Synthesis, structure and redox properties of (?-oxo)bis(?-carboxylato)diruthenium(III) complexes containing three different terminal ligands

Blue coloured, unstable, essentially diamagnetic and non-electrolytic diruthenium(III) complexes of the formation [Ru2O(O2CR)4(en)2(PPh3)2] were prepared by reacting [Ru2O(O2CR)4(PPh3)2] with 1,2-diaminoethane (en) in CH2Cl2 (R = C6H4-p-X; X = H, Me and OMe). The molecular structure of the complexes is proposed as [{(?1-O2CR)(?1-en)(PPH3)Ru}2(?-O)(?-O2CR)2] based on the 1H NMR spectral data. The electronic spectra of the complexes display a band near 569 nm with a shoulder at 630 nm. In CH2Cl2-0.1 M [Bun4N]ClO4, the complexes exhibit redox couples Ru2III,III/Ru2III,IV and Ru2III,IV/Ru2IV,IV near 0.1 and 1.2 V (vs SCE), respectively. The potentials are the lowest among diruthenium(III) complexes with a similar core structure.

Interactions of 3' terminal and 5' terminal regions of physalis mottle virus genomic RNA with its replication complex

Physalis mottle virus (PhMV) belongs to the tymogroup of positive-strand RNA viruses with a genome size of 6 kb. Crude membrane preparations from PhMV-infected Nicotiana glutinosa plants catalyzed the synthesis of PhMV genomic RNA from endogenously bound template. Addition of exogenous genomic RNA enhanced the synthesis which was specifically inhibited by the addition of sense and antisense transcripts corresponding to 3' terminal 242 nucleotides as well as the 5' terminal 458 nucleotides of PhMV genomic RNA while yeast tRNA or ribosomal RNA failed to inhibit the synthesis. This specific inhibition suggested that the 5' and 3' non-coding regions of PhMV RNA might play an important role in viral replication.

Synthesis and structure of a novel terminal imido complex of titanium

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Synergy between the N-terminal and C-terminal domains of Mycobacterium tuberculosis HupB is essential for high-affinity binding, DNA supercoiling and inhibition of RecA-promoted strand exchange

The occurrence of DNA architectural proteins containing two functional domains derived from two different architectural proteins is an interesting emerging research theme in the field of nucleoid structure and function. Mycobacterium tuberculosis HupB, unlike Escherichia coli HU, is a two-domain protein that, in the N-terminal region, shows broad sequence homology with bacterial HU. The long C-terminal extension, on the other hand, contains seven PAKK/KAAK motifs, which are characteristic of the histone H1/H5 family of proteins. In this article, we describe several aspects of HupB function, in comparison with its truncated derivatives lacking either the C-terminus or N-terminus. We found that HupB binds a variety of DNA repair and replication intermediates with K(d) values in the nanomolar range. By contrast, the N-terminal fragment of M. tuberculosis HupB (HupB(MtbN)) showed diminished DNA-binding activity, with K(d) values in the micromolar range, and the C-terminal domain was completely devoid of DNA-binding activity. Unlike HupB(MtbN), HupB was able to constrain DNA in negative supercoils and introduce negative superhelical turns into relaxed DNA. Similarly, HupB exerted a robust inhibitory effect on DNA strand exchange promoted by cognate and noncognate RecA proteins, whereas HupB(MtbN), even at a 50-fold molar excess, had no inhibitory effect. Considered together, these results suggest that synergy between the N-terminal and C-terminal domains of HupB is essential for its DNA-binding ability, and to modulate the topological features of DNA, which has implications for processes such as DNA compaction, gene regulation, homologous recombination, and DNA repair.

Sliding-Mode Guidance and Control for All-Aspect Interceptors with Terminal Angle Constraints

In this paper, sliding-mode-control-based guidance laws to intercept stationary, constant-velocity, and maneuvering targets at a desired impact angle are proposed. The desired impact angle, which is defined in terms of a desired line-of-sight angle, is achieved in finite time by selecting the missile's lateral acceleration to enforce terminal sliding mode on a switching surface designed using nonlinear engagement dynamics. The conditions for capturability are also presented. In addition, by considering a three-degree-of-freedom linear-interceptor dynamic model and by following the procedure used to design a dynamic sliding-mode controller, the interceptor autopilot is designed as a simple static controller to track the lateral acceleration generated by the guidance law. Numerical simulation results are presented to validate the proposed guidance laws and the autopilot design for different initial engagement geometries and impact angles.

Theoretical and in vitro studies of a C-terminal peptide from PGKC of Leishmania mexicana mexicana

Trypanosomatids cause deadly diseases in humans. Of the various biochemical pathways in trypanosomatids, glycolysis, has received special attention because of being sequestered in peroxisome like organelles critical for the survival of the parasites. This study focuses on phosphoglycerate kinase (PGK) from Leishmania spp. which, exists in two isoforms, the cytoplasmic PGKB and glycosomal PGKC differing in their biochemical properties. Computational analysis predicted the likelihood of a transmembrane helix only in the glycosomal isoform PGKC, of approximate length 20 residues in the 62-residue extension, ending at, arginine residues R471 and R472. From experimental studies using circular dichroism and NMR with deuterated sodium dodecyl sulfate, we find that the transmembrane helix spans residues 448 +/- 2 to 476 in Leishmania mexicana PGKC. The significance of this observation is discussed in the context of glycosomal transport and substrate tunneling. (C) 2012 Elsevier B.V. All rights reserved.

Estimation of electric stress and surface potential for traction insulators

Traction insulators are solid core insulators widely used for railway electrification. Constant exposure to detrimental effects of vandalism, and mechanical vibrations begets certain faults like shorting of sheds or cracks in the sheds. Due to fault in one/two sheds, stress on the remaining healthy sheds increases, owing to atmospheric pollution the stress may lead to a flashover of the insulator. Presently due to non availability of the electric stress data for the insulators, simulation study is carried out to find the potential and electric field for most widely used traction insulators in the country. The results of potential and electric field stress obtained for normal and faulty imposed insulators are presented.

Distinctive contributions of the ribosomal P-site elements m(2)G966, m(5)C967 and the C-terminal tail of the S9 protein in the fidelity of initiation of translation in Escherichia coli

The accuracy of pairing of the anticodon of the initiator tRNA (tRNA(fMet)) and the initiation codon of an mRNA, in the ribosomal P-site, is crucial for determining the translational reading frame. However, a direct role of any ribosomal element(s) in scrutinizing this pairing is unknown. The P-site elements, m(2)G966 (methylated by RsmD), m(5)C967 (methylated by RsmB) and the C-terminal tail of the protein S9 lie in the vicinity of tRNA(fMet). We investigated the role of these elements in initiation from various codons, namely, AUG, GUG, UUG, CUG, AUA, AUU, AUC and ACG with tRNA(CAU)(fmet) (tRNA(fMet) with CAU anticodon); CAC and CAU with tRNA(GUG)(fme); UAG with tRNA(GAU)(fMet) using in vivo and computational methods. Although RsmB deficiency did not impact initiation from most codons, RsmD deficiency increased initiation from AUA, CAC and CAU (2- to 3.6-fold). Deletion of the S9 C-terminal tail resulted in poorer initiation from UUG, GUG and CUG, but in increased initiation from CAC, CAU and UAC codons (up to 4-fold). Also, the S9 tail suppressed initiation with tRNA(CAU)(fMet)lacking the 3GC base pairs in the anticodon stem. These observations suggest distinctive roles of 966/967 methylations and the S9 tail in initiation.

Role of the Ribosomal P-Site Elements of m(2)G966, m(5)C967, and the S9 C-Terminal Tail in Maintenance of the Reading Frame during Translational Elongation in Escherichia coli

The ribosomal P-site hosts the peptidyl-tRNAs during translation elongation. Which P-site elements support these tRNA species to maintain codon-anticodon interactions has remained unclear. We investigated the effects of P-site features of methylations of G966, C967, and the conserved C-terminal tail sequence of Ser, Lys, and Arg (SKR) of the S9 ribosomal protein in maintenance of the translational reading frame of an mRNA. We generated Escherichia coli strains deleted for the SKR sequence in S9 ribosomal protein, RsmB (which methylates C967), and RsmD (which methylates G966) and used them to translate LacZ from its +1 and -1 out-of-frame constructs. We show that the S9 SKR tail prevents both the +1 and -1 frameshifts and plays a general role in holding the P-site tRNA/peptidyl-tRNA in place. In contrast, the G966 and C967 methylations did not make a direct contribution to the maintenance of the translational frame of an mRNA. However, deletion of rsmB in the S9 Delta 3 background caused significantly increased -1 frameshifting at 37 degrees C. Interestingly, the effects of the deficiency of C967 methylation were annulled when the E. coli strain was grown at 30 degrees C, supporting its context-dependent role.

N-Terminal disordered domain of saccharomyces cerevisiae Hop1 protein Is dispensable for DNA binding, bridging, and synapsis of double-stranded DNA molecules but is ecessary for spore formation

The cytological architecture of the synaptonemal complex (SC), a meiosis-specific proteinaceous structure, is evolutionarily conserved among eukaryotes. However, little is known about the biochemical properties of SC components or the mechanisms underlying their roles in meiotic chromosome synapsis and recombination. Functional analysis of Saccharomyces cerevisiae Hop1, a key structural component of SC, has begun to reveal important insights into its function in interhomolog recombination. Previously, we showed that Hop1 is a structure-specific DNA-binding protein, exhibits higher binding affinity for the Holliday junction, and induces structural distortion at the core of the junction. Furthermore, Hop1 promotes DNA condensation and intra- and intermolecular synapsis between duplex DNA molecules. Here, we show that Hop1 possesses a modular domain organization, consisting of an intrinsically disordered N-terminal domain and a protease-resistant C-terminal domain (Hop1CTD). Furthermore, we found that Hop1CTD exhibits strong homotypic as well as heterotypic protein protein interactions, and its biochemical activities were similar to those of the full-length Hop1 protein. However, Hop1CTD failed to complement the meiotic recombination defects of the Delta hop1 strain, indicating that both N- and C-terminal domains of Hop1 are essential for meiosis and spore formation. Altogether, our findings reveal novel insights into the structure-function relationships of Hop1 and help to further our understanding of its role in meiotic chromosome synapsis and recombination.

Non-singular terminal sliding mode guidance and control with terminal angle constraints for non-maneuvering targets

In this paper guidance laws to intercept stationary and constant velocity targets at a desired impact angle, based on sliding mode control theory, are proposed. The desired impact angle, which is defined in terms of a desired line-of-sight (LOS) angle, is achieved in finite time by selecting the missile's lateral acceleration (latax) to enforce non-singular terminal sliding mode on a switching surface designed using this desired LOS angle and based on non-linear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance laws for different initial engagement geometries and impact angles.

A Novel C-Terminal Homologue of Aha1 Co-Chaperone Binds to Heat Shock Protein 90 and Stimulates Its ATPase Activity in Entamoeba histolytica

Cytosolic heat shock protein 90 (Hsp90) has been shown to be essential for many infectious pathogens and is considered a potential target for drug development. In this study, we have carried out biochemical characterization of Hsp90 from a poorly studied protozoan parasite of clinical importance, Entamoeba histolytica. We have shown that Entamoeba Hsp90 can bind to both ATP and its pharmacological inhibitor, 17-AAG (17-allylamino-17-demethoxygeldanamycin), with K-d values of 365.2 and 10.77 mu M, respectively, and it has a weak ATPase activity with a catalytic efficiency of 4.12 x 10(-4) min(-1) mu M-1. Using inhibitor 17-AAG, we have shown dependence of Entamoeba on Hsp90 for its growth and survival. Hsp90 function is regulated by various co-chaperones. Previous studies suggest a lack of several important co-chaperones in E. histolytica. In this study, we describe the presence of a novel homologue of co-chaperone Aha1 (activator of Hsp90 ATPase), EhAha1c, lacking a canonical Aha1 N-terminal domain. We also show that EhAha1c is capable of binding and stimulating ATPase activity of EhHsp90. In addition to highlighting the potential of Hsp90 inhibitors as drugs against amoebiasis, our study highlights the importance of E. histolytica in understanding the evolution of Hsp90 and its co-chaperone repertoire. (C) 2014 Elsevier Ltd. All rights reserved.