Hexagonal Crystal Form (hexagonal + crystal_form)

Distribution by Scientific Domains

Selected Abstracts

The structure of the hexagonal crystal form of hen egg-white lysozyme

M. S. Weiss
The three-dimensional structure of hen egg-white lysozyme (HEWL) in a hexagonal crystal form has been determined and refined to 1.46, resolution. This hexagonal crystal form crystallizes from a saturated sodium nitrate solution at pH 8.4. The crystals belong to space group P6122, with unit-cell parameters a = b = 85.64, c = 67.93,. A total of 165 water molecules, 16 nitrate ions and five sodium ions were located in the electron-density map. The hexagonal crystal form exhibits a higher solvent content and a higher degree of disorder than other crystal forms of lysozyme. The flexibility of the protein depends on the crystal packing, although some residue ranges are flexible in all native HEWL crystal forms. [source]

A new crystal form of XT6 enables a significant improvement of its diffraction quality and resolution

Maya Bar
Xylanases (1,4-,- d -xylan xylanhydrolases; EC hydrolyze the 1,4-,- d -xylopyranosyl linkage of xylans. The detailed structural characterization of these enzymes is of interest for the elucidation of their catalytic mechanism and for their rational modification toward improved stability and specificity. An extracellular xylanase from Geobacillus stearothermophilus T-6 (XT6) has recently been cloned, overexpressed, purified and biochemically characterized. Previous crystallographic efforts resulted in a hexagonal crystal form, which subsequently proved to be of limited use for structural analysis, mainly because of its relatively poor diffraction quality and resolution. A systematic search for more suitable crystals of XT6 recently resulted in a new crystal form of this enzyme with significantly improved diffraction characteristics. The new crystals belong to a C -centred monoclinic crystal system (space group C2), with unit-cell parameters a = 121.5, b = 61.7, c = 89.1,, , = 119.7. These crystals diffract X-rays to better than 1.5, resolution, showing a very clear diffraction pattern of relatively high quality. The crystals are mechanically strong and exhibit excellent radiation-stability when frozen under cold nitrogen gas. A full diffraction data set to 1.45, resolution (94.1% completeness, Rmerge = 7.0%) has been collected from flash-frozen crystals of the native enzyme at 95,K using synchrotron radiation. Crystals of the E159A/E265A catalytic double mutant of XT6 were found to be isomorphous to those of native XT6. They were used for a full measurement of 1.8, resolution diffraction data at 100,K (90.9% completeness; Rmerge = 5.0%). These data are currently being used for the high-resolution structure determination of XT6 and its mutant for mechanistic interpretations and rational introduction of thermostability. [source]

Definition of domain boundaries and crystallization of the SMN Tudor domain

Remco Sprangers
Spinal muscular atropy (SMA) is the major genetic disease leading to childhood mortality and is caused by mutations in or deletions of the smn1 gene. The human survival of motor neurons (SMN) protein encoded by this gene plays an important role in the assembly of snRNPs (small nuclear ribonucleoprotein complexes) via binding to the spliceosomal Sm proteins. The tails of these Sm proteins contain symmetrically dimethylated arginines that are recognized by the central SMN Tudor domain. To gain insight in the molecular basis of this specific interaction, the SMN Tudor domain has been crystallized. The rapid crystallization of the protein and the high stability of the crystals is facilitated by redefinition of domain boundaries based on NMR relaxation experiments and the previously determined solution structure. The crystals diffract to high resolution (1.8,) and a complete data set has been collected from a hexagonal crystal form (P61/P65), with unit-cell parameters a = b = 27.65, c = 110.30,, , = , = 90, , = 120. Crystal soaks and co-crystallization with peptides derived from the Sm protein tails have been initiated. Molecular replacement with the NMR coordinates is under way. [source]

Structures of feline immunodeficiency virus dUTP pyrophosphatase and its nucleotide complexes in three crystal forms

G. Sridhar Prasad
dUTP pyrophosphatase (dUTPase) cleaves the ,-, phosphodiester of dUTP to form pyrophosphate and dUMP, preventing incorporation of uracil into DNA and providing the substrate for thymine synthesis. Seven crystal structures of feline immunodeficiency virus (FIV) dUTPase in three crystal forms have been determined, including complexes with substrate (dUTP), product (dUMP) or inhibitor (dUDP) bound. The native enzyme has been refined at 1.40, resolution in a hexagonal crystal form and at 2.3, resolution in an orthorhombic crystal form. In the dUDP complex in a cubic crystal form refined at 2.5, resolution, the C-terminal conserved P-loop motif is fully ordered. The analysis defines the roles of five sequence motifs in interaction with uracil, deoxyribose and the ,-, ,- and ,-phosphates. The enzyme utilizes adaptive recognition to bind the ,- and ,-phosphates. In particular, the ,-, phosphodiester adopts an unfavorable eclipsed conformation in the presence of the P-loop. This conformation may be relevant to the mechanism of ,-, phosphodiester bond cleavage. [source]

Crystallization and preliminary X-ray diffraction analysis of the N-terminal domain of Mrs2, a magnesium ion transporter from yeast inner mitochondrial membrane

Muhammad Bashir Khan
Mrs2 transporters are distantly related to the major bacterial Mg2+ transporter CorA and to Alr1, which is found in the plasma membranes of lower eukaryotes. Common features of all Mrs2 proteins are the presence of an N-terminal soluble domain followed by two adjacent transmembrane helices (TM1 and TM2) near the C-terminus and of the highly conserved F/Y-G-M-N sequence motif at the end of TM1. The inner mitochondrial domain of the Mrs2 from Saccharomyces cerevisae was overexpressed, purified and crystallized in two different crystal forms corresponding to an orthorhombic and a hexagonal space group. The crystals diffracted X-rays to 1.83 and 4.16, resolution, respectively. Matthews volume calculations suggested the presence of one molecule per asymmetric unit in the orthorhombic crystal form and of five or six molecules per asymmetric unit in the hexagonal crystal form. The phase problem was solved for the orthorhombic form by a single-wavelength anomalous dispersion experiment exploiting the sulfur anomalous signal. [source]

Cloning, expression, purification, crystallization and preliminary crystallographic studies of UgdG, an UDP-glucose dehydrogenase from Sphingomonas elodea ATCC 31461

Joana Rocha
Gellan gum, a commercial gelling agent produced by Sphingomonas elodea ATCC 31461, is a high-value microbial exopolysaccharide. UDP-glucose dehydrogenase (UGD; EC is responsible for the NAD-dependent twofold oxidation of UDP-glucose to UDP-glucuronic acid, one of the key components for gellan biosynthesis. S. elodea ATCC 31461 UGD, termed UgdG, was cloned, expressed, purified and crystallized in native and SeMet-derivatized forms in hexagonal and tetragonal space groups, respectively; the crystals diffracted X-rays to 2.40 and 3.40, resolution, respectively. Experimental phases were obtained for the tetragonal SeMet-derivatized crystal form by a single-wavelength anomalous dispersion experiment. This structure was successfully used as a molecular-replacement probe for the hexagonal crystal form of the native protein. [source]

Reductive methylation to improve crystallization of the putative oxidoreductase Rv0765c from Mycobacterium tuberculosis

Wilko Rauert
Rv0765c from Mycobacterium tuberculosis was cloned and heterologously expressed in Escherichia coli. It was purified using affinity and size-exclusion chromatographic techniques and crystallized. The native protein crystallized in a hexagonal crystal form which diffracted to 7, resolution. In an attempt to improve the quality of the Rv0765c crystals, the protein was modified by reductive methylation using dimethylaminoborane and formaldehyde. The modified protein crystallized under different conditions in a tetragonal crystal form, from which diffraction data could be collected to a resolution of 3.2,. In both crystal forms of Rv0765c, the asymmetric unit contained two copies of the protein molecule. [source]