Amine free crystal structure: the crystal structure of d(CGCGCG)2 and methylamine complex crystal

We succeeded in the crystallization of d(CGCGCG)2 and methylamine Complex. The crystal was clear and of sufficient size to collect the X-ray crystallographic data up to 1.0 A resolution using synchrotron radiation. As a result of X-ray crystallographic analysis of 2Fo-Fc map was much clear and easily traced. It is the first time monoamine co-crystallizes with d(CGCGCG)2. However, methylamine was not found from the complex crystal of d(CGCGCG)2 and methylamine. Five Mg ions were found around d(CGCGCG)2 molecules. These Mg ions neutralized the anion of 10 values of the phosphate group of DNA with five Mg2+. DNA stabilized only by a metallic ion and there is no example of analyzing the X-ray crystal structure like this. Mg ion stabilizes the conformation of Z-DNA. To use monoamine for crystallization of DNA, we found that we can get only d(CGCGCG)2 and Mg cation crystal. Only Mg cation can stabilize the conformation of Z-DNA. The method of using the monoamine for the crystallization of DNA can be applied to the crystallization of DNA of long chain of length in the future like this.     

Solution structure of the loops of bacteriorhodopsin closely resembles the crystal structure

Bacteriorhodopsin is one of very few transmembrane proteins for which high resolution structures have been solved. The structure shows a bundle of seven helices connected by six turns. Some turns in proteins are stabilized by short range interactions and can behave as small domains. These observations suggest that peptides containing the sequence of the turns in a membrane protein such as bacteriorhodopsin may form stable turn structures in solution. To test this hypothesis, we determined the solution structure of three peptides each containing the sequence of one of the turns in bacteriorhodopsin. The solution structures of the peptides closely resemble the structures of the corresponding turns in the high resolution structures of the intact protein.     

Exhaustive crystal structure search and crystal modeling of beta-chitin

An exhaustive search of the crystal structure of beta-chitin was carried out by simultaneously optimizing all the structural parameters based on published X-ray diffraction data and stereochemical criteria. The most probable structure was characterized by a parallel-up chain polarity, a gg orientation of hydroxymethyl groups and an intermolecular hydrogen bond along the a-axis, which essentially reproduced the original structure proposed by Gardner and Blackwell. The proposed crystal structure was subsequently subjected to crystal modeling using the AMBER force field. The probable orientation of hydroxyl groups and their motional behaviors is proposed based on calculations for the crystal models identified. Solvated crystal models exhibited a slightly deformed structure with the formation of appreciable numbers of hydrogen bonds along the b-axis.     

The crystal structure of L-chiro-inositol

The crystal structure of L-chiro-inositol is monoclinic, P21, with a = 6.867(3), b = 9.133(4), c = 6.217(3) A, beta = 106.59(4) degrees, Z = 2. The structure was solved by using MULTAN, and refined to R = 0.028 for 1065 intensities observed with Ni-filtered MoK alpha radiation. The molecule has the expected chair conformation, with puckering parameters Q = 0.561 A, theta = 4.4 degrees, phi = 51.2 degrees. The non-hydrogen molecular symmetry is close to C2, with deviations of less than 0.07 A from a weighted fit. The intramolecular hydrogen-bonding forms infinite chains which are cross-linked through the weaker component of a three-center bond. The C-C bond lengths range from 1.515 to 1.528 A, and the C-O bond lengths from 1.418 to 1.436 A. The C-C-C angles range from 109.7 to 113.1 degrees, and the C-C-O angles from 106.5 to 112.0 degrees.     

Serpin crystal structure and serpin polymer structure

Serpins are a family of structurally homologous proteins having metastable native structures. As a result, a serpin variant destabilized by mutation(s) has a tendency to undergo conformational changes leading to inactive forms, e.g., the latent form and polymer. Serpin polymers are involved in a number of conformational diseases. Although several models for polymer structure have been proposed, the actual structure remains unknown. Here, we provide a comprehensive list of serpins, both free and in complexes, deposited in the Protein Data Bank. Our discussion focuses on structures that potentially can contribute to a better understanding of polymer structure.     

Atomic-resolution crystal structure of the antiviral lectin scytovirin

The crystal structures of the natural and recombinant antiviral lectin scytovirin (SVN) were solved by single-wavelength anomalous scattering and refined with data extending to 1.3 A and 1.0 A resolution, respectively. A molecule of SVN consists of a single chain 95 amino acids long, with an almost perfect sequence repeat that creates two very similar domains (RMS deviation 0.25 A for 40 pairs of Calpha atoms). The crystal structure differs significantly from a previously published NMR structure of the same protein, with the RMS deviations calculated separately for the N- and C-terminal domains of 5.3 A and 3.7 A, respectively, and a very different relationship between the two domains. In addition, the disulfide bonding pattern of the crystal structures differs from that described in the previously published mass spectrometry and NMR studies.     

Survivin structure: crystal unclear

The recent X-ray structures of the anti-apoptotic protein survivin reveal two different dimeric interfaces. More experiments are needed to determine the biologically relevant dimer interface and to probe survivin function on the basis of its structure.     

The crystal structure of rabbit IgG-Fc

We report the structure of the Fc fragment of rabbit IgG at 1.95 A (1 A=0.1 nm) resolution. Rabbit IgG was the molecule for which Porter established the four-chain, Upsilon-shaped structure of the antibody molecule, and crystals of the Fc ('Fragment crystallisable') were first reported almost 50 years ago in this journal [Porter, R. R. (1959) Biochem. J. 73, 119-126]. This high-resolution analysis, apparently of the same crystal form, reveals several features of IgG-Fc structure that have not previously been described. More of the lower hinge region is visible in this structure than in others, demonstrating not only the acute bend in the IgG molecule that this region can mediate, as seen in receptor complexes, but also that this region has a tendency to adopt a bent structure even in the absence of receptor. As observed in other IgG-Fc structures, the Cgamma2 domains display greater mobility/disorder within the crystals than the Cgamma3 domains; unexpectedly the structure reveals partial cleavage of both Cgamma2 intra-domain disulphide bonds, whereas an alternative conformation for one of the cysteine residues in the intact bridge within the more ordered Cgamma3 domains is observed. The N-linked oligosaccharide chains at Asn(297) are well-defined and reveal two alternative conformations for the galactose units on each of the alpha(1-6)-linked branches. The presence of this galactose unit is important for stabilizing the structure of the entire branched carbohydrate chain, and its absence correlates with the severity of autoimmune conditions such as rheumatoid arthritis in both human clinical studies and in a rabbit model of the disease. Rabbit IgG, through this high-resolution structure of its Fc region, thus continues to offer new insights into antibody structure.     

The crystal structure of Afc-containing peptides

A systematic structural analysis of Afc (9-amino-fluorene-9-carboxylic acid) containing peptides is here reported. The crystal structures of four fully protected tripeptides containing the Afc residue in position 2: Z-X(1)-Afc(2)-Y(3)-OMe (peptide a: X = Y = Gly; peptide b: X = Aib, C(alpha, alpha)-dimethylglycine, Y = Gly; peptide c: X = Gly, Y = Aib; peptide d: X = Y = Aib) have been solved by x-ray crystallography. All the results suggest that the Afc residue has a high propensity to assume an extended conformation. In fact, the Afc residue adopts an extended conformation in three peptides examined in this paper (peptides a-c). In contrast, Afc was found in a folded conformation, in the 3(10)-helical region, only in the peptide d, in which it is both preceded and followed by the strong helix promoting Aib.     

The crystal structure of UUCG tetraloop

All large structured RNAs contain hairpin motifs made of a stem closed by several looped nucleotides. The most frequent loop motif is the UUCG one. This motif belongs to the tetraloop family and has the peculiarity of being highly thermodynamically stable. Here, we report the first crystal structure of two UUCG tetraloops embedded in a larger RNA-protein complex solved at 2.8 A resolution. The two loops present in the asymmetric unit are in a different crystal packing environment but, nevertheless, have an identical conformation. The observed structure is globally close to that obtained in solution by nuclear magnetic resonance. However, subtle differences point to a more detailed picture of the role played by 2'-hydroxyl groups in stabilising this tetraloop.     

The crystal structure of uncomplexed-hydrated cyclooctaamylose

Cyclooctaamylose crystallizes from aqueous solution with space-group symmetry P2₁ and lattice parameters: $\text{a}\text{= 20.253(8),}\text{b}\text{= 10.494(5),}\text{c}\text{= 16.892(6)}$ A and β = 105.32(1)^o, Z = 2; the apparent formular per asymmetric unit is C₄₈H₈₀O₄₀·17H₂O. The macrocycle is in an open conformation but displays significant deviations from ideal eight fold molecular symmetry. Of the 19 water molecules thus far located, four of which have occupancy factors of one half, 12 may be characterized as being in the torus of the cycloamylose.     

Refined crystal structure of deoxyhemoglobin S. II. Molecular interactions in the crystal

The refined crystal structure of deoxyhemoglobin S (Padlan, E. A., and Love, W. E. (1985) J. Biol. Chem. 260, 8272-8279) was used to analyze in detail the molecular interactions between hemoglobin tetramers in the crystal. The analysis confirms the close similarity and also the nonequivalence of the molecular interactions involving the two independent tetramers in the asymmetric unit of the crystal. The residue at the site of the hemoglobin S mutation, beta 6, is intimately involved in the lateral contacts between adjacent molecules. The molecular contacts in the crystals of deoxyhemoglobin S, deoxyhemoglobin A, and deoxyhemoglobin F were compared; some contacts involve the same regions of the molecule although the details of the interactions are very different. The effect of introducing an R state tetramer into the deoxyhemoglobin S strands was investigated using the known structure of carbon monoxyhemoglobin A. It was found that substituting a molecule of carbon monoxyhemoglobin A for one of the deoxyhemoglobin S tetramers results in extensive molecular interpenetration.     

The crystal structure of cholesteryl octanoate

Crystals of cholesteryl octanoate (C₃₅H₆₀O₂) are monoclinic, space group P2₁, with $\text{a = 12.80(3), b = 9.20(2), c = 14.12(3)}\text{A}\text{?}$, β = 93.81(3)° and 2 molecules per unit cell. The structure has been determined by Patterson rotation and translation methods from the X-ray intensities (Mo-Kα radiation) of 1320 reflections ($\text{sin}\text{θ/λ < 0.59}\text{A}\text{?}{}^{\mathrm{?1}}$) measured with a diffractometer. Refinement by block diagonal least squares and Fourier methods gave R = 0.096. The molecules are arranged in monolayers with their long axes antiparallel and severely tilted (28°). There is a close packing of cholesteryls within the monolayers, but the octanoate chains which form the layer interface regions are conformationally and thermally disordered. The crystal structure is quite different from that of cholesteryl nonanoate, as expected from the discontinuity in thermodynamic properties and phase behaviour which occurs at this point in the homologous series.     

The crystal structure of the potassium salt of nigericin

The molecular structure of the potassium salt of the ionophorous antibiotic nigericin has been determined by single crystal X-ray crystallography. The structure is almost isomorphous with that of the silver salt but the accommodation of the slightly larger potassium ion has resulted in a number of significant changes in torsional angles. The metal-ligand distances are generally somewhat larger in the potassium salt than in the silver salt even after allowance is made for differences in ionic radii, and this is particularly marked in the case of the metal-carboxyl oxygen distance.     

2.8 A crystal structure of the malachite green aptamer

Previous in vitro selection experiments identified an RNA aptamer that recognizes the chromophore malachite green (MG) with a high level of affinity, and which undergoes site-specific cleavage following laser irradiation. To understand the mechanism by which this RNA folds to recognize specifically its ligand and the structural basis for chromophore-assisted laser inactivation, we have determined the 2.8 A crystal structure of the aptamer bound to tetramethylrosamine (TMR), a high-affinity MG analog. The ligand-binding site is defined by an asymmetric internal loop, flanked by a pair of helices. A U-turn and several non-canonical base interactions stabilize the folding of loop nucleotides around the TMR. The aptamer utilizes several tiers of stacked nucleotides arranged in pairs, triples, and a novel base quadruple to effectively encapsulate the ligand. Even in the absence of specific stabilizing hydrogen bonds, discrimination between related fluorophores and chromophores is possible due to tight packing in the RNA binding pocket, which severely limits the size and shape of recognized ligands. The site of laser-induced cleavage lies relatively far from the bound TMR ( approximately 15 A). The unusual backbone conformation of the cleavage site nucleotide and its high level of solvent accessibility may combine to allow preferential reaction with freely diffusing hydroxyl radicals generated at the bound ligand. Several observations, however, favor alternative mechanisms for cleavage, such as conformational changes in the aptamer or long-range electron transfer between the bound ligand and the cleavage site nucleotide.     

Refined crystal structure of the phosphorylase-heptulose 2-phosphate-oligosaccharide-AMP complex

The crystal structure of phosphorylase b-heptulose 2-phosphate complex with oligosaccharide and AMP bound has been refined by molecular dynamics and crystallographic least-squares with the program XPLOR. Shifts in atomic positions of up to 4 A from the native enzyme structure were correctly determined by the program without manual intervention. The final crystallographic R value for data between 8 and 2.86 A resolution is 0.201, and the overall root-mean-square difference between the native and complexed structure is 0.58 A for all protein atoms. The results confirm the previous observation that there is a direct hydrogen bond between the phosphate of heptulose 2-phosphate and the pyridoxal phosphate 5'-phosphate group. The close proximity of the two phosphates is stabilized by an arginine residue, Arg569, which shifts from a site buried in the protein to a position where it can make contact with the product phosphate. There is a mutual interchange in position between the arginine and an acidic group, Asp283. These movements represent the first stage of the allosteric response which converts the catalytic site from a low to a high-affinity binding site. Communication of these changes to other sites is prevented in the crystal by the lattice forces, which also form the subunit interface. The constellation of groups in the phosphorylase transition state analogue complex provides a structural basis for understanding the catalytic mechanism in which the cofactor pyridoxal phosphate 5'-phosphate group functions as a general acid to promote attack by the substrate phosphate on the glycosidic bond when the reaction proceeds in the direction of glycogen degradation. In the direction of glycogen synthesis, stereoelectronic effects contribute to the cleavage of the C-1-O-1 bond. In both reactions the substrate phosphate plays a key role in transition state stabilization. The details of the oligosaccharide, maltoheptaose, interactions with the enzyme at the glycogen storage site are also described.