Preliminary X-ray crystallographic analysis of 2-methylcitrate synthase from Salmonella typhimurium

Analysis of the genomic sequences of Escherichia coli and Salmonella typhimurium has revealed the presence of several homologues of the well studied citrate synthase (CS). One of these homologues has been shown to code for 2-methylcitrate synthase (2-MCS) activity. 2-MCS catalyzes one of the steps in the 2-methylcitric acid cycle found in these organisms for the degradation of propionate to pyruvate and succinate. In the present work, the gene coding for 2-MCS from S. typhimurium (StPrpC) was cloned in pRSET-C vector and overexpressed in E. coli. The protein was purified to homogeneity using Ni-NTA affinity chromatography. The purified protein was crystallized using the microbatch-under-oil method. The StPrpC crystals diffracted X-rays to 2.4 A resolution and belonged to the triclinic space group P1, with unit-cell parameters a = 92.068, b = 118.159, c = 120.659 A, alpha = 60.84, beta = 67.77, gamma = 81.92 degrees. Computation of rotation functions using the X-ray diffraction data shows that the protein is likely to be a decamer of identical subunits, unlike CSs, which are dimers or hexamers.

Crystal structures of a nonapeptide helix containing alpha,alpha-di-n-butylglycine (Dbg), Boc-Gly-Dbg-Ala-Val-Ala-Leu-Aib-Val-Leu-OMe

Two crystals structures of a nonapeptide (anhydrous and hydrated) containing the amino acid residue alpha, alpha-di-n-butylglycyl, reveal a mixed 3(10)/alpha-helical conformation. Residues 1-7 adopt phi, psi values in the helical region, with Val(8) being appreciably distorted. The Dbg residue has phi, psi values of -40, -37 degrees and -46, -40 degrees in two crystals with the two butyl side chains mostly extended in each. Peptide molecules in the crystals pack into helical columns. The crystal parameters are C50H91N9O12, space group P2(1), with a = 9.789(1) Angstrom, b = 20.240(2) Angstrom, c = 15.998(3) Angstrom, beta = 103.27(1); Z = 2, R = 10.3% for 1945 data observed >3 sigma(F) and C50H91N9O12. 3H(2)O, space group P2(1), with a = 9.747(3) Angstrom, b = 21.002(8) Angstrom, c = 15.885(6) Angstrom, beta = 102.22(3)degrees, Z = 2, R = 13.6% for 2535 data observed >3 sigma(F). The observation of a helical conformation at Dbg suggests that the higher homologs in the alpha, alpha-dialkylated glycine series also have a tendency to stabilize peptide helices. (C) Munksgaard 1996.

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I 'beta-turn forming tetrapeptide and an alpha-helical tetradecapeptide

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I' beta-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt alpha-helical conformations stabilized by 11 successive 5 -> 1 hydrogen bonds. In addition, a single 4 -> 1 hydrogen bond is also observed at the N-terminus. All live Dpg residues adopt backbone torsion angles (phi, psi) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle N-C-alpha-C' (tau) and the observed backbone phi,psi values. For tau > 106 degrees, helices are observed, while fully extended structures are characterized by tau < 106 degrees. The mean r values for extended and folded conformations for the Dpg residue are 103.6 degrees +/- 1.7 degrees and 109.9 degrees +/- 2.6 degrees, respectively. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

The syntheses, characterizations, X-ray crystal structures and properties of Cu(I) complexes of a bis-bidentate schiff base ligand

Bis-bidentate Schiff base ligand L and its two mononuclear complexes [CuL(CH3CN)(2)]ClO4 (1)and [CuL(PPh3)(2)]ClO4 (2)have been prepared and thoroughly characterized by elemental analyses, IR, UV-Vis, NMR spectroscopy and X-ray diffraction analysis. In both the complexes the metal ion auxiliaries adopt tetrahedral coordination environment. Their reactivity, electrochemical and photophysical behavior have been studied. Complex 1 shows reversible Cu-II/I couple with potential 0.74 V versus Ag/AgCl in CH2Cl2. At room temperature L is weakly fluorescent in CH2Cl2, however in Cu(I)complexes 1 and 2 the emission in quenched. (C) 2009 Elsevier B. V. All rights reserved.

Crystallization and Preliminary X-ray Studies of the Basic Lectin from Winged Bean (Psophocarpus tetragonolobus)

The basic lectin from winged bean (Psophocarpus tetragonolobus) could be crystallized using polyethyleneglycol (PEG) 4000 (I), PEG 8000 (II) and 2-methylpentane-2,4-diol (MPD) (III) as precipitants. Crystal forms I and II grew in the presence of methyl-α-Image -galactopyranoside or N -acetylgalactosamine while III grew in the absence of sugar. The three forms have the same space group (P21212) and similar unit cell dimensions with two dimeric molecules in the asymmetric unit. The unit cell dimensions are a = 156·8 Å, b = 89·0 Å, c = 73·3 Å for I, a = 155·5 Å, b = 92·3 Å, c = 72·5 Å for II and a = 148·3 Å, b = 90·7 Å, c = 73·8 Å for III. The crystals, particularly those grown using PEG 8000, are suitable for high resolution X-ray analysis, which is in progress.

A hybrid computer for X-ray crystallography

A hybrid computer for structure factor calculations in X-ray crystallography is described. The computer can calculate three-dimensional structure factors of up to 24 atoms in a single run and can generate the scatter functions of well over 100 atoms using Vand et al., or Forsyth and Wells approximations. The computer is essentially a digital computer with analog function generators, thus combining to advantage the economic data storage of digital systems and simple computing circuitry of analog systems. The digital part serially selects the data, computes and feeds the arguments into specially developed high precision digital-analog function generators, the outputs of which being d.c. voltages, are further processed by analog circuits and finally the sequential adder, which employs a novel digital voltmeter circuit, converts them back into digital form and accumulates them in a dekatron counter which displays the final result. The computer is also capable of carrying out 1-, 2-, or 3-dimensional Fourier summation, although in this case, the lack of sufficient storage space for the large number of coefficients involved, is a serious limitation at present.

A simple miniature furnace for routine collection of single crystal x-ray data up to 1000°C on the Hilger and Watts linear diffractometer

A miniature furnace suitable for routine collection of x-ray data up to 1000°C from single crystals on the Hilger and Watts linear diffractometer, without restricting the normally allowed region of reciprocal space on the diffractometer, is described. The crystal is heated primarily by radiation from a surrounding current-heated, stationary platinum coil wound on a silica bracket. The coil is split at its middle to provide a 4 mm gap for crystal mounting and x-irradiation. The crystal, mounted on a standard goniometer head, can be rotated and centred freely, as in the room temperature case. There is no need for any radiation shields or water-cooling arrangement. Investigations up to 1500°C are possible with slight modifications of the furnace.

The absolute configuration of echitamine iodide by the X-ray technique

The absolute configuration of echitamine iodide has been determined by the Bijvoet technique, making use of the intensity differences between hkl and {Mathematical expression} reflections due to the anomalous scattering of CuKa radiation by the iodine atom. The various steps in the procedure are discussed in detail in this paper.

Alignment of the ALICE Inner Tracking System with cosmic-ray tracks

ALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.