Ultra-high resolution X-ray structure of orthorhombic bovine pancreatic Ribonuclease A at 100K

The crystal structure of orthorhombic Bovine Pancreatic Ribonuclease A has been determined to 0.85 Å resolution using low temperature, 100 K, synchrotron X-ray data collected at 16000 keV (λ = 0.77 Å). This is the first ultra-high-resolution structure of a native form of Ribonuclease A to be reported. Refinement carried out with anisotropic displacement parameters, stereochemical restraints, inclusion of H atoms in calculated positions, five [Formula: see text] moieties, eleven ethanol molecules and 293 water molecules, converged with final R values of R1(Free) = 0.129 (4279 reflections) and R1 = 0.112 (85,346 reflections). The refined structure was deposited in the Protein Data Bank as structure 7p4r. Conserved waters, using four high resolution structures, have been investigated. Cluster analysis identified clusters of water molecules that are associated with the active site of Bovine Ribonuclease A. Particular attention has been paid to making detailed comparisons between the present structure and other high quality Bovine Pancreatic Ribonuclease A X-ray crystal structures with special reference to the deposited classic monoclinic structure 3RN3 Howlin et al. (Acta Crystallogr A 45:851-861, 1989). Detailed studies of various aspects of hydrogen bonding and conformation have been carried out with particular reference to active site residues Lys-1, Lys-7, Gln-11, His-12, Lys-41, Asn-44, Thr-45, Lys-66, His-119 and Ser-123. For the two histidine residues in the active site the initial electron density map gives a clear confirmation that the position of His-12 is very similar in the orthorhombic structure to that in 3RN3. In 3RN3 His-119 exhibited poor electron density which was modelled and refined as two distinct sites, A (65%) and B (35%) but with respect to His-119 in the present ultra-high resolution orthorhombic structure there is clear electron density which was modelled and refined as a single conformation distinct from either conformation A or B in 3RN3. Other points of interest include Serine-32 which is disordered at the end of the sidechain in the present orthorhombic form but has been modelled as a single form in 3RN3. Lysine-66: there is density indicating a possible conformation for this residue. However, the density is relatively weak, and the conformation is unclear. Three types of amino acid representation in the ultra-high resolution electron density are examined: (i) sharp with very clearly resolved features, for example Lys-37; (ii) well resolved but clearly divided into two conformations which are well behaved in the refinement, both having high quality geometry, for example Tyr-76; (iii) poor density and difficult or impossible to model, an example is Lys-31 for which density is missing except for Cβ. The side chains of Gln-11, His-12, Lys-41, Thr-45 and His-119 are generally recognised as being closely involved in the enzyme activity. It has also been suggested that Lys-7, Asp-44, Lys-66, Phe-120, Asp-121 and Ser-123 may also have possible roles in this mechanism. A molecular dynamics study on both structures has investigated the conformations of His-119 which was modelled as two conformations in 3RN3 but is observed to have a single clearly defined conformation in the present orthorhombic structure. MD has also been used to investigate Lys-31, Lys-41 and Ser32. The form of the Ribonuclease A enzyme used in both the present study and in 3RN3 (Howlin et al. in Acta Crystallogr A 45:851-861, 1989) includes a sulphate anion which occupies approximately the same location as the [Formula: see text] phosphate group in protein nucleotide complexes (Borkakoti et al. in J Mol Biol 169:743-755, 1983). The present structure contains 5 [Formula: see text] groups SO41151-SO41155 two of which, SO41152 and SO41153 are disordered, SO41152 being in the active site, and 11 EtOH molecules, EOH A 201-EOH A 211 all of which have good geometry. H atoms were built into the EtOH molecules geometrically. Illustrations of these features in the present structure are included here. The sulphates are presumably present in the material purchased for use in the present study. 293 water molecules are included in the present structure compared to 134 in 3RN3 (Howlin et al. in Acta Crystallogr A 45:851-861, 1989).

Semi-Synthetic Analogues of Cryptolepine as a Potential Source of Sustainable Drugs for the Treatment of Malaria, Human African Trypanosomiasis, and Cancer

The prospect of eradicating malaria continues to be challenging in the face of increasing parasite resistance to antimalarial drugs so that novel antimalarials active against asexual, sexual, and liver-stage malaria parasites are urgently needed. In addition, new antimalarials need to be affordable and available to those most in need and, bearing in mind climate change, should ideally be sustainable. The West African climbing shrub Cryptolepis sanguinolenta is used traditionally for the treatment of malaria; its principal alkaloid, cryptolepine (1), has been shown to have antimalarial properties, and the synthetic analogue 2,7-dibromocryptolepine (2) is of interest as a lead toward new antimalarial agents. Cryptolepine (1) was isolated using a two-step Soxhlet extraction of C. sanguinolenta roots, followed by crystallization (yield 0.8% calculated as a base with respect to the dried roots). Semi-synthetic 7-bromo- (3), 7, 9-dibromo- (4), 7-iodo- (5), and 7, 9-dibromocryptolepine (6) were obtained in excellent yields by reaction of 1 with N-bromo- or N-iodosuccinimide in trifluoroacetic acid as a solvent. All compounds were active against Plasmodia in vitro, but 6 showed the most selective profile with respect to Hep G2 cells: P. falciparum (chloroquine-resistant strain K1), IC₅₀ = 0.25 µM, SI = 113; late stage, gametocytes, IC₅₀ = 2.2 µM, SI = 13; liver stage, P. berghei sporozoites IC₅₀ = 6.13 µM, SI = 4.6. Compounds 3-6 were also active against the emerging zoonotic species P. knowlesi with 5 being the most potent (IC₅₀ = 0.11 µM). In addition, 3-6 potently inhibited T. brucei in vitro at nM concentrations and good selectivity with 6 again being the most selective (IC₅₀ = 59 nM, SI = 478). These compounds were also cytotoxic to wild-type ovarian cancer cells as well as adriamycin-resistant and, except for 5, cisplatin-resistant ovarian cancer cells. In an acute oral toxicity test in mice, 3-6 did not exhibit toxic effects at doses of up to 100 mg/kg/dose × 3 consecutive days. This study demonstrates that C. sanguinolenta may be utilized as a sustainable source of novel compounds that may lead to the development of novel agents for the treatment of malaria, African trypanosomiasis, and cancer.

Specific refolding pathway of viscumin A chain in membrane-like medium reveals a possible mechanism of toxin entry into cell

How is a water-soluble globular protein able to spontaneously cross a cellular membrane? It is commonly accepted that it undergoes significant structural rearrangements on the lipid-water interface, thus acquiring membrane binding and penetration ability. In this study molecular dynamics (MD) simulations have been used to explore large-scale conformational changes of the globular viscumin A chain in a complex environment – comprising urea and chloroform/methanol (CHCl₃/MeOH) mixture. Being well-packed in aqueous solution, viscumin A undergoes global structural rearrangements in both organic media. In urea, the protein is “swelling” and gradually loses its long-distance contacts, thus resembling the “molten globule” state. In CHCl₃/MeOH, viscumin A is in effect turned “inside out”. This is accompanied with strengthening of the secondary structure and surface exposure of hydrophobic epitopes originally buried inside the globule. Resulting solvent-adapted models were further subjected to Monte Carlo simulations with an implicit hydrophobic slab membrane. In contrast to only a few point surface contacts in water and two short regions with weak protein-lipid interactions in urea, MD-derived structures in CHCl₃/MeOH reveal multiple determinants of membrane interaction. Consequently it is now possible to propose a specific pathway for the structural adaptation of viscumin A with respect to the cell membrane – a probable first step of its translocation into cytoplasmic targets.

Ultra-high resolution X-ray structures of two forms of human recombinant insulin at 100 K

The crystal structure of a commercially available form of human recombinant (HR) insulin, Insugen (I), used in the treatment of diabetes has been determined to 0.92 Å resolution using low temperature, 100 K, synchrotron X-ray data collected at 16,000 keV (λ = 0.77 Å). Refinement carried out with anisotropic displacement parameters, removal of main-chain stereochemical restraints, inclusion of H atoms in calculated positions, and 220 water molecules, converged to a final value of R = 0.1112 and R_free = 0.1466. The structure includes what is thought to be an ordered propanol molecule (POL) only in chain D(4) and a solvated acetate molecule (ACT) coordinated to the Zn atom only in chain B(2). Possible origins and consequences of the propanol and acetate molecules are discussed. Three types of amino acid representation in the electron density are examined in detail: (i) sharp with very clearly resolved features; (ii) well resolved but clearly divided into two conformations which are well behaved in the refinement, both having high quality geometry; (iii) poor density and difficult or impossible to model. An example of type (ii) is observed for the intra-chain disulphide bridge in chain C(3) between Sγ6–Sγ11 which has two clear conformations with relative refined occupancies of 0.8 and 0.2, respectively. In contrast the corresponding S–S bridge in chain A(1) shows one clearly defined conformation. A molecular dynamics study has provided a rational explanation of this difference between chains A and C. More generally, differences in the electron density features between corresponding residues in chains A and C and chains B and D is a common observation in the Insugen (I) structure and these effects are discussed in detail. The crystal structure, also at 0.92 Å and 100 K, of a second commercially available form of human recombinant insulin, Intergen (II), deposited in the Protein Data Bank as 3W7Y which remains otherwise unpublished is compared here with the Insugen (I) structure. In the Intergen (II) structure there is no solvated propanol or acetate molecule. The electron density of Intergen (II), however, does also exhibit the three types of amino acid representations as in Insugen (I). These effects do not necessarily correspond between chains A and C or chains B and D in Intergen (II), or between corresponding residues in Insugen (I). The results of this comparison are reported.Graphical abstract

Audit of the use of psoralen photochemotherapy (PUVA) and narrowband UVB phototherapy in the treatment of psoriasis

BACKGROUND

Psoralen photochemotherapy (PUVA), the combined use of psoralen and long wave ultraviolet (UVA) irradiation, was introduced around 1974 and its beneficial effects were rapidly confirmed worldwide. In an attempt to minimize its recognized long-term photocarcinogenic risk after some 150-200 exposures while also maintaining efficacy, however, the narrowband (311-312 nm) ultraviolet B (UVB) lamp (TL-01) was introduced in 1984, and has moved towards replacing PUVA except for severe or resistant disease.

AIMS

To discover whether our use of these therapies complied with established British Photodermatology Group guidelines for PUVA and guidelines formulated within our unit for narrowband UVB.

METHODS

The study was retrospective over 6 months from November 2001 to April 2002, all relevant information being obtained from the patients' hospital notes.

RESULTS

Thirty-one patients received PUVA (18 oral, 11 bath and two uncertain because of missing notes) and 20 narrowband UVB during this period.

CONCLUSIONS

Our PUVA and narrowband UVB phototherapy guidelines were shown to have been followed relatively closely with the following exceptions: one PUVA patient received a high cumulative exposure by mutual agreement because there was no other suitable therapy; a failure to measure minimal phototoxic doses (MPDs) in some PUVA patients; and slightly prolonged referral delays, but generally by patient choice.

Structural basis for sugar recognition, including the Tn carcinoma antigen, by the lectin SNA-II from Sambucus nigra

Bark of elderberry (Sambucus nigra) contains a galactose (Gal)/N-acetylgalactosamine (GalNAc)-specific lectin (SNA-II) corresponding to slightly truncated B-chains of a genuine Type-II ribosome-inactivating protein (Type-II RIPs, SNA-V), found in the same species. The three-dimensional X-ray structure of SNA-II has been determined in two distinct crystal forms, hexagonal and tetragonal, at 1.90 A and 1.35 A, respectively. In both crystal forms, the SNA-II molecule folds into two linked beta-trefoil domains, with an overall conformation similar to that of the B-chains of ricin and other Type-II RIPs. Glycosylation is observed at four sites along the polypeptide chain, accounting for 14 saccharide units. The high-resolution structures of SNA-II in complex with Gal and five Gal-related saccharides (GalNAc, lactose, alpha1-methylgalactose, fucose, and the carcinoma-specific Tn antigen) were determined at 1.55 A resolution or better. Binding is observed in two saccharide-binding sites for most of the sugars: a conserved aspartate residue interacts simultaneously with the O3 and O4 atoms of saccharides. In one of the binding sites, additional interactions with the protein involve the O6 atom. Analytical gel filtration, small angle X-ray scattering studies and crystal packing analysis indicate that, although some oligomeric species are present, the monomeric species predominate in solution.

A comparative study of the single crystal X-ray determination and molecular modelling of the binding of oligomycin to ATP synthase

Recently published X-ray structures of three common forms, A, B and C, of oligomycin, including absolute configurations, are investigated to examine their binding to ATP Synthase. The X-ray studies reveal regions with differences in three-dimensional structure and hydrogen bonding propensity between the oligomycins, which may be associated with their potential to bind to sites on ATP Synthase. Computational docking studies carried out using MOE with the X-ray structures and an homology model of the F(O) domain of ATP Synthase from Escherichia coli, are used to derive an induced fit pocket. Docking of all oligomycins to this pocket indicate that the B and C forms bind more tightly than the A form. Consideration of the single crystal X-ray data alone indicate the B form may be the best inhibitor and that O(24) is the most important ligating group for binding, this is supported by the docking data. The latter reveals Asn214 and other key proton translocating residues to be the main residues contacted by the inhibitor. These data allow the binding modes of different forms of oligomycin to be deduced from X-ray single crystal data supported by molecular modelling and computational docking studies.

Persistent severe amiodarone-induced photosensitivity

Amiodarone, a benzofuran derivative, has been used therapeutically as an antiarrhythmic and coronary vasodilator in Europe since 1964. One of its commoner side effects is cutaneous photosensitivity; more rarely, after ingestion of the drug for around 12 months, a slate-grey or violaceous discoloration of sun-exposed sites may gradually develop. Both of these side effects usually resolve within 2 years of discontinuation of the drug. We now present a woman who developed both photosensitivity and a slate-grey discoloration whilst taking amiodarone; on discontinuation of the drug, the dyspigmentation gradually resolved, but the photosensitivity has persisted and the patient remains symptomatic more than 17 years later.

Exacerbation of presumed chronic actinic dermatitis by cockpit visible light in an airline pilot with atopic eczema

Chronic actinic dermatitis (CAD) is a persistent ultraviolet radiation- or visible light-induced eczema of predominantly the exposed areas of usually elderly people. We now present the case of a young pilot with atopic eczema who developed CAD, regularly exacerbated by exposure to visible light through his aircraft cockpit window.

Antagonist binding in the rat muscarinic receptor A study by docking and X-ray crystallography

A series of agonists to the rat muscarinic receptor have been docked computationally to the active site of a homology model of rat M1 muscarinic receptor. The agonists were modelled on the X-ray crystal structure of atropine, which is reported here and the docking studies are shown to reproduce correctly the order of experimental binding affinities for the agonists as well as indicate where there appear to be inconsistencies in the experimental data. The crystal and molecular structure of atropine (tropine tropate; alpha-[hydroxymethyl]benzeneacetic acid 8-methyl[3.2.1]oct-3-yl ester C17H23NO3) has been determined by X-ray crystallography using an automated Patterson search method, and refined by full-matrix least-squares to a final R of 0.0452 for 2701 independent observed reflections and 192 parameters using Mo Kalpha radiation, lambda=0.71073A at 150K. The compound crystallises in space group Fdd2 with Z=16 molecules per unit cell.

A simple method to assess severity of polymorphic light eruption

BACKGROUND

The severity of polymorphic light eruption (PLE) is highly variable. The results of studies of the prevalence, pathogenesis, provocation and treatment of PLE may be highly dependent on the severity of disease in the patients studied.

OBJECTIVES

To produce a simple, valid and reproducible method to assess the severity of PLE.

PATIENTS AND METHODS

Eighty patients were asked about the PLE they had experienced during the preceding 12 months, using a standardized interview comprising 16 questions. The answer to each question received a score. A PLE Severity Index (PLESI) was formulated, consisting of 10 questions, with a possible total score of 2-100. The internal consistency of the PLESI (the extent to which the responses to different questions correlated with each other) was assessed by reliability analysis, using Cronbach's method. Twenty patients were re-interviewed 7-27 days later to assess the repeatability of the PLESI. The ease of provocation of PLE by exposure at 24-h intervals to solar-simulated radiation was assessed on a five-point scale in nine of the 80 subjects (the EOPSSR score).

RESULTS

The value of Cronbach's alpha for the PLESI was 0.77. The distribution of the PLESI was consistent with a normal distribution, with a mean value of 52.7 and standard deviation of 19.4. It had a coefficient of repeatability of 20.1. The PLESI was positively correlated with EOPSSR (rs =0.69, P = 0.039) and the number of years since onset of PLE (rs = 0.25, P = 0.03). There was no association between the PLESI and the duration of persistence of the eruption after ceasing sun exposure (rs = 0.12, P = 0.30), the development of tolerance as summer progressed (rs = -0.14, P = 0.39), gender (P = 0.50) or skin type (P = 0.87).

CONCLUSIONS

This study has (i) validated the concept that a single score can reflect disease severity in PLE by showing that the principal characteristics of the condition, including, for example, the extent of anatomical distribution and the ease of provocation of the eruption, correlate with each other; (ii) formulated the PLESI, which is a simple, valid and reproducible way of assessing disease severity; we suggest it could be used worldwide to determine the severity of PLE among patients enrolled in future PLE research; (iii) shown that the ease with which the eruption is provoked by solar-simulated radiation correlates with the severity of the condition; and (iv) shown that the duration of persistence of the eruption after sun exposure does not correlate with the severity of the condition.

A new gene encoding the ribosome-inactivating protein from mistletoe extracts

Extracts from mistletoe (Viscum album L.) contain three main toxic proteins--the lectins MLI (also known as viscumin), MLII and MLIII. A catalytic subunit of the mistletoe plant toxic lectin MLIII has been cloned and expressed in Escherichia coli cells. The structure and immunochemical properties of recombinant MLIII A-subunit were investigated using a panel of monoclonal antibodies against ML-toxins. Ribosome-inactivating activity of the recombinant MLIII A-subunit was determined in a cell-free system exhibiting inhibition of endogenous protein synthesis. The comparative analysis of nucleotide and deduced amino acid sequences of the cloned MLIII A and the native MLI A-subunits was performed, revealing the main differences in the primary structure of these proteins. Antigenicity analysis of the MLIII A-subunit has revealed a new epitope D179-E184 that is not present in viscumin. The role of toxic lectins with respect to the immunological properties of mistletoe extracts is discussed.

A comparison of six and 12 PUVA treatments in the prophylaxis of polymorphic light eruption

Polymorphic light eruption (PLE) is a common condition for which the most effective treatment is prophylactic phototherapy. This is traditionally given in courses of approximately 12-15 exposures. We compared the effect of six and 12 treatments of psoralen-UVA (PUVA) therapy, in the prophylaxis of PLE, in a side-to-side within-patient comparison pilot study. In six out of eight patients, six treatments provided as much protection as 12 treatments. Five of these six patients had reported relatively mild disease in the previous year, in comparison to the other two patients. In view of the inconvenience and increased incidence of adverse effects associated with long treatment courses, we recommend the use of short courses, particularly in patients who are relatively mildly affected.

Erythrodermic chronic actinic dermatitis responding only to topical tacrolimus

Chronic actinic dermatitis (CAD) is a disorder characterized by an often severe persistent eczematous eruption induced by exposure to ultraviolet radiation. Treatment involves photoprotective measures and topical corticosteroid therapy and in more severe cases, systemic immunosuppression. Occasionally, however, the condition can prove very resistant to all therapy and be severely disabling. We report a patient with CAD who resisted standard topical and systemic treatments, but responded to topical tacrolimus ointment 0.1% (Protopic).

X-ray crystallographic studies of protein–ligand interactions

X-ray crystallography enables details of covalent and non-covalent interactions to be analysed quantitatively in three dimensions, thus providing the basis for the understanding of binding of ligands to proteins as well as modes of action such as cell-surface binding. This article is concerned with current methods employed for the X-ray analysis of protein structures complexed with ligands. It deals mainly with ‘what can be done’ in current research, rather than providing details of ‘how to do it’. In recent years significant advances have been made in a variety of techniques: growing protein crystals from very small samples by scanning a wide range of conditions; X-ray intensity data collection and measurement through the use of charge-coupled devices and high-intensity, versatile synchrotron sources; cryo-crystallography which both stabilizes the crystals and provides improved data; methods for analysing and interpreting the structures, dependent, at least in part, on both structural and sequence databases; and improvements in hardware and software. To illustrate the type of results achievable two examples involving protein–sugar interactions are discussed: (i) SNAII (the lectin Sambucus nigra agglutinin-II from elder) N-terminal sugar-binding site where terminal sugar units in a glycosylation chain from a symmetry-related molecule bind and (ii) MLI (mistletoe lectin I) C-terminal sugar-binding site with lactose.

Crystal structure at 3 A of mistletoe lectin I, a dimeric type-II ribosome-inactivating protein, complexed with galactose

The X-ray structure of mistletoe lectin I (MLI), a type-II ribosome-inactivating protein (RIP), cocrystallized with galactose is described. The model was refined at 3.0 A resolution to an R-factor of 19.9% using 21 899 reflections, with Rfree 24.0%. MLI forms a homodimer (A-B)2 in the crystal, as it does in solution at high concentration. The dimer is formed through contacts between the N-terminal domains of two B-chains involving weak polar and non-polar interactions. Consequently, the overall arrangement of sugar-binding sites in MLI differs from those in monomeric type-II RIPs: two N-terminal sugar-binding sites are 15 A apart on one side of the dimer, and two C-terminal sugar-binding sites are 87 A apart on the other side. Galactose binding is achieved by common hydrogen bonds for the two binding sites via hydroxy groups 3-OH and 4-OH and hydrophobic contact by an aromatic ring. In addition, at the N-terminal site 2-OH forms hydrogen bonds with Asp27 and Lys41, and at the C-terminal site 3-OH and 6-OH undergo water-mediated interactions and C5 has a hydrophobic contact. MLI is a galactose-specific lectin and shows little affinity for N-acetylgalactosamine. The reason for this is discussed. Structural differences among the RIPs investigated in this study (their quaternary structures, location of sugar-binding sites, and fine sugar specificities of their B-chains, which could have diverged through evolution from a two-domain protein) may affect the binding sites, and consequently the cellular transport processes and biological responses of these toxins.

Two new cyclosporin folds observed in the structures of the immunosuppressant cyclosporin G and the formyl peptide receptor antagonist cyclosporin H at ultra-high resolution

Cyclosporins are cyclic undecapeptides of fungal origin the best known of which, CsA, is a lead clinical immunosuppressant; CsG is a potential clinical immunosuppressant differing from CsA in residue 2 (L-alpha-amino-butyric acid in CsA, L-norvaline in CsG); and CsH is an inverse formyl peptide receptor agonist, differing from CsA in the chiral inversion of MeVal-11 from L to D. Crystal structure determinations of CsG and CsH were undertaken to identify structural and surface features important for biological activity and the future design of new cyclosporin derivatives. Ultra-high resolution X-ray structures (0.80 to 0.87 A resolution) determined for two crystal forms of both CsH and CsG in the presence and absence of Mg2+ are described. A major outcome of this study is the observation that the local change in chirality between CsA and CsH is associated with a major structural transformation from open beta-sheet in CsA to a highly convoluted conformation in CsH. CsG also possesses a completely novel cloverleaf motif with no H-bonded secondary structure features in spite of the minimal chemical difference with CsA. Unlike CsA, the structures of both CsH and CsG are heavily solvated. This study therefore shows that the chemical differences between the three cyclosporins, CsA, CsG and CsH can invoke unpredictably major differences in their 3D structures. The 9-11 cis-peptide bond in CsA moves to 11-1 in CsG, influencing the overall molecular conformation, while the peptide bonds in the highly convoluted loop conformation of CsH are all trans.

Vancomycin-induced linear IgA disease with autoantibodies to BP180 and LAD285

Linear IgA disease (LAD) is an acquired autoimmune subepidermal bullous disease characterized by the linear deposition of IgA at the basement membrane zone. A minority of cases are induced by drugs, of which the most frequently implicated is vancomycin. The target antigens in idiopathic LAD are heterogeneous, but have not previously been reported in vancomycin-induced LAD. We report three cases, and in two of these we investigated the target antigens. In both we identified IgA antibodies to LAD285 and IgA and IgG antibodies (dual response) to BP180.

Early-onset hidradenitis suppurativa

A 9-year-old girl developed hidradenitis suppurativa 3 months after the first signs of adrenarche. Such a close temporal relationship is consistent with the hypothesis that the disease is androgen dependent. Less than 2% of patients have onset of the disease before the age of 11 years. The exceptionally early age of onset in our patient may be partly explained by the fact that she had an early puberty.

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.

Homozygous variegate porphyria: a compound heterozygote with novel mutations in the protoporphyrinogen oxidase gene

Homozygous variegate porphyria results from mutations in both alleles of the protoporphyrinogen oxidase (PPOX) gene. Our patient, a 36-year-old woman, has severe cutaneous manifestations. Her clinical and biochemical features are similar to the few other reported cases, including onset before 18 months of age, photosensitivity, absence of acute porphyric attacks, and elevated erythrocyte protoporphyrin. Mutation analysis of the PPOX gene revealed an in-frame 12 bp insert (c. 657-658 ins AAGGCCAGCGCC) encoding lysine-alanine-serine-alanine (KASA), and a G to A transition at the splice donor site of exon 11 (IVS 11-1 G-->A). Neither of these mutations has been reported previously. Our patient's mother has the splice site mutation and has had acute porphyric episodes. A maternal first cousin has the same mutation but no clinical manifestations. The medical and family history of our patient's father is uncertain.

The management of cutaneous leishmaniasis from Belize

We report 20 patients who contracted cutaneous leishmaniasis in Central and South America, 18 of them in Belize. The diagnosis was confirmed by the polymerase chain reaction (PCR) in 79% of those tested; the corresponding figure for histology was 62%, touch smear 46%, and culture 11%. Results of PCR can be falsely positive, so treatment should not be based on PCR alone. Of the 20 cases 18 were healed 6 weeks after intravenous sodium stibogluconate 20 mg/kg per day for 20 days. We present a management protocol.

(24R)-24,25-Dihydroxycycloartan-3-one

In the title compound, C(30)H(50)O(3), the three six-membered rings adopt chair, twist and twist-boat conformations. The five-membered ring is in a slightly distorted envelope conformation. The substituent on the five-membered ring is in an extended conformation, with its two hydroxyl O atoms forming an intramolecular hydrogen bond. One of these O atoms also forms an intermolecular hydrogen bond with the oxygen of the carbonyl group in a neighbouring molecule.

A double mesogen based on linkedp-terphenyl units

The structure of bis(4,4"-decyloxy-p-terphenyl-2'-ylmethyl) carbonate, C(79)H(110)O(7), (I), has been determined at 123 K. It is a new type of twin mesogen. No two adjacent aromatic rings are coplanar and the four decyloxy side chains are maximally extended. Molecules of the compound are packed along the crystallographic a axis. The molecular arrangement is a precursor of a smectic A phase.

Step-scan FTIR time-resolved spectroscopy study of excited-state dipole orientation in soluble metallopolymers

Step-scan FTIR time-resolved spectroscopy (S2FTIR TRS) in acetonitrile-d3 has been used to probe the acceptor ligand in metal-to-ligand charge transfer (MLCT) excited states of amide-substituted polypyridyl complexes of RuII and in analogues appended to polystyrene. On the basis of ground-to-excited state shifts in v(C = O) of -31 cm-1 for the amide group in [RuII(bpy)2(bpyCONHEt')]2+ (bpyCONHEt' = 4'-methyl-2,2'-bipyridine-4-carboxamide-Et'; Et' = -CH2CH2BzCH2CH3) (1) and in the derivatized polystyrene abbreviated [PS-[CH2-CH2NHCObpy-RuII(bpy)2]20]40+ (3), the excited-state dipole is directed toward the amide-containing pyridyl group in the polymer side chain. Smaller shifts in v(C = O) of -17 cm-1 in [RuII(4,4'-(CONEt2)2bpy)2-(bpyCONHEt')]2+ (2) and in the derivatized polystyrene abbreviated [PS-[CH2CH2NHCObpy-RuII(4,4'-(CONEt2)2bpy)2]20]40+ (4) indicate that the excited-state dipole is directed toward one of the diamide bpy ligands. The nearly identical results for 1 and 3 and for 2 and 4 show that the molecular and electronic structures of the monomer excited states are largely retained in the polymer samples. These conclusions about dipole orientation in the polymers are potentially of importance in understanding intrastrand energy transfer dynamics. The excited-state dipole in 3 is oriented in the direction of the covalent link to the polymer backbone, and toward nearest neighbors. In 4, it is oriented away from the backbone.

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.

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.

The hospital library is crucial to quality healthcare

In a 1988 report, an advisory committee of the Medical Library Association (MLA) wrote that "no one would argue against information as the foundation for efficient cost-effective business or against access to knowledge as a prerequisite for developing new knowledge." Yet the increasing number of threats to the hospital library--largely from within the industry--suggest that many hospitals do not value information in the same way their counterparts in other businesses do. In the first of two articles in this issue on hospital library and information services, the executive director of the MLA uses the MLA's experience and a variety of research findings to restate the case for the hospital library's vital role in quality care.

Mistletoe lectin I forms a double trefoil structure

The quaternary structure of mistletoe lectin I (MLI), a type II ribosome inactivating protein, has been determined by X-ray crystallography. A definitive molecular replacement solution was determined for MLI using the co-ordinates of the homologue ricin as a search model. MLI exists as an [AB]2 dimer with internal crystallographic two-fold symmetry. Domain I of the B chains is non-covalently associated through interactions involving three looped chains (alpha, beta, gamma) in each molecule of the dimer, forming a double trefoil structure. The ricin molecule which shares 52% sequence homology with MLI has a disulphide bridge between Cys20 and Cys39 in the alpha loop. An evolutionary mutation has replaced Cys39 with serine in MLI. This mutation appears to allow the alpha loop the flexibility required to take up its place at the dimer interface, and also suggests a rationale for why ricin does not form dimers. Measurement of retention times using FPLC gel filtration confirms that dimerisation also occurs in solution between MLI B chains with an association constant Ka = 10(6) M.

Preliminary crystallographic characterization of ricin agglutinin

The quaternary structure of ricin agglutinin (RCA) has been determined by x-ray crystallography. The refined structure of ricin proved to be a successful search model using the molecular replacement method of phase determination. RCA forms an elongated molecule of dimensions 120 A x 60 A x 40 A with two A chains at the center and a B chain at each end. The A chains are covalently associated via a disulfide bridge between Cys 156 of both chains. Additional contacts at residues 114-5 stabilize the dimer interface. The covalent association of RCAA chains was confirmed by gel filtration under reducing and nonreducing conditions.

The role of structural domains in RIP II toxin model membrane binding

The interaction of plant toxin ricin and MLI binding subunits to liposomes containing monosialoganglioside (GM1), bearing a terminal galactose residue, has been examined as a possible receptor model. For the first time we demonstrate that ricin B-chain but not ricin provokes liposome aggregation at 10 M% GM1 concentration, whereas in the presence of either ricin A-chain or galactose the aggregation is inhibited. The B-subunit of plant toxin MLI from Viscum album has similar lectin specificity and activity but cannot aggregate GM1 liposomes. The ability of the B-chain to aggregate liposomes adds a new crucial step in the toxin transmembrane penetration mechanism. We demonstrate here possible ricin B-chain interactions with membranes proceeding via two sites, namely (a) a galactose-binding domain and (b) a hydrophobic interchain domain. In close contact with two phospholipid bilayers, ricin B-chain may determine the geometry of the fusion site. These events can provoke A-chain translocation which follows membrane fusion.

Structure of the crystalline complex of deoxycytidylyl-3',5'-guanosine (3',5'-dCpdG) cocrystallized with ribonuclease at 1.9 Å resolution

The X-ray structure of bovine ribonuclease A cocrystallized with the dinucleotide deoxycytidylyl-3',5'-guanosine has been determined at 1.9 A resolution and refined by restrained least squares to R = 0.218 for 7807 reflections. The structure established that the recently observed retrobound mode of attachment of substrate analogues cytidylyl-2',5'-guanosine and deoxycytidylyl-3',5'-guanosine found in soaked RNase A crystals is also present in the cocrystallized complex. Retrobinding is thus unlikely to be the result of restrictions imposed by the crystalline environment as the ligands soak into the lattice but rather a phenomenon specific to small nucleotides containing guanine.

Activity of the Stable Intermediate form of Heat Treated Ricin B-Chain

Abstract:

Intrinsic fluorescence and NMR-spectroscopy demonstrate that heat treatment of the ricin carbohydrate binding subunit (RTB) leads to partial unfolding to an intermediate stable state with enhanced amino acid side chain mobility and a redistribution of surface charges. RTB continues to facilitate transmembrane translocation of the enzymatically active ricin subunit (RTA) although its lectin activity and ability to interact with RTA are dramaticaJiy reduced following this thermal modification. The proposal that RTB potentiates membrane translocation of the A-chain in this intermediate folded state is discussed.

Diet of the red fox (Vulpes vulpes) in south-western Queensland

Examination of the stomach contents of 74 foxes from a south-western Queensland sheep grazing property revealed a diverse range of prey. Mammals formed the bulk of the diet representing 64% of the total weight of food items and occurred in 80% of stomachs. Sheep and kangaroo carrion were the main mammalian prey. Insects and other invertebrates were an important but lesser component of the diet. Dietary trends were heavily influenced by human activity, rainfall, and season. These results differ from those of other studies conducted in southern parts of Australia due to the large proportions of scavenged food items in the diet (63% by weight) and relatively high consumption levels of non-mammalian prey. The lack of a small to medium sized staple prey source in the study area, which were available in southern areas appears to be the reason for the foxes reliance on such a varied prey base.

Fred W. Roper Medical Library Association President 1994-1995

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The master librarian: Lucretia McClure

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