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Acta Cryst. (2014). A70, C1211
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Soluble inorganic pyrophosphatase (IPPase) catalyzes the hydrolysis of inorganic pyrophosphate (PPi) to form orthophosphate (Pi). The action of this enzyme shifts the overall equilibrium in favor of synthesis during a number of ATP-dependent cellular processes such as in the polymerization of nucleic acids, production of coenzymes and proteins and sulfate assimilation pathways. Two Neutron crystallographic (2.10-2.50Å) and five high-resolution X-ray (0.99Å-1.92Å) structures of the archaeal IPPase from Thermococcus thioreducens have been determined under both cryo and room temperatures. The structures determined include the recombinant IPPase bound to Mg+2, Ca+2, Br-, SO2-2 or PO4-2 involving those with non-hydrolyzed and hydrolyzed pyrophosphate complexes. All the crystallographic structures provide snapshots of the active site corresponding to different stages of the hydrolysis of inorganic pyrophosphate. As a result, a structure-based model of IPPase catalysis is devised showing the enzyme's low-energy conformations, hydration states, movements and nucleophile generation within the active site.

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Acta Cryst. (2014). A70, C1215
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The research reactor Heinz Maier-Leibnitz (FRM II) is a modern high flux neutron source which feeds some 30 state of the art neutron beam instruments. Currently 24 are operational, others in commissioning or under construction. The newly built neutron single crystal diffractometer BIODIFF is especially designed to collect data from crystals with large unit cells. The main field of application is the structural analysis of proteins, especially the determination of hydrogen atom positions. BIODIFF is a joint project of the Jülich Centre for Neutron Science (JCNS) and the FRM II. Typical scientific questions addressed are the determination of protonation states of amino acid side chains (see e. g. [1,2]) and the characterization of the hydrogen bonding network between the protein active centre and an inhibitor or substrate. BIODIFF is designed as a monochromatic instrument. By using a highly orientated pyrolytic graphite monochromator (PG002) the diffractometer is able to operate in the wavelength range of 2.4 Å to about 5.6 Å. Contaminations of higher order wavelengths are removed by a neutron velocity selector. To cover a large solid angle the main detector of BIODIFF consists of a neutron imaging plate in a cylindrical geometry with online read-out capability. A fast Li/ZnS scintillator CCD camera is available for additional detection abilities. An optical CCD-camera pointing at the sample position is used to quickly align the crystal with respect to the neutron beam. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low. BIODIFF is equipped with a standard Oxford Cryosystem "Cryostream 700+" which allows measurements in the temperature regime from 90 K up to 500 K (see Figure underneath).
Keywords: neutron; protein; hydrogen.

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Acta Cryst. (2014). A70, C1220
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Nitrogen-containing bisphosphonates (N-BPs), such as risedronate and zoledronate, are currently used as clinical drug for bone-resorption diseases and are potent inhibitor of farnesyl pyrophosphate synthase (FPPS). The potential of N-BPs as antitumor agents has also been suggested by the several in vitro and in vivo preclinical studies. However, BP drugs limit their therapeutic use to bone-related diseases, because BPs are highly charged and water soluble molecules. X-ray crystallographic analyses of FPPS with N-BPs have revealed that N-BPs bind to FPPS with three magnesium ions and several water molecules. In order to develop a novel FPPS inhibitor, the hydrogen-bond networks formed by FPPS, BPs and water molecules are necessary to be elucidated. To understand the structural characteristics of N-BPs bound to FPPS, including hydrogen atoms and hydration by water, neutron diffraction studies were initiated using BIODIFF at the Heinz Maier-Leibnitz Zentrum (MLZ). FPPS-risedronate complex crystals of approximate dimensions 2.8 × 2.5 × 1.5 mm (~ 3.5 mm3) were obtained by repeated macro-seeding. Monochromatic neutron diffraction data were collected to 2.4 Å resolution with 98.4% overall completeness and 10.7% Rmerge. As a result of X-ray/neutron joint refinment, R and Rfree values for the neutron data were 19.6 and 23.3%, respectively. This neutron structure clearly reveals the protonation state of risedronate, hydration in the inhibitor-binding region. Furthermore, the amide H/D exchange analysis showed that there is a highly rigid region which regulate the structural change upon the binding of the ligands. Here we will discuss the detailed hydrogen-bond network and the protonation state of FPPS and risedronate.
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