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Acta Cryst. (2014). A70, C796
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BL17U at Shanghai Synchrotron Radiation Facility (SSRF) is a PX beamline designed to high resolution and high throughput structural determination of macromolecules and their complexes. Since it opened to user community at 2009, more than 800 structures are publicly deposited to PDB up to date by using the beamline. The beamline offer more than 160 research group beamtime, the beamtime is over subscribed seriously. Full automation is requested and the staffs keep improving the automation and convenience. Sample changer is critical for the remote operation, it let the users do not need to enter the hutch in their experiment. Several facilities have developed their own robot to achieve this purpose since ten years ago. While for a very shortly period to put the beamline in operation, we adopt the commercial robotics, ACTOR from RIGAKU company, as the sample changer. Users can put 5 uni-type pucks into the dewar one time, totally 80 cryocooled samples. The low level control software is offered by the vendor, although it is not open source, the software provide the API to further development, which can be used to integrate the robot to our software system. Under the help from SSRL, we implement the Blu-Ice/DCS system to our beamline for control and data acquisition [1]. Based on the Blu-Ice/DCS protocol [2], a new DHS is developed to integrate the ACTOR robot to Blu-Ice/DCS. All the function, such as the mount, exchange, dismount and anneal, are implemented as operations. Thus we can program the proper operation by the script engineer to meet the requirements. The intuitive GUI is in the same order as the PUCK in the dewar, the user just click the sample to mount and exchange their samples. Except the laser sensor used to make sure the sample mounted to goniohead successfully, at the same time the user can observe the mount process by the live video server which also integrated into the software. Thanks to the Blu-Ice, the multi GUI clients are supported. The authorized remote users connect to the facility intranet by VPN, by means of the NX client they can connect to the GUI computer on site, as shown in Figure 1. Then they can only run the GUI program for data collection, so the intranet network environment and the equipment are protected maximum.

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Acta Cryst. (2014). A70, C1451
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Determining the magnetic structure of material on a nanometer scale is fundamental for understanding its nano-scale magnetic property and developing nano-scale magnetic devices. Site-specific electron energy-loss magnetic chiral dichroism (site-specific EMCD[1],[2]) method is come up with to get the crystallographic site-specific magnetic information of nanostructures. By constructively using the dynamical diffraction conditions in EMCD experiments, we experimentally achieve the crystallographic site-specific magnetic structure of a nanostructure of NiFe2O4 as an example in transmission electron microscope, with its site-specific magnetic circular dichroism spectra, and its site-specific spin/orbital magnetic moments extracted. The site-specific EMCD method shows its unique capability for solving the crystallographic site-specific magnetic structure on nano-scale, compared with X-ray magnetic circular dichroism and neutron diffraction. This work may benefit the research and application of magnetic materials on a nanometer scale. Acknowledgement: This work is financially supported by National 973 Project of China (2009CB623701) and Chinese National Nature Science Foundation (11374174,51390471 ). This work made use of the resources of the Beijing National Center for Electron Microscopy.

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Acta Cryst. (2014). A70, C1683
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Thaxtomins, a family of phytotoxins produced by Streptomyces spp., can causes plant cell necrosis at nanomolar concentrations. Thaxtomin A is the dominant form from Streptomyces scabies and has demonstrated herbicidal action. TxtE, a cytochrome P450 enzyme from S. scabies 87.22, catalyzes direct nitration of the indolyl moiety of L-tryptophan to L-4-nitrotryptophan using nitric oxide, dioxygen and NADPH, which is the key step of Thaxtomin A biosynthesis. NO-related nitration is a common chemical process in organisms, particularly for tyrosine nitration. However, TxtE is the first reported enzyme that catalyzes a direct nitration reaction specifically in a biosynthetic pathway and thus it can potentially be developed for industrial applications. The crystal structure of TxtE was determined at 2.1 angstrom. A clearly defined substrate access channel is observed and can be classified as channel 2a, which is common in bacteria cytochrome P450 enzymes. A continuous hydrogen bond chain from the active site to the external solvent is observed. Compared with other cytochrome P450 enzymes, TxtE shows a unique proton transfer pathway which crosses the helix I distortion. Polar contacts of Arg59, Tyr89, Asn293, Thr296, and Glu394 with L-tryptophan are seen using molecular docking analysis, which are potentially important for substrate recognition and binding. After mutating Arg59, Asn293, Thr296 or Glu394 to leucine, the substrate binding ability of TxtE was lost or decreased significantly. According to docking and mutagenesis experiments, we propose a possible substrate recognition and binding mechanism, a possible mechanism for substrate recognition and binding is proposed.
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