Two crystal forms of the lentil lectin diffract to high resolution.

The legume lectins are an important class of polysaccharide-binding proteins with a wide range of biochemical and immunological applications. Two high-resolution crystal forms are obtained for the lentil (Lens culinaris) lectin: a monoclinic P21 and an orthorhombic P212121. The unit cell dimensions for the monoclinic form are a = 58.0 A, b = 56.0 A, c = 82.1 A, beta = 104.4 degrees, while for the orthorhombic form a = 56.4 A, b = 74.6 A, c = 124.9 A. The asymmetric unit contains one dimer in both cases. The crystals diffract to 1.7 A resolution using synchrotron radiation. Preliminary data have been collected to 2.3 A on both crystal forms using a conventional X-ray source.

A comparative structural study on the steroids [1,2,5]oxadiazolo[3', 4':3,4]-5 alpha-pregn-16-en-20-one oxime (HS998), [1,2,5]oxadiazolo[3, 4':3,4]-5 beta-pregn-16-en-20-one (HS973) by NMR, molecular modeling, and X-ray investigations.

The molecular structure of the steroids [1,2,5]oxadiazolo[3', 4':3,4]-5 alpha-pregn-16-en-20-one oxime, [1,2,5]oxadiazolo[3',4':3, 4':3,4]-5 alpha-pregn-16-en-20-one and [1,2,5]oxadiazole]3',4':3,4]-5 beta-pregn-16-en-20-one has been determined. The proton-proton distances in the solid state from previous crystallographic studies are compared with the corresponding distances from novel and previous solution NMR as well as from novel in vacuo modeling studies.

A new antiplasmodial coumarin from Toddalia asiatica roots.

A new antiplasmodial coumarin, 5,7-dimethoxy-8-(3'-hydroxy-3'methyl-1'-butene)-coumarin (1), has been isolated from the roots of Toddalia asiatica. This finding supports the traditional use of this plant for the treatment of malaria.

The structure of stiripentol: 4,4 dimethyl- 1-(3,4-methylenedioxyphenyl)-1-penten-3-ol-a novel antiepileptic drug.

C14H18O3, Mr = 234.29, monoclinic, P2(1)/a, a = 14.550 (8), b = 6.133 (4), c = 15.703 (7) A, beta = 116.1 (4) degree, V = 1254.4 (5) A3, Z = 4, Dm = 1.24 (4), Dx = 1.239 g cm-3, lambda (Cu K alpha) = 1.54184 A, mu = 6.15 cm-1, F(000) = 504, room temperature, R = 0.065 for 2426 observed reflections. The five-membered ring A has an envelope conformation, the apical atom C(7)* being out of the plane. The conformation of the side chain attached to C(1)* is almost fully extended. The molecules are packed in a head-to-tail fashion as hydrogen-bonded dimers: O(3)...O(4)* [1-x, y, 1-z] = 3.124 (8), HO(3)...O(4)* = 2.19 (9) A, O(3)-HO(8)...O(4)* V 160.2 (6) degree.

The structure of (1,2-benzisoxazol-3-yl)methanesulfonamide: a novel antiepileptic drug.

C8H8N2O3S, Mr = 212.54, monoclinic, P2(1)/a, a = 7.347 (9), b = 13.237 (4), c = 10.128 (8) A, beta = 108.916 (6) degree, V = 931.9 (1) A3, Z = 4, Dm = 1.52 (4), Dx = 1.514 g cm-3, lambda (Cu K alpha) = 1.54184 A, mu = 28.35 cm-1, F(000) = 440, room temperature, R = 0.040 for 1864 observed reflections. The sulfonamide N forms intermolecular hydrogen bonds with the benzisoxazole ring N and also with the O on the sulfonamide group. Centrosymmetrically related benzisoxazole ring pairs are pi bonded with a high degree of overlap.

Purification, crystallization, and preliminary X-ray studies on the rhizome lectin from stinging nettle and its complex with NN'N"-triacetylchitotriose.

Single crystals were grown from affinity-purified stinging nettle lectin and from its complex with the specific trisaccharide NN'N"-triacetylchitotriose by vapor diffusion at room temperature. The lectin crystallizes in space group P2(1)2(1)2(1) with unit cell dimensions a = 54.3 (1) A, b = 62.2 (1) A, and c = 92.4 (2) A, and diffracts to 3.0 A resolution. The asymmetric unit contains three lectin monomers. The crystals of the lectin-trisaccharide complex have space group P2(1)2(1)2(1) with cell constants a = 37.69 (4) A, b = 48.97 (6) A, and c = 57.32 (4) A. These crystals diffract to at least 2.0 A resolution and the asymmetric unit contains one lectin monomer. A three-dimensional X-ray structure determination is on its way.

Crystallization and preliminary X-ray analysis of the DNA decamers d(CCGGATCCGG) and d(CCGGCGCCGG).

The DNA decamers d(CCGGATCCGG) and d(CCGGCGCCGG) have been crystallized for X-ray analysis in order to investigate the effects of changing the two central base pairs of the DNA fragment d(CCGGGACCGG). Previous studies have already demonstrated that the structure of the former DNA fragment contains a DNA Holliday junction. Crystals were obtained at 293 K by the hanging-drop vapour-diffusion technique using the Nucleic Acid Mini Screen. Over a period of two weeks, hexagonal plates appeared. For the DNA fragment d(CCGGATCCGG), the crystals belong to space group P3(1), with unit-cell parameters a = b = 33.54, c = 46.39 A, alpha = beta = 90, gamma = 120 degrees, and diffract to 2.2 A. In the case of the DNA fragment d(CCGGCGCCGG) the crystals belong to the space group C2, with unit-cell parameters a = 65.35, b = 24.07, c = 37.34 A, beta = 109.97 degrees, and diffract to 2.0 A.

Crystal structure determination and refinement at 2.3-A resolution of the lentil lectin.

We report on the X-ray structure determination of the orthorhombic crystal form of lentil lectin by molecular replacement using the pea lectin coordinates as a starting model. The structure was refined at 2.3-A resolution with a combination of molecular dynamics refinement and classical restrained least-squares refinement. The final R value for all data Fo > 1 sigma (Fo) between 7.0- and 2.3-A resolution is 0.164%, and deviations from ideal bond distances are 0.014 A. The C-terminus of the beta-chain proved to be 23 amino acids longer than found in previous studies. This together with several inconsistencies between the previously determined amino acid sequence and the observed electron density forced a redetermination of the amino acid sequence of the protein. The overall structure is very similar to that of pea lectin and isolectin I of Lathyrus ochrus, the most prominent deviations being confined to loop regions and the regions of intermolecular contact. The largest difference between the pea and lentil lectin monomers is situated in the loop region of amino acids 73-79 of the beta chain. There are no significant differences between the two crystallographic independent lentil lectin monomers in the asymmetric unit. The model includes 104 well-defined water molecules, of which a significant number have a counterpart in the pea lectin structure. As for the other legume lectins, each lentil lectin monomer contains one calcium ion in a highly conserved environment. On the contrary, the manganese binding sites are distorted with respect to the pea lectin and concanavalin A structures. The Asp beta 121 side chain apparently does not ligate the Mn2+ ion. This difference is consistent in both lentil lectin monomers and agrees with earlier solution studies. Possible implications for oligosaccharide binding are discussed.

Crystallization of Pleurotus ostreatus (oyster mushroom) lectin.

Crystals of Pleurotus ostreatus (oyster mushroom) lectin have been grown by the hanging-drop technique using ammonium sulfate as the precipitant at 293 K. Over a period of between two and three weeks, crystals of hexagonal bipyramidal morphology grew to maximum dimensions of 0.2 x 0.2 x 0.5 mm. The crystals belong to space group P6(1)22 or P6(5)22, with unit-cell parameters a = b = 155.9, c = 149. 8 A, V = 3153078 A(3), Z = 12 (assuming 50% solvent), and diffract to 4.1 A at 293 K.

Crystallization and preliminary X-ray analysis of the antimalarial and cytotoxic alkaloid cryptolepine complexed with the DNA fragment d(CCTAGG)2.

Crystals of the indoloquinoline alkaloid cryptolepine complexed with the DNA fragment d(CCTAGG)(2) have been grown by the hanging-drop technique at 293 K using ammonium sulfate as the precipitating agent. Over a period of three weeks, yellow tapering bullet-shaped crystals grew to maximum dimensions of 0.2 x 0.1 x 0.1 mm. The crystals belong to space group P6(4), with unit-cell parameters a = b = 29.960, c = 39.64 A, alpha = beta = 90, gamma = 120 degrees, and diffract to 1.4 A.

Structure of the crystalline complex of cytidylic acid (2'-CMP) with ribonuclease at 1.6 A resolution. Conservation of solvent sites in RNase-A high-resolution structures.

The X-ray structure of the inhibitor complex of bovine ribonuclease A with cytidylic acid (2'-CMP) has been determined at 1.6 A resolution and refined by restrained least squares to R = 0.17 for 11 945 reflections. Binding of the inhibitor molecule to the protein is confirmed to be in the productive mode associated with enzyme activity. A study of conserved solvent sites amongst high-resolution structures in the same crystal form reveals a stabilizing water cluster between the N and C termini.

Crystallization of Helix pomatia agglutinin (HPA), a protein from the edible snail.

Crystals of Helix pomatia agglutinin (HPA) have been grown by the hanging-drop technique using polyethylene glycol as the precipitant at 293 K. Over a period of one to two weeks the crystals grew to maximum dimensions of 0.10 x 0.05 x 0.02 mm. The crystals belong to space group P6(3)22, with unit-cell dimensions a = b = 63.3, c = 105. 2 A and Z = 12 identical monomers of M(r) = 13 kDa, aggregating into two 78 kDa hexameric protein molecules per unit cell, each with symmetry 32 (D(3)). The diffraction pattern extends to 3.6 A at 293 K.

X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection.

The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol, C(24)H(30)O(6).H(2)O (1), code name P326, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and in both cases the crystals exhibit P2(1) symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P2(1)/c. The higher symmetry is broken mainly by the two independent water molecules in the unit cell, some reflections which would be absent in P2(1)/c having strong intensities in both the X-ray and neutron data. In both molecules A and B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contacts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the molecular plane and through atoms C(9) and O(18), and in addition are predominantly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refinement in the neutron analysis.