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Twinned Crystal (twinned + crystal)

Distribution by Scientific Domains
Chemistry92%
2 Other Domains8%

Selected Abstracts

,1[Cu7] Cluster in SrCu7In6 , Synthesis and Structure Refinement of a Twinned Crystal.

CHEMINFORM, Issue 13 2004
Vasyl' I. Zaremba
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Twinned crystals and anomalous phasing

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2003
Zbigniew Dauter
Merohedral or pseudomerohedral twinning of crystals cannot be identified from inspection of the diffraction patterns. Several methods for the identification of twinning and the estimation of the twin fraction are suitable for macro­molecular crystals and all are based on the statistical properties of the measured diffraction intensities. If the crystal twin fraction is estimated and is not too close to 0.5, the diffraction data can be detwinned; that is, related to the individual crystal specimen. However, the detwinning procedure invariably introduces additional inaccuracies to the estimated intensities, which substantially increase when the twin fraction approaches 0.5. In some cases, a crystal structure can be solved with the original twinned data by standard techniques such as molecular replacement, multiple isomorphous replacement or multiwavelength anomalous diffraction. Test calculations on data collected from a twinned crystal of gpD, the bacteriophage , capsid protein, show that the single-wavelength anomalous diffraction (SAD) method can be used to solve its structure even if the data set corresponds to a perfectly twinned crystal with a twin fraction of 0.5. [source]

Twinned crystals of adeno-associated virus serotype 3b prove suitable for structural studies

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2009
Thomas F. Lerch
Adeno-associated viruses (AAVs) are leading candidate vectors for gene-therapy applications. The AAV-3b capsid is closely related to the well characterized AAV-2 capsid (87% identity), but sequence and presumably structural differences lead to distinct cell-entry and immune-recognition properties. In an effort to understand these differences and to perhaps harness them, diffraction-quality crystals of purified infectious AAV-3b particles have been grown and several partial diffraction data sets have been recorded. The crystals displayed varying levels of merohedral twinning that in earlier times would have rendered them unsuitable for structure determination, but here is shown to be a tractable complication. [source]

The structure and evolution of the murine inhibitor of carbonic anhydrase: A member of the transferrin superfamily

PROTEIN SCIENCE, Issue 9 2010
Brian E. Eckenroth
Abstract The original signature of the transferrin (TF) family of proteins was the ability to bind ferric iron with high affinity in the cleft of each of two homologous lobes. However, in recent years, new family members that do not bind iron have been discovered. One new member is the inhibitor of carbonic anhydrase (ICA), which as its name indicates, binds to and strongly inhibits certain isoforms of carbonic anhydrase. Recently, mouse ICA has been expressed as a recombinant protein in a mammalian cell system. Here, we describe the 2.4 Å structure of mouse ICA from a pseudomerohedral twinned crystal. As predicted, the structure is bilobal, comprised of two ,-, domains per lobe typical of the other family members. As with all but insect TFs, the structure includes the unusual reverse ,-turn in each lobe. The structure is consistent with the fact that introduction of two mutations in the N-lobe of murine ICA (mICA) (W124R and S188Y) allowed it to bind iron with high affinity. Unexpectedly, both lobes of the mICA were found in the closed conformation usually associated with presence of iron in the cleft, and making the structure most similar to diferric pig TF. Two new ICA family members (guinea pig and horse) were identified from genomic sequences and used in evolutionary comparisons. Additionally, a comparison of selection pressure (dN/dS) on functional residues reveals some interesting insights into the evolution of the TF family including that the N-lobe of lactoferrin may be in the process of eliminating its iron binding function. [source]

Growth process of the ridge,trough faces of a twinned crystal

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2005
Jae-Wook Lee
For a twinned face-centered-cubic crystal, the energy barrier for two-dimensional nucleation on a concave trough (or a re-entrant edge) and that for a layer advancing across a convex ridge were calculated. The former was obtained by analyzing the line tension of the trough. The results show that their energy barriers are 39 and 50% compared to that for nucleation on a flat {111} face, respectively. Therefore, the layer advance across the ridge is found to be more difficult than the nucleation on the trough. Based on these results, the morphology of the growing surface is predicted and an alternative growth process by the twin-plane-re-entrant-edge mechanism is suggested. [source]

Incommensurately modulated lanthanide coinage-metal diarsenides.

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009

Rare-earth metal coinage-metal diarsenides LnTAs2 (Ln = Y, La, Ce,Lu; T = Cu, Ag, Au) are known to crystallize in structures closely related to the HfCuSi2 type, which comprises a stacking sequence of puckered TAs layers and planar square As nets, separated by the Ln atoms. CeAu1,,As2, with , = 0.015,(2), shows an incommensurate positional modulation of the arsenic atoms in the planar As nets. Based on X-ray diffraction data on a twinned crystal, a structure model in the monoclinic superspace group P121/m1(,0,)00 (No. 11.1) with basic unit-cell parameters of a = 5.804,(1), b = 5.814,(1), c = 10.179,(1),Å and , = 90.09,(8)° is presented. The components of the modulation wavevector q = ,a* + 0b* + ,c* are , = 0.08,(1) and , = 0.39,(1). The structure comprises cis,trans chains and rectangles of As atoms and displays an intricate stacking sequence of the modulated arsenic nets. Rod groups and layer groups of the respective arrangements are identified and the arrangement of different motifs of the modulated As net is discussed. [source]

Two polymorphs of chlorido(cyclohexyldiphenylphosphine)gold(I)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010
Ilia A. Guzei
The title compound, [AuCl(C18H21P)], a monomeric two-coordinate gold(I) complex, has been characterized at 100,K as two distinct monoclinic polymorphs, one from a single crystal, (Is), and one from a pseudo-merohedrally twinned crystal, (It). The molecular structures in the two monoclinic [P21/n for (Is) and P21/c for (It)] polymorphs are similar; however, the packing arrangements in the two lattices differ considerably. The structure of (It) is pseudo-merohedrally twinned by a twofold rotation about the a* axis. [source]

gem -Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009
Michael G. Edwards
The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem -dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C23H26O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry. [source]

NH4Ag3(PO3F)2, a layered monofluorophosphate(V) with seven different Ag sites

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2007
Matthias Weil
Single crystals of ammonium trisilver bis[fluorophosphate(V)], NH4Ag3(PO3F)2, were obtained from an aqueous solution and the structure was refined from a racemically twinned crystal. The asymmetric unit contains seven crystallographically distinct Ag atoms (two of which are located on twofold axes), four PO3F tetrahedra and two ammonium cations. The layered structure is composed of silver,monofluorophosphate sheets, [Ag3(PO3F)2],, that extend parallel to (100). The F atoms of the PO3F tetrahedra point towards the ammonium cations, which are located in the interlayer space and stabilize the structure via moderate N,H...O and N,H...F hydrogen bonds. [source]

Pseudo-merohedral twinning in monoclinic crystals of wild-type human brain neuroglobin

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009
Djemel Hamdane
The purification, crystallization and successful structure determination by molecular replacement of wild-type human brain neuroglobin at 1.8,Å resolution is reported. The apparent space group was orthorhombic C2221, but the real space group was monoclinic P21, which resulted from twinning. Indeed, the unit-cell parameters, a = 31.2, b = 139.1, c = 31.2,Å, , = 102°, display a fortuitously close to c and twinning by the operator l, ,k, h occurs. Twinning was not evident from the initial analysis of intensity distribution, but pseudo-merohedral twinning was revealed by the Padilla and Yeates test based on local intensity differences. A twinning fraction of 0.5 was determined in SHELXL, indicating a perfect hemihedrally twinned crystal. To date, this type of twinning has been reported in more than ten structures, which makes it quite a common case in proteins. [source]

Structure of a pseudomerohedrally twinned monoclinic crystal form of a pyridoxal phosphate-dependent catalytic antibody

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2005
Béatrice Golinelli-Pimpaneau
The purification, crystallization and structure determination at 2.3,Å resolution of the complex of the pyridoxal-5,-phosphate (PLP) dependent catalytic antibody 15A9 with a phosphopyridoxyl- l -alanine (PPL- l -alanine) substrate analogue are described. The crystal belongs to space group P21, with two molecules in the asymmetric unit related by non-crystallographic symmetry. The unit-cell parameters are a = 63.5, b = 81.7, c = 79.3,Å and , is fortuitously 90°. Refinement of the structure converged at unacceptably high R factors. Although the traditional analysis of intensity distribution did not indicate twinning, pseudomerohedral twinning was revealed by a newer test based on local intensity differences [Padilla & Yeates (2003), Acta Cryst. D59, 1124,1130]. When the potential twinning operator was included in SHELX, the structure could be satisfactorily refined with a twinning fraction of 0.46, indicating a nearly perfect hemihedrally twinned crystal. One of the active sites is occupied by the phosphopyridoxyl- l -alanine ligand, while one iodide ion mimics the cofactor phosphate group in the other. Four other iodide ions are present in the structure: two are involved in specific intermolecular contacts and two dictate the conformation of the CDRH3 loop in each molecule. [source]

Twinned crystals and anomalous phasing

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2003
Zbigniew Dauter
Merohedral or pseudomerohedral twinning of crystals cannot be identified from inspection of the diffraction patterns. Several methods for the identification of twinning and the estimation of the twin fraction are suitable for macro­molecular crystals and all are based on the statistical properties of the measured diffraction intensities. If the crystal twin fraction is estimated and is not too close to 0.5, the diffraction data can be detwinned; that is, related to the individual crystal specimen. However, the detwinning procedure invariably introduces additional inaccuracies to the estimated intensities, which substantially increase when the twin fraction approaches 0.5. In some cases, a crystal structure can be solved with the original twinned data by standard techniques such as molecular replacement, multiple isomorphous replacement or multiwavelength anomalous diffraction. Test calculations on data collected from a twinned crystal of gpD, the bacteriophage , capsid protein, show that the single-wavelength anomalous diffraction (SAD) method can be used to solve its structure even if the data set corresponds to a perfectly twinned crystal with a twin fraction of 0.5. [source]

Structure determination of a cocaine hydrolytic antibody from a pseudomerohedrally twinned crystal

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2002
Nicholas A. Larsen
Few examples of pseudomerohedrally twinned macromolecular crystals have been described in the literature. This unusual phenomenon arises when a fortuitous unit-cell geometry makes it possible for twinning to occur in a space group that ordinarily does not allow twinning. Here, the crystallization, structure determination and refinement of the cocaine hydrolytic antibody 15A10 at 2.35,Å resolution are described. The crystal belongs to space group P21, with two molecules in the asymmetric unit and unit-cell parameters a = 37.5, b = 108.4, c = 111.3,Å and , fortuitously near 90°; the refined twinning fraction is , = 0.43. Interestingly, the non-crystallographic symmetry (NCS) and twin operators are nearly parallel, which appears to be a relatively frequent situation in protein crystals twinned by merohedry or pseudomerohedry. [source]

X-ray analysis of bilirubin oxidase from Myrothecium verrucaria at 2.3,Å resolution using a twinned crystal

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2010
Kimihiko Mizutani
Bilirubin oxidase (BOD), a multicopper oxidase found in Myrothecium verrucaria, catalyzes the oxidation of bilirubin to biliverdin. Oxygen is the electron acceptor and is reduced to water. BOD is used for diagnostic analysis of bilirubin in serum and has attracted considerable attention as an enzymatic catalyst for the cathode of biofuel cells that work under neutral conditions. Here, the crystal structure of BOD is reported for the first time. Blue bipyramid-shaped crystals of BOD obtained in 2-methyl-2,4-pentanediol (MPD) and ammonium sulfate solution were merohedrally twinned in space group P63. Structure determination was achieved by the single anomalous diffraction (SAD) method using the anomalous diffraction of Cu atoms and synchrotron radiation and twin refinement was performed in the resolution range 33,2.3,Å. The overall organization of BOD is almost the same as that of other multicopper oxidases: the protein is folded into three domains and a total of four copper-binding sites are found in domains 1 and 3. Although the four copper-binding sites were almost identical to those of other multicopper oxidases, the hydrophilic Asn residue (at the same position as a hydrophobic residue such as Leu in other multicopper oxidases) very close to the type I copper might contribute to the characteristically high redox potential of BOD. [source]

Illuminating Dark Plasmons of Silver Nanoantenna Rings to Enhance Exciton,Plasmon Interactions

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2009
Hong-Mei Gong
Abstract The chemical growth of silver nanorings that possess singly twinned crystals and a circular cross section via a reductive reaction solution is reported. The wire and ring diameters of the synthesized nanorings are in the ranges 80,200,nm and 4.5,18.0,,m, respectively. By lighting up the multipolar dark plasmons with slanted illumination, the silver nanoring exhibits unique focused scattering and large local-field enhancement. We also demonstrate strong exciton,plasmon interactions between a monolayer of CdSe/ZnS semiconductor quantum dots and a single silver antenna-like nanoring (nanoantenna) at the "hot spots" located at the cross points of the incident plane and nanoring; the position of these spots are tunable by adjusting the incidence angle of illumination. The tunable plasmonic behavior of the silver nanorings could find applications as optical nanoantennae or plasmonic nanocavities. [source]

Planar deformation features and impact glass in inclusions from the Vredefort Granophyre, South Africa

METEORITICS & PLANETARY SCIENCE, Issue 6 2002
P. C. Buchanan
This unit contains inclusions of country rock that were derived from different locations within the impact structure and are predominantly composed of quartzite, feldspathic quartzite, arkose, and granitic material with minor proportions of shale and epidiorite. Two of the least recrystallized inclusions contain quartz with single or multiple sets of planar deformation features. Quartz grains in other inclusions display a vermicular texture, which is reminiscent of checkerboard feldspar. Feldspars range from large, twinned crystals in some inclusions to fine-grained aggregates that apparently are the product of decomposition of larger primary crystals. In rare inclusions, a mafic mineral, probably biotite or amphibole, has been transformed to very fine-grained aggregates of secondary phases that include small euhedral crystals of Fe-rich spinel. These data indicate that inclusions within the Vredefort Granophyre were exposed to shock pressures ranging from <5 to 8,30 GPa. Many of these inclusions contain small, rounded melt pockets composed of a groundmass of devitrified or metamorphosed glass containing microlites of a variety of minerals, including K-feldspar, quartz, augite, low-Ca pyroxene, and magnetite. The composition of this devitrified glass varies from inclusion to inclusion, but is generally consistent with a mixture of quartz and feldspar with minor proportions of mafic minerals. In the case of granitoid inclusions, melt pockets commonly occur at the boundaries between feldspar and quartz grains. In metasedimentary inclusions, some of these melt pockets contain remnants of partially melted feldspar grains. These melt pockets may have formed by eutectic melting caused by inclusion of these fragments in the hot (650 to 1610 °C) impact melt that crystallized to form the Vredefort Granophyre. [source]

The derivation of twin laws in non-merohedric twins.

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2006
Application to the analysis of hybrid twins
An algorithm is presented to derive the twin laws in non-merohedric twins through the systematic search for quasi-perpendicular lattice planes/directions. The twin lattice, i.e. the sublattice common to the whole crystalline edifice built by the twinned individuals, is based on a supercell of the individual defined by a pair of quasi-perpendicular lattice elements (hkl)/[uvw]. Starting from a (real or supposed) twin element, (hkl) or [uvw], the set of quasi-perpendicular lattice elements with user-defined limits on the twin index and obliquity is explored. The degree of lattice quasi-restoration is commonly measured by the classical twin index but in some cases, especially for large supercells, this index represents only a first approximation of the degree of lattice quasi-restoration, because more than one pair (hkl)/[uvw] may exist, and more than one concurrent sublattices of nodes, based on the same twin element, may be quasi-restored, although within different obliquities. These twins, whose existence has been recently recognized, are termed hybrid twins. In hybrid twins, the degree of lattice quasi-restoration is measured by the effective twin indexnE, a generalization of the classical twin index: in the limiting case of only one (quasi-)restored sublattice, the effective twin index and the classical twin index coincide. A number of examples previously reported simply as `non-Friedelian' twins (with a twin index higher than the empirical limit of 6 established by Friedel) are analysed and reinterpreted as hybrid twins. A Fortran program is made available, which derives the possible twin laws according to this algorithm and analyses the pseudosymmetry of the concurrent sublattices defined by each pair (hkl)/[uvw]. The occurrence of hybrid concurrent components in twinning does not affect the normal procedures of dealing with diffraction patterns of twinned crystals. [source]

Bis(di-2-pyridylamine-,2N2,N2,)(nitrato-,2O,O,)nickel(II) nitrate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Juraj, ernák
In the ionic title compound, [Ni(NO3)(C10H9N3)2]NO3, the central NiII atom exhibits cis -NiN4O2 octahedral coordination with three chelating ligands, viz. one nitrate anion and two di-2-pyridylamine (dpya) molecules. A second nitrate group acts as a counter-ion. The complex cations and the nitrate anions are also linked by N,H...O hydrogen bonds. The compound was prepared in two different reproducible ways: direct synthesis from Ni(NO3)2 and dpya yielded systematically twinned crystals (the twinning law is discussed), while single crystals were obtained unexpectedly from the Ni(NO3)2/dpya/maleic acid/NaOH system. [source]

cis,cis -Ceratospong­amide N,N -di­methyl­acet­amide hemisolvate in the presence of twinning

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2003
Akiko Asano
Ceratospong­amide (CS) is a potent inhibitor of secreted phospho­lipase A2, and cis,cis and trans,trans isomers, related with respect to the two proline amide bonds, are known. Crystals of cis,cis -CS were grown from N,N -di­methyl­acet­amide solution, giving the title compound, the cyclic ester of isoleucyl­oxazolinyl­phenyl­alanyl­prolyl­thia­zolyl­phenyl­alanyl­pro­line [cyclo(-Ile,Oxz,Phe,Pro,Thz,Phe,Pro-)] N,N -di­methyl­acet­amide hemisolvate, C41H49N7O6S·0.5C4H9NO. The structure is the third example of cis,cis -CS to be investigated and comprises twinned crystals, in which the a and b axes are interchanged. The ratio of co-existing twin crystals is approximately 50%. The peptide has a `saddle-like' structure and is very similar to previously reported structures of cis,cis -CS, which implies that the structure of cis,cis -CS is very stable in spite of differences in crystallization conditions. [source]

Estimates of the twinning fraction for macromolecular crystals using statistical models accounting for experimental errors

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2007
Vladimir Y. Lunin
An advanced statistical model is suggested that is designed to estimate the twinning fraction in merohedrally (or pseudo-merohedrally) twinned crystals. The model takes experimental errors of the measured intensities into account and is adapted to the accuracy of a particular X-ray experiment through the standard deviations of the reflection intensities. The theoretical probability distributions for the improved model are calculated using a Monte Carlo-type simulation procedure. The use of different statistical criteria (including likelihood) to estimate the optimal twinning-fraction value is discussed. The improved model enables better agreement of theoretical and observed cumulative distribution functions to be obtained and produces twinning-fraction estimates that are closer to the refined values in comparison to the conventional model, which disregards experimental errors. The results of the two approaches converge when applied to selected subsets of measured intensities of high accuracy. [source]

Crystallization and preliminary X-ray analysis of pseudo-merohedrally twinned crystals of the full-length ,2 subunit of the Kv1 K+ channel from Rattus norvegicus

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2004
Tatsuro Shimamura
The eukaryotic Kv1 voltage-gated K+ channel is composed of four , subunits and four , subunits. The full-length ,2 subunit from Rattus norvegicus has been expressed in Esherichia coli, purified and then crystallized. A careful molecular-replacement study using the structure of the truncated ,2 subunit reveals that the crystals are perfectly pseudo-merohedrally twinned. While the apparent space group of the crystals was P4212, the real space group was shown to be P21212, with unit-cell parameters a = 222.6, b = 222.6, c = 82.3,Å. An asymmetric unit of the crystal contains two ,2 tetramers (MW = 340,kDa). A data set was collected from a crystal to 2.0,Å resolution, with 266,659 independent observations (93.0% complete) and Rmerge = 0.06. Although the crystals are perfectly twinned, they are still suitable for structural determination by molecular replacement using the truncated ,2 -subunit structure. [source]

MIR phasing using merohedrally twinned crystals

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2003
Anke C. Terwisscha van Scheltinga
Merohedral twinning is a crystal-growth disorder that seriously hinders the determination of macromolecular crystal structures by isomorphous replacement. The strategies used in the structures solved so far are discussed. Several methods can be used to determine the extent of twinning, the twin fraction and to detwin the data. Accurate determination of the twin fraction by analysing heavy-atom refinement statistics is possible, but only influences the resulting phases slightly. It seems more crucial to restrict the variation in twin fractions between data sets, either by making the twin fractions of some data sets artificially higher or by screening crystals to obtain data with a low twin fraction. [source]

Multiple isomorphous replacement on merohedral twins: structure determination of deacetoxycephalosporin C synthase

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2001
Anke C. Terwisscha van Scheltinga
Merohedral twinning is a packing anomaly that seriously impairs the determination of macromolecular crystal ­structures. Crystals of deacetoxycephalosporin C synthase (DAOCS), an enzyme involved in the expansion of the penicillin nucleus to form the core structure of the cephalosporin antibiotics, were found to be merohedrally twinned by many diagnostic criteria. Here, the structure determination of DAOCS from twinned crystals based on a combination of isomorphous replacement and the use of a multiple-wavelength diffraction data set is described. [source]

Preliminary X-ray analysis of twinned crystals of sarcosine dimethylglycine methyltransferase from Halorhodospira halochoris

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2009
Juha Pekka Kallio
Sarcosine dimethylglycine methyltransferase (EC 2.1.1.157) is an enzyme from the extremely halophilic anaerobic bacterium Halorhodospira halochoris. This enzyme catalyzes the twofold methylation of sarcosine to betaine, with S -adenosylmethionine (AdoMet) as the methyl-group donor. This study presents the crystallization and preliminary X-ray analysis of recombinant sarcosine dimethylglycine methyltransferase produced in Escherichia coli. Mass spectroscopy was used to determine the purity and homogeneity of the enzyme material. Two different crystal forms, which initially appeared to be hexagonal and tetragonal, were obtained. However, on analyzing the diffraction data it was discovered that both crystal forms were pseudo-merohedrally twinned. The true crystal systems were monoclinic and orthorhombic. The monoclinic crystal diffracted to a maximum of 2.15,Å resolution and the orthorhombic crystal diffracted to 1.8,Å resolution. [source]

Improvement of crystal quality by surface mutations of ,-lactamase Toho-1

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2009
Tatsuro Shimamura
The ,-lactamase Toho-1 exhibits a strong tendency to form merohedrally twinned crystals. Here, the crystal quality of Toho-1 was improved by using surface modification to remove a sulfate ion involved in crystal packing. The surface-modified Toho-1 variant (R274N/R276N) was crystallized under similar conditions to those used for wild-type Toho-1. R274N/R276N did not form merohedrally twinned crystals. The crystals diffracted to a significantly higher resolution (,0.97,Å) than the wild-type crystals (1.65,Å); they belonged to the same space group and had almost identical unit-cell parameters to those of wild-type Toho-1. [source]