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Xenon Derivative (xenon + derivative)
Selected AbstractsPhasing possibilities using different wavelengths with a xenon derivativeJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2002Santosh Panjikar Xenon derivatives are generally expected to be isomorphous with the native; however, the K - and L -absorption edges are not easily accessible on most synchrotron beamlines, which might limit their usefulness in phase determination. Various phasing procedures for xenon-derivatized porcine pancreatic elastase have been investigated using data sets measured at three generally accessible wavelengths. The importance of highly redundant data in measuring precise anomalous differences is highlighted and it is shown that, after such measurements, a single isomorphous replacement anomalous scattering (SIRAS) procedure yields a better phase set than those generated by single anomalous scattering (SAS) or multiwavelength anomalous diffraction (MAD) procedures. [source] Structure of lobster apocrustacyanin A1 using softer X-raysACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2001M. Cianci The molecular basis of the camouflage colouration of marine crustacea is often provided by carotenoproteins. The blue colour of the lobster carapace, for example, is intricately associated with a multimacromolecular 16-mer complex of protein subunits each with a bound astaxanthin molecule. The protein subunits of crustacyanin fall into two distinct subfamilies, CRTC and CRTA. Here, the crystal structure solution of the A1 protein of the CRTC subfamily is reported. The problematic nature of the structure solution of the CRTC proteins (both C1 and A1) warranted consideration and the development of new approaches. Three putative disulfides per protein subunit were likely to exist based on molecular-homology modelling against known lipocalin protein structures. With two such subunits per crystallographic asymmetric unit, this direct approach was still difficult as it involved detecting a weak signal from these sulfurs and suggested the use of softer X-rays, combined with high data multiplicity, as reported previously [Chayen et al. (2000), Acta Cryst. D56, 1064,1066]. This paper now describes the structure solution of CRTC in the form of the A1 dimer based on use of softer X-rays (2,Å wavelength). The structure solution involved a xenon derivative with an optimized xenon LI edge signal and a native data set. The hand of the xenon SIROAS phases was determined by using the sulfur anomalous signal from a high-multiplicity native data set also recorded at 2,Å wavelength. For refinement, a high-resolution data set was measured at short wavelength. All four data sets were collected at 100,K. The refined structure to 1.4,Å resolution based on 60,276 reflections has an R factor of 17.7% and an Rfree of 22.9% (3137 reflections). The structure is that of a typical lipocalin, being closely related to insecticyanin, to bilin-binding protein and to retinol-binding protein. This A1 monomer or dimer can now be used as a search motif in the structural studies of the oligomeric forms ,- and ,-crustacyanins, which contain bound astaxanthin molecules. [source] Purification, crystallization and X-ray diffraction analysis of pavine N -methyltransferase from Thalictrum flavumACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 11 2008Ankur Jain A cDNA from the plant Thalictrum flavum encoding pavine N -methyltransferase, an enzyme belonging to a novel class of S -adenosylmethionine-dependent N -methyltransferases specific for benzylisoquinoline alkaloids, has been heterologously expressed in Escherichia coli. The enzyme was purified using affinity and gel-filtration chromatography and was crystallized in space group P21. The structure was solved at 2.0,Å resolution using a xenon derivative and the single isomorphous replacement with anomalous scattering method. [source] Metal-free MIRAS phasing: structure of apo-S100A3ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2002Peer R. E. Mittl S100 proteins are involved in metal-dependent intracellular signalling. Metal-free S100A3, a cysteine-rich Ca2+ - and Zn2+ -binding protein, has been crystallized by vapour diffusion under the strict exclusion of oxygen and in the absence of divalent metal ions. Metal binding induces large conformational changes, rendering the apo-S100A3 crystals very sensitive to various metal compounds. Therefore, the structure was solved by MIRAS phasing using potassium iodide and xenon derivatives. Iodide replaces a water molecule at the surface of the S100A3 protein, whereas xenon binds in a hydrophobic cavity at the dimer interface. Despite significant non-isomorphism, the combination of both derivatives was sufficient for structure determination. The overall apo-S100A3 structure resembles the structures of metal-free S100B and S100A6 solution structures. In contrast to the NMR structures, the EF-hand loops are well ordered in the apo-S100A3 crystal structure. In the N-terminal pseudo-EF-hand loop a water molecule occupies the position of the Ca2+ ion. The C-terminal canonical EF-hand loop shows an extended conformation and a different helix arrangement to other S100/metal complex crystal structures. [source] | ||||||||||