Showing papers by "George M. Sheldrick published in 2006"

Serendipitous SAD phasing of an echinomycin-(ACGTACGT)2 bisintercalation complex.

Abstract: A new crystal form was obtained for the complex between (ACGTACGT)2 and echinomycin and X-ray data were collected to 1.6 A. The structure was phased by the SAD method based on a single unexpected anomalous scatterer that could be identified as a mixture of nickel and zinc by measurements of the anomalous scattering at different wavelengths. This cation is coordinated by two guanines from two different duplexes and four water molecules. The structure resembles previously reported crystal structures of DNA–echinomycin complexes, except that three of the eight base pairs flanking the echinomycin bisintercalator sites have the Watson–Crick rather than the Hoogsteen configuration. Hoogsteen binding was found for the corresponding base pairs of the crystallographically independent duplex, indicating that the two configurations are very close in energy.

[Ni(S4)2]2⊖, ein homoleptischer Tetrasulfido‐Nickel(II)‐Komplex

Abstract: Le sel tetraethylammonium cristallise dans le groupe P4n2 avec a=1044,8 et c=1276,2 pm, Z=2. Affinement jusqu'a R=0,038

Structure of the C2A domain of rabphilin-3A.

Abstract: Rabphilin-3A is a neuronal protein containing a C2-domain tandem. To date, only the structure of the C2B domain has been solved. The crystal structure of the Ca2+-free C2A domain has been solved by molecular replacement and refined to 1.92 A resolution. It adopts the classical C2-domain fold consisting of an eight-stranded antiparallel β-sandwich with type I topology. In agreement with its Ca2+-dependent negatively charged membrane-binding properties, this C2 domain contains all the conserved acidic residues responsible for calcium binding. However, the replacement of a conserved aspartic acid residue by glutamic acid allows formation of an additional strong hydrogen bond, resulting in increased rigidity of calcium-binding loop 1. The electrostatic surface of the C2A domain consists of a large positively charged belt surrounded by two negatively charged patches located at both tips of the domain. In comparison, the structurally very similar C2A domain of synaptotagmin I has a highly acidic electrostatic surface, suggesting completely unrelated functions for these two C2A domains.

Programs and program systems in wide use

Abstract: Macromolecular programs and program systems in wide use are described. The chapter covers PHASES; DM/DMMULTI, software for phase improvement by density modification; the structure-determination language of the Crystallography & NMR System; the TNT refinement package; the ARP/wARP suite for automated construction and refinement of protein models; validation of protein-structure coordinates with PROCHECK; MolScript; MAGE, PROBE and kinemages; XDS; and macromolecular applications of SHELX.

Structural elucidation of the PDI-related chaperone Wind with the help of mutants.

Abstract: The structures of the PDI-related protein Wind (with a C-­terminal His6 tag) and the mutants Y53S, Y53F and Y55K have been determined and compared with the wild-type structure with the His6 tag at the N-terminus. All five structures show the same mode of dimerization, showing that this was not an artefact introduced by the nearby N-terminal His6 tag and suggesting that this dimer may also be the biologically active form. Although the mutants Y53S and Y55K completely abrogate transport of the protein Pipe (which appears to be the primary function of Wind in the cell), only subtle differences can be seen in the putative Pipe-binding region. The Pipe binding in the active forms appears to involve hydrophobic interactions between aromatic systems, whereas the inactive mutants may be able to bind more strongly with the help of hydrogen bonds, which could disturb the delicate equilibrium required for effective Pipe transport.

The EU BIOXHIT standard test crystal – verfiying Se-MAD beamlines

Abstract: The standard test crystal is designed to provide an automated, fast and robust procedure for identifying potential problems in the complex hardware and software infrastructure of modern protein crystallographic (PX) synchrotron beamlines. The resulting diagnostics should be independent of the data integration software employed (XDS, MOSFLM/SCALA and HKL2000). The cubic form of bovine insulin (space group I213) has proved to be a good first choice for a test crystal, with high reproducibility in crystal growth and freezing, high symmetry for highly redundant data collection, there is an additional need to verify the operation of MAD beamlines, in particular those used for phasing of selenomethionine derivatives. For this purpose we have synthesised an organoselenium compound that crystallises in the suitable space group P41212 and has four selenium atoms in general positions in the asymmetric unit. We have determined precise cell dimensions at various temperatures by X-ray powder diffraction to test the possibility that the cell can be reproduced well enough to provide a precise wavelength calibration for MAD beamlines. We will present our experiences with the new Se-MAD test crystal. We are grateful to the EU for support (LHSG-CT-2003503420) and to the other BIOXHIT partners for the fruitful collaboration. m06.o01