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Rfree Values (rfree + value)
Selected AbstractsStructure of a monoclinic polymorph of human carbonic anhydrase II with a doubled a axisACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010Arthur H. Robbins The crystal structure of human carbonic anhydrase II with a doubled a axis from that of the usually observed monoclinic unit cell has been determined and refined to 1.4,Å resolution. The diffraction data with h = 2n + 1 were systematically weaker than those with h = 2n. Consequently, the scaling of the data, structure solution and refinement were challenging. The two molecules comprising the asymmetric unit are related by a noncrystallographic translation of ½ along a, but one of the molecules has two alternate positions related by a rotation of approximately 2°. This rotation axis is located near the edge of the central ,-sheet, causing a maximum distance disparity of 1.7,Å between equivalent atoms on the diametrically opposite side of the molecule. The crystal-packing contacts are similar to two sequential combined unit cells along a of the previously determined monoclinic unit cell. Abnormally high final Rcryst and Rfree values (20.2% and 23.7%, respectively) are not unusual for structures containing pseudo-translational symmetry and probably result from poor signal to noise in the weak h -odd data. [source] Structure of the isoaspartyl peptidase with l -asparaginase activity from Escherichia coliACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2004Adam Prahl The crystal structure of the Escherichia coli enzyme (EcAIII) with isoaspartyl dipeptidase and l -asparaginase activity has been solved and refined to a resolution of 1.65,Å, with crystallographic R -factor and Rfree values of 0.178 and 0.209, respectively. EcAIII belongs to the family of N-terminal hydrolases. The amino-acid sequence of EcAIII is homologous to those of putative asparaginases from plants. The structure of EcAIII is similar to the structures of glycosylasparaginases. The mature and catalytically active form of EcAIII is a heterotetramer consisting of two ,-subunits and two ,-subunits. Both of the equivalent active sites present in the EcAIII tetramer is assisted by a metal-binding site. The metal cations, modelled here as Na+, have not previously been observed in glycosylasparaginases. This reported structure helps to explain the inability of EcAIII and other plant-type asparaginases to hydrolyze N4 -(,- N -acetylglucosaminyl)- l -asparagine, the substrate of glycosylasparaginases. [source] Near-atomic resolution crystal structure of an A-DNA decamer d(CCCGATCGGG): cobalt hexammine interaction with A-DNAACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2003Boopathy Ramakrishnan The structure of the DNA decamer d(CCCGATCGGG) has been determined at 1.25,Å resolution. The decamer crystallized in the tetragonal space group P43212, with unit-cell parameters a = b = 44.3, c = 24.8,Å and one strand in the asymmetric unit. The structure was solved by the molecular-replacement method and refined to Rwork and Rfree values of 16.3 and 18.5%, respectively, for 5969 reflections. The decamer forms the A-form DNA duplex, with the abutting crystal packing typical of A-DNA. The crystal packing interactions seem to distort the local conformation: A5 adopts the trans/trans conformation for the torsion angles , and , instead of the usual gauche,/gauche+ conformations, yielding G*(G·C) base triplets. The highly hydrated [Co(NH3)6]3+ ion adopts a novel binding mode to the DNA duplex, binding directly to phosphate groups and connecting to N7 and O6 atoms of guanines by water bridges. Analysis of thermal parameters (B factors) shows that the nucleotides involved in abutting crystal packing are thermally more stable than other nucleotides in the duplex. [source] The 1.4,Å resolution structure of Paracoccus pantotrophus pseudoazurinACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2010Shabir Najmudin Pseudoazurins are small type 1 copper proteins that are involved in the flow of electrons between various electron donors and acceptors in the bacterial periplasm, mostly under denitrifying conditions. The previously determined structure of Paracoccus pantotrophus pseudoazurin in the oxidized form was improved to a nominal resolution of 1.4,Å, with R and Rfree values of 0.188 and 0.206, respectively. This high-resolution structure makes it possible to analyze the interactions between the monomers and the solvent structure in detail. Analysis of the high-resolution structure revealed the structural regions that are responsible for monomer,monomer recognition during dimer formation and for protein,protein interaction and that are important for partner recognition. The pseudoazurin structure was compared with other structures of various type 1 copper proteins and these were grouped into families according to similarities in their secondary structure; this may be useful in the annotation of copper proteins in newly sequenced genomes and in the identification of novel copper proteins. [source] Structure of the T109S mutant of Escherichia coli dihydroorotase complexed with the inhibitor 5-fluoroorotate: catalytic activity is reflected by the crystal formACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2007Mihwa Lee Crystals of a single-point mutant (T109S) of Escherichia coli dihydroorotase (DHOase) with diminished activity grown in the presence of l -dihydroorotate (l -DHO) are tetragonal, with a monomer in the asymmetric unit. These crystals are extremely unstable and disintegrate shortly after formation, which is followed by the growth of orthorhombic crystals from the remnants of the tetragonal crystals or at new nucleation sites. Orthorhombic crystals, for which a structure has previously been reported [Thoden et al. (2001), Biochemistry, 40, 6989,6997; Lee et al. (2005), J. Mol. Biol.348, 523,533], contain a dimer of DHOase in the asymmetric unit; the active site of one monomer contains the substrate N -carbamyl- l -aspartate (l -CA-asp) and the active site of the other monomer contains the product of the reaction, l -DHO. In the subunit with l -DHO in the active site, a surface loop (residues 105,115) is `open'. In the other subunit, with l -CA-asp in the active site, the loop folds inwards, forming specific hydrogen bonds from the loop to the l -CA-asp. The tetragonal crystal form can be stabilized by crystallization in the presence of the inhibitor 5-fluoroorotate (FOA), a product (l -DHO) mimic. Crystals of the complex of T109S DHOase with FOA are tetragonal, space group P41212, with unit-cell parameters a = b = 72.6, c = 176.1,Å. The structure has been refined to R and Rfree values of 0.218 and 0.257, despite severe anisotropy of the diffraction. In this structure, the flexible loops are both in the `open' conformation, which is consistent with FOA, like l -DHO, binding at both sites. The behaviour of the T109S mutant crystals of DHOase in the presence of l -DHO is explained by initial binding of l -DHO to both subunits, followed by slow conversion to l -CA-asp, with consequent movement of the flexible loop and dissolution of the crystals. Orthorhombic crystals are then able to grow in the presence of l -DHO and l -CA-asp. [source] Monellin (MNEI) at 1.15,Å resolutionACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2007J. R. Hobbs The X-ray crystal structure of a single-chain monellin protein (MNEI) has been determined at 1.15,Å resolution. The model was refined to convergence employing anisotropic displacement parameters and riding H atoms to produce a final model with Rwork and Rfree values of 0.132 and 0.162, respectively. The crystal contains a single MNEI protein in the asymmetric unit and unusually lacks the dimer interface observed in all previous crystal structures of monellin and its single-chain derivatives. The high resolution allowed a more detailed view of MNEI than previously possible, with 38 of the 96 residues modelled with alternative side-chain conformations, including four core residues Thr12, Cys41, Leu62 and Ile75. Four stably bound negative ions were also located, providing new insight into potential electrostatic interactions of MNEI with the largely negatively charged surface of the sweet taste receptor T1R2,T1R3. [source] | ||||||||||