the toroidal component. The evolution of the poloidal component is studied to model the poleward migration of the diffuse field seen on the solar surface and the polar reversal at the time of sunspot maxima (Dikpati and Choudhuri 1994, 1995).

Synthesis, properties and crystal structures of diastereomeric areneruthenium(II) chiral Schiff-base complexes

Diastereomers (SRu,Sc)-1a and (RRu,Sc)-1b, in a ratio of 85: 15 and formulated as [Ru(η-MeC6H4Pri-p)Cl(L*)], have been prepared by treating [{Ru(η-MeC6H4Pri-p)Cl2}2] with the sodium salt of (S)-α-methylbenzylsalicylaldimine (HL*) in tetrahydrofuran at –70 °C. The reaction of 1(1a+1b) with AgClO4 in acetone followed by an addition of PPh3 or 4-methylpyridine (4Me-py) leads to the formation of adducts [Ru(η-MeC6H4Pri-p)(PPh3)(L*)]ClO42[(SRu,Sc)2a, (FRu,Sc)2b] and [Ru(η-MeC6H4Pri-p)(4Me-py)(L*)]ClO43[(SRu,Sc)3a, (RRu,Sc)3b] in the diastereomeric ratios (SRu,Sc) : (RRu,Sc) of 2 : 98 and 76 : 24, respectively. Complex 1 crystallises with equal numbers of 1a and 1b molecules in an asymmetric unit of monoclinic space group P21 with a= 10.854(1), b= 17.090(1), c= 12.808(4)Å, β= 110.51(1)°, and Z= 4. The structure was refined to R= 0.0552 and R′= 0.0530 with 2893 reflections having I[gt-or-equal] 1.5σ(I). The absolute configurations of the chiral centres in the optically pure single crystal of the PPh3 adduct have been obtained from an X-ray study. Crystals of formulation [Ru(η-MeC6H4Pri-p)-(PPh3)(L*)]2[ClO4][PF6]·1.5 CHCl3, obtained in presence of both ClO4 and PF6 anions, belong to the non-centric triclinic space group P1 with a= 10.852(2), b= 14.028(1), c= 15.950(2)Å, α= 91.51(1), β= 105.97(1), γ= 106.11(1)°, and Z= 2. The final residuals were R= 0.0713, R′= 0.0752 with 7283 reflections having I[gt-or-equal] 2.5σ(I). The crystal structures of 1a,1b, and the PPh3 adduct (2b,2b′) consist of a ruthenium(II) centre bonded to a η-p-cymene, a bidentate chelating Schiff base, and a unidentate ligand (Cl or PPh3). The chirooptical properties of the complexes have been studied using 1H NMR and CD spectral data. The presence of a low-energy barrier for the intermediate involved in these reactions, showing both retention as well as inversion of the metal configuration, is discussed.

Large deformation finite element analysis of laminated circular composite plates

A 48 d.o.f., four-noded quadrilateral laminated composite shell finite element is particularised to a sector finite element and is used for the large deformation analysis of circular composite laminated plates. The strain-displacement relationships for the sector element are obtained by reducing those of the quadrilateral shell finite element by substituting proper values for the geometric parameters. Subsequently, the linear and tangent stiffness matrices are formulated using conventional methods. The Newton-Raphson method is employed as the nonlinear solution technique. The computer code developed is validated by solving an isotropic case for which results are available in the literature. The method is then applied to solve problems of cylindrically orthotropic circular plates. Some of the results of cylindrically orthotropic case are compared with those available in the literature. Subsequently, application is made to the case of laminated composite circular plates having different lay-up schemes. The computer code can handle symmetric/unsymmetric lay-up schemes. The large displacement analysis is useful in estimating the damage in composite plates caused by low-velocity impact.

Zn(II), Cd(II) and Hg(II) complexes with 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole: Syntheses, structures and luminescence

Five coordination compounds Zn(mbmpbi)(2)Cl-2 (1), Zn(mbmpbi)(2)Br-2 (2), Cd(mbmpbi)(2)Cl-2 (3), Hg(mbmpbi)(2)Cl-2 (4) and Hg(mbmpbi)(2)Br-2 (5) were synthesized by the reaction of 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole (mbmpbi) with the corresponding metal halides. The complexes have been characterized by elemental analysis, conductance measurements, FT-IR, H-1 NMR and photoluminescence spectral studies. The ligand mbmpbi exhibits the N-benzimidazole coordination. The structures of 3-5 have been determined by single crystal X-ray diffraction. These three complexes are isostructural, crystallizing in the monoclinic system. P2/n space group with a distorted tetrahedral geometry around the metal ion. Zn(II) and Cd(II) complexes show strong blue emission in solid state at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.

Homogenization of periodic structures via Bloch decomposition

In this paper, the classical problem of homogenization of elliptic operators in arbitrary domains with periodically oscillating coefficients is considered. Using Bloch wave decomposition, a new proof of convergence is furnished. It sheds new light and offers an alternate way to view the classical results. In a natural way, this method leads us to work in the Fourier space and thus in a framework dual to the one used by L. Tartar [Problemes d'Homogeneisation dans les Equations aux: Derivees Partielles, Cours Peccot au College de Prance, 1977] in his method of homogenization. Further, this technique offers a nontraditional way of calculating the homogenized coefficients which is easy to implement in the computer.

Micellar structures of dimeric surfactants with phosphate head groups and wettable spacers: A small-angle neutron scattering study

Dimeric or gemini surfactants consist of two hydrophobic chains and two hydrophilic head groups covalently connected by a hydrophobic or hydrophilic spacer. This paper reports the small-angle neutron scattering (SANS) measurements from aqueous micellar solutions of two different recently developed types of dimeric surfactants: (i) bis-anionic C16H33PO4--(CH2)(m)-PO4-C16H33,2Na(+) dimeric surfactants composed of phosphate head groups and a hydrophobic polymethylene spacer, referred to as 16-m-16,2Na(+), for spacer lengths m = 2, 4, 6, and 10, (ii) bis-cationic C16H33N+(CH3)(2)-CH2-(CH2-O-CH2)(p)-CH2-N+ (CH3)(2)C16H33,2Br(-) dimeric surfactants composed of dimethylammonium head groups and a wettable polyethylene oxide spacer, referred to as 16-CH2-p-CH2-16,2Br(-), for spacer lengths p = 1 - 3. The micellar structures of these surfactants are compared with the earlier studied bis-cationic C16H33N+ (CH3)(2)-(CH2)(m)-N+ (CH3)(2)C16H33,2Br(-) dimeric surfactants composed of dimethylammonium head groups and a hydrophobic polymethylene spacer, referred to as 16-m-16,2Br(-). It is found that 16-m-16,2Na(+), similar to 16-m-16,2Br(-), form various micellar structures depending on the spacer length. Micelles an disklike for rn = 2, rodlike for m = 4, and prolate ellipsoidal fur m = 6 and 10. The micelles of 16-CH2-p-CH2-16,2Br(-) are prolate ellipsoidal for all the values of p = 1 - 3. It is also found that micelles of 16-m-16,2Na(+) and 16-CH2-p-CH2-16,2Br(-) are large in comparison to those of 16-in-16,2Br(-) for similar spacer lengths. This is connected with the fact that both in 16-m-16,2Na(+) and 16-CH2-p-CH2-16,2Br(-), the head group or the spacer is more hydrated as compared to that in the 16-m-16,2Br(-). An increase in the hydration of the spacer or the head group increases the screening of the Coulomb repulsion between the charged head groups. This effect has been found to be more pronounced in the dimeric surfactants having wettable spacers. [S1063-651X(99)00303-7].

Spectral asymptotics of the Helmholtz model in fluid-solid structures

A model representing the vibrations of a coupled fluid-solid structure is considered. This structure consists of a tube bundle immersed in a slightly compressible fluid. Assuming periodic distribution of tubes, this article describes the asymptotic nature of the vibration frequencies when the number of tubes is large. Our investigation shows that classical homogenization of the problem is not sufficient for this purpose. Indeed, our end result proves that the limit spectrum consists of three parts: the macro-part which comes from homogenization, the micro-part and the boundary layer part. The last two components are new. We describe in detail both macro- and micro-parts using the so-called Bloch wave homogenization method. Copyright (C) 1999 John Wiley & Sons, Ltd.

Structures of the catalytic site mutants D99A and H48Q and the calcium-loop mutant D49E of phospholipase A(2)

Crystal structures of the active-site mutants D99A and H48Q and the calcium-loop mutant D49E of bovine phospholipase A(2) have been determined at around 1.9 Angstrom resolution. The D99A mutant is isomorphous to the orthorhombic recombinant enzyme, space group P2(1)2(1)2(1), The H48Q and the calcium-loop mutant D49E are isomorphous to the trigonal recombinant enzyme, space group P3(1)21, The two active-site mutants show no major structural perturbations. The structural water is absent in D99A and, therefore, the hydrogen-bonding scheme is changed. In H48Q, the catalytic water is present and hydrogen bonded to Gln48 N, but the second water found in native His48 is absent. In the calcium-loop mutant D49E, the two water molecules forming the pentagonal bipyramid around calcium are absent and only one O atom of the Glu49 carboxylate group is coordinated to calcium, resulting in only four ligands.

Improved large-MIMO detection based on damped belief propagation

In this paper, we consider the application of belief propagation (BP) to achieve near-optimal signal detection in large multiple-input multiple-output (MIMO) systems at low complexities. Large-MIMO architectures based on spatial multiplexing (V-BLAST) as well as non-orthogonal space-time block codes(STBC) from cyclic division algebra (CDA) are considered. We adopt graphical models based on Markov random fields (MRF) and factor graphs (FG). In the MRF based approach, we use pairwise compatibility functions although the graphical models of MIMO systems are fully/densely connected. In the FG approach, we employ a Gaussian approximation (GA) of the multi-antenna interference, which significantly reduces the complexity while achieving very good performance for large dimensions. We show that i) both MRF and FG based BP approaches exhibit large-system behavior, where increasingly closer to optimal performance is achieved with increasing number of dimensions, and ii) damping of messages/beliefs significantly improves the bit error performance.

Strip based coding for large images using wavelets

Thanks to advances in sensor technology, today we have many applications (space-borne imaging, medical imaging, etc.) where images of large sizes are generated. Straightforward application of wavelet techniques for above images involves certain difficulties. Embedded coders such as EZW and SPIHT require that the wavelet transform of the full image be buffered for coding. Since the transform coefficients also require storing in high precision, buffering requirements for large images become prohibitively high. In this paper, we first devise a technique for embedded coding of large images using zero trees with reduced memory requirements. A 'strip buffer' capable of holding few lines of wavelet coefficients from all the subbands belonging to the same spatial location is employed. A pipeline architecure for a line implementation of above technique is then proposed. Further, an efficient algorithm to extract an encoded bitstream corresponding to a region of interest in the image has also been developed. Finally, the paper describes a strip based non-embedded coding which uses a single pass algorithm. This is to handle high-input data rates. (C) 2002 Elsevier Science B.V. All rights reserved.

Studies on the effects of test gas on the flow field around large angle blunt cone flying at hypersonic Mach number

The effect of the test gas on the flow field around a 120degrees apex angle blunt cone has been investigated in a shock tunnel at a nominal Mach number of 5.75. The shock standoff distance around the blunt cone was measured by an electrical discharge technique using both carbon dioxide and air as test gases. The forebody laminar convective heat transfer to the blunt cone was measured with platinum thin-film sensors in both air and carbon dioxide environments. An increase of 10 to 15% in the measured heat transfer values was observed with carbon dioxide as the test gas in comparison to air. The measured thickness of the shock layer along the stagnation streamline was 3.57 +/- 0.17 mm in air and 3.29 +/- 0.26 mm in carbon dioxide. The computed thickness of the shock layer for air and carbon dioxide were 3.98 mm and 3.02 mm, respectively. The observed increase in the measured heat transfer rates in carbon dioxide compared to air was due to the higher density ratio across the bow shock wave and the reduced shock layer thickness.

Sulfates of organic diamines: hydrogen-bonded structures and properties

In order to investigate the supramolecular hydrogen-bonded networks and other structural features exhibited by compounds containing an organic cation and an inorganic anion, sulfates of the organic diamines, ethylenediamine (I), 1,3-diaminopropane (II), piperazine (III), and 1,4-diazabicyclo[2.2.2]octane (DABCO) (IV) have been prepared investigated by X-ray crystallography. While II, III, and IV crystallize in the centrosymmetric space group, Pbca, P2(1)/n, Pbcn, respectively, I crystallizes in the non-centrosymmetric space group, P4(1) exhibiting chirality and weak NLO properties. I-IV exhibit different types of supramolecular H-bonded networks involving the organic cation and the SO42- anion. The nature and strength of the H-bonding network vary from one compound to another, with the strongest network found in piperazinium sulfate, III, and the weakest in II. While in III, water molecules form part of the H-bonded network, they are present as guest molecules in the channels of IV. Thermal stability of the compounds as well as the infrared spectra reflect the stabilities of these H-bonded solids. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

A layered chlorophosphate, Na-3[Cd4Cl3(HPO4)(2)(H2PO4)(4)], containing Na+ ions in the interlamellar space

Reaction between CdCl2.H2O and NaH2PO4.H2O Under hydrothermal conditions gives rise to a new cadmium chlorophosphate of the formula Na-3[Cd4Cl3(HPO4)(2)(H2PO4)(4)] I. This material crystallizes in the orthorhombic system with space group Fmm2(no. 42). I has macroanionic layers of [Cd4Cl3(HPO4)(2)(H2PO4)(4)](3-) with Na+ ions in the interlamellar space. The discovery of such compounds suggests that metathetic reactions carried out under hydrothermal conditions may provide a novel route for the synthesis of new open-framework structures.

MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.