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PubMed2005

Asymmetric total synthesis of complex marine natural products.

Among nature's ecosystems, the marine environment has been an extremely rich source of structurally complex and biologically active molecules. This review aims to cover the recent developments in the synthesis of marine natural products, also reflecting the trend of their increased use to address biological questions. The examples chosen should be viewed as representative of the different structural motifs on the one hand and the strategies and stimuli for their synthesis on the other.

Aquaculture↗
PubMed2003

Molecular and electronic structures of iron complexes containing N,S-coordinated, open-shell o-iminothionebenzosemiquinonate(1-) pi radicals.

The reaction of the dinuclear species (mu-NH,NH)[Fe(III)(L(IP))(L(AP))](2) dissolved in CH(2)Cl(2) with dioxygen affords black microcrystals of diamagnetic (mu-S,S)[Fe(III)(L(IP))(L(ISQ))](2).n-hexane (6) upon the addition of n-hexane, where (L(IP))(2)(-) represents the dianion of 4,6-di-tert-butyl-2-aminothiophenol, (L(AP))(-) is the corresponding monoanion, and (L(ISQ))(-) is the corresponding o-iminothionebenzosemiquinonate(1-) pi radical monoanion; similarly, the dianion ('H(2)N(2)S(2)')(2)(-) is derived from 1,2-ethanediamine-N,N'-bis(2-benzenethiol), and ('N(2)S(2)(*)')(3)(-) is its monoradical trianion. The above reaction in a CH(2)Cl(2)/CH(3)OH (1:1) mixture yields the diamagnetic isomer (mu-NH,NH)[Fe(III)(L(IP))(L(ISQ))](2).5CH(3)OH (7), whereas air oxidation of (mu-S,S)[Fe(II)('H(2)N(2)S(2)')](2) in CH(3)CN yields diamagnetic (mu-S,S)[Fe(III)('N(2)S(2)(*)')](2) (8). Complexes 6 and 8 were shown to undergo addition reactions with phosphines, phosphites, or cyanide affording the following complexes: trans-[Fe(II)(L(ISQ))(2)(P(OPh)(3))] (9; S(t) = 0) and [N(n-Bu)(4)][Fe(II)(L(ISQ))(2)(CN)] (S(t) = 0). Oxidation of 6 in CH(2)Cl(2) with iodine, bromine, and chlorine respectively yields black microcrystals of [Fe(III)(L(ISQ))(2)X] (X = I, Br, or Cl) with S(t) = (1)/(2). The structures of complexes 6-9 have been determined by X-ray crystallography at 100 K. The oxidation level of the ligands and iron ions in all complexes has been unequivocally established, as indicated by crystallography; electron paramagnetic resonance, UV-vis, and Mössbauer spectroscopies; and magnetic-susceptibility measurements. The N,S-coordinated o-iminothionebenzosemiquinonate(1-) pi radicals have been identified in all new complexes. The electronic structures of the new complexes have been determined, and it is shown that no evidence for iron oxidation states >III is found in this chemistry.

Journal Article↗
PubMed2007

Structure of polyelectrolyte complexes by Brownian dynamics simulation: effects of the bond length asymmetry of the polyelectrolytes.

Brownian dynamics simulations were performed to study the structure of polyelectrolyte complexes formed by two flexible, oppositely charged polyelectrolyte chains. The distribution of monomers in the complex as well as the radius of gyration and structure factor of complexes and individual polyelectrolytes are reported. These structural properties were calculated for polyelectrolyte chains with equal number of monomers, keeping constant the bond length of the negative chain and increasing the bond length of the positive chain. This introduces an asymmetry in the length of the chains that modulates the final structure of the complexes. In the symmetric case the distribution of positive and negative monomers in the complex are identical, producing clusters that are locally and globally neutral. Deviations from the symmetric case lead to nonuniform, asymmetric monomer distributions, producing net charge oscillations inside the complex and large changes in the radius of gyration of the complex and individual chains. From the radius of gyration of the polyelectrolyte chains it is shown that the positive chain is much more folded than the negative chain when the chains are asymmetric, which is also confirmed through the scaling behavior of the structure factors.

Journal Article↗
PubMedDate not supplied

[Analysis of defects in the structure of the complex poly(G).poly(C)].

The concentration of free poly(C) in solution in the course of its interaction with poly(G) as well as in the presence of preformed complex poly(G).poly(C) was measured by differential pulse polarography (DPP) at a mercury dropping electrode. Poly(C) binding with poly(G) was shown to hamper its electrochemical interaction with the mercury electrode and registration by DPP. It was concluded that the extremely low DPP signal from poly(C) in the presence of preformed complex was the result of its interaction with the distortions in the secondary structure of complex molecules containing free guanines. For quantitative testing of these defects, measurement of Tb3+ ion fluorescence was applied. It was shown that preliminary denaturation of the poly(G) secondary structure reduced the amount of structural defects in the complex and restored of complete DPP registration of redundant poly(C) added to this complex. These results show that the combination of DPP and Tb3+ fluorescence measurements permits one to detect at the quantitative level the structural defects in the poly(G).poly(C) complex.

Electrochemistry↗
PubMed1999

Crystal structure of a conserved ribosomal protein-RNA complex.

The structure of a highly conserved complex between a 58-nucleotide domain of large subunit ribosomal RNA and the RNA-binding domain of ribosomal protein L11 has been solved at 2.8 angstrom resolution. It reveals a precisely folded RNA structure that is stabilized by extensive tertiary contacts and contains an unusually large core of stacked bases. A bulge loop base from one hairpin of the RNA is intercalated into the distorted major groove of another helix; the protein locks this tertiary interaction into place by binding to the intercalated base from the minor groove side. This direct interaction with a key ribosomal RNA tertiary interaction suggests that part of the role of L11 is to stabilize an unusual RNA fold within the ribosome.

Amino Acid Sequence↗
PubMed1993

Stoichiometry of the human lysosomal carboxypeptidase-beta-galactosidase complex.

The understanding of the lysosomal beta-galactosidase-carboxypeptidase-neuraminidase multienzymatic complex structure and function requires an efficient system for dissociation and association of its isolated protein components under controlled conditions. In this paper such a system was used to determine the stoichiometry of the two main components of this complex--beta-galactosidase and carboxypeptidase. The complex, after affinity purification from human placenta, was dissociated at pH 7.5 and beta-galactosidase and carboxypeptidase were separated and purified to homogeneity by FPLC anion-exchange chromatography. The 680 kD complex of beta-galactosidase and carboxypeptidase was reconstituted in vitro by mixing the isolated enzymes in a 1:2 molar ratio at pH 7.5 and then progressively acidifying the medium towards the intralysosomal pH value of 4.75. Under the same conditions, beta-galactosidase and carboxypeptidase independently existed as 306 kDa tetramer and 98 kDa dimer, respectively. Reconstitution experiments with various ratios of purified beta-galactosidase and carboxypeptidase allowed us to conclude that the whole complex is made of 4 beta-galactosidase and 8 carboxypeptidase monomers. Cross-linking of the native and reconstituted complexes with dimethylsuberimidate or glutaric dialdehyde suggested that the native and the reconstituted complexes have the same supramolecular structure.

Carboxypeptidases↗
PubMed1993

7-S-glutathionyl-tryptamine-4,5-dione: a possible aberrant metabolite of serotonin.

Tryptamine-4,5-dione (Compound 1) is an in vitro oxidation product of 5-hydroxytryptamine (5-HT). Recent evidence has suggested that aberrant oxidations of 5-HT occur in the central nervous system of individuals with Alzheimer's disease (AD). In the event that Compound 1 is formed as a result of oxidation of 5-HT within serotonergic nerve terminals or axons, it would be expected to be rapidly conjugated by intraneuronal glutathione (GSH) to give 7-S-glutathionyl-tryptamine-4,5-dione (Compound 2). When injected into the brains of laboratory mice, Compound 2 was lethal (LD50 = 21 micrograms) and evoked hyperactivity for the first 30 min following drug administration. Particularly during this hyperactive phase Compound 2 caused a statistically significant decrease in whole brain levels of norepinephrine and 5-HT. Levels of dopamine were also decreased while whole brain concentrations of its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, were increased significantly. In the presence of GSH, NADPH and ascorbic acid, Compound 2 redox cycled in reactions that catalyzed the oxidation of these cellular reductants by molecular oxygen and formed H2O2 as a byproduct. Compound 2 also reacted with molar excesses of GSH to form more structurally complex glutathionyl conjugates. Several of these conjugates have been isolated and their structures determined using spectroscopic methods. It is conceivable that one or more of these conjugates might serve as analytical markers in a search for evidence in support of the hypothesis that aberrant oxidations of 5-HT occur in the Alzheimer brain. The redox cycling properties of Compound 2 and its facile reactions with cellular nucleophiles such as GSH may represent mechanisms that contribute to the toxicity of this drug.

Acetylcholine↗
PubMed2001

The dimeric complex of cyclomaltoheptaose with 1,14-tetradecanedioic acid. Comparison with related complexes.

The structure of the complex of cyclomaltoheptaose (beta-cyclodextrin, betaCD) with 1,14-tetradecanedioic acid has been determined and refined to a final R=0.0693 based on 9824 observed reflections. Each diacid molecule threads through two betaCD monomers arranged in dimers thus, forming a [3]pseudorotaxane. The end carboxylic groups of adjacent dimers, far apart and fully hydrated, are associated indirectly through water molecules. The positioning of the carboxylic groups with respect to the betaCD dimer and the H-bonds with water molecules are very similar to these of the corresponding complexes of the diacids with 12 and 13 carbon atoms. The bending in the middle of the aliphatic chain is more prominent, compared to that of the corresponding guests with less carbon atoms, thus the end carboxylic groups stay in the same height of the primary faces of the betaCD dimeric complex. As a consequence of the present structure, more close contacts are observed between calculated H-atoms of the guest and O-atoms of the host inside the cavity. This bending is allowed by the width of the betaCD dimer cavity at the secondary interface region.

Bridged-Ring Compounds↗
PubMed1997

Direct analysis of sugar alcohol borate complexes in plant extracts by matrix-assisted laser desorption/ionization fourier transform mass spectrometry.

Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI/FTMS), operating in the negative ion mode, is used to directly observe sugar alcohol borate complexes in a number of plant fractions. The method involves virtually no sample workup and, in the case of celery phloem sap, requires only 40 nL of sap to observe the borate complex. The isolation and characterization of such soluble borate complexes is important in understanding the distribution of boron in plants. The results show that the complexes are composed of two mannitol or sorbitol ligands (L) complexed to a single borate center (B). In some cases, the boron is complexed to non-alditol monosaccharides. Sustained off-resonance collision irradiation dissociation of the BL2- complex, where L is a mannitol, gives fragments that confirm the proposed structure. Complexes of larger oligosaccharides have also been successfully observed using MALDI/FTMS. Semiempirical molecular orbital calculations (AM1) of the mannitol BL2- complex show that the most favorable configuration is with carbons 3 and 4 of both mannitol residues complexed to the borate. This allows maximum interaction of the remaining hydroxyls with the borate center.

Borates↗
PubMed1992

Partial Purification and Characterization of Complex I, NADH:Ubiquinone Reductase, from the Inner Membrane of Beetroot Mitochondria.

A NADH dehydrogenase was isolated from an inner membrane-enriched fraction of beetroot mitochondria (Beta vulgaris L.) by solubilization with sodium deoxycholate and purified using gel filtration and affinity chromatography. The NADH dehydrogenase preparation contained a minor ATPase contamination. Beetroot mitochondria were chosen as the isolation material for purifying the enzymes responsible for oxidizing matrix NADH due to the absence of the externally facing NADH dehydrogenase in the variety we have used. The purified NADH dehydrogenase complex catalyzed the reduction of various electron acceptors with NADH as the electron donor, was not sensitive to rotenone inhibition, and had a slow NADPH-ubiquinone 5 reductase activity. The isolated complex contained 14 major polypeptides. It was concluded that the dehydrogenase represented a form of the plant mitochondrial complex I and not the internally facing rotenone-insensitive NADH dehydrogenase found in plant mitochondria because of its complex structure, its cross-reactivity with antisera raised against bovine heart mitochondrial complex I, and the similarity of its kinetics and inhibitor responses to rotenone-sensitive NADH oxidation by beetroot submitochondrial particles.

Journal Article↗
PubMedDate not supplied

ClearView: An interactive context preserving hotspot visualization technique.

Volume rendered imagery often includes a barrage of 3D information like shape, appearance and topology of complex structures, and it thus quickly overwhelms the user. In particular, when focusing on a specific region a user cannot observe the relationship between various structures unless he has a mental picture of the entire data. In this paper we present ClearView, a GPU-based, interactive framework for texture-based volume ray-casting that allows users which do not have the visualization skills for this mental exercise to quickly obtain a picture of the data in a very intuitive and user-friendly way. ClearView is designed to enable the user to focus on particular areas in the data while preserving context information without visual clutter. ClearView does not require additional feature volumes as it derives any features in the data from image information only. A simple point-and-click interface enables the user to interactively highlight structures in the data. ClearView provides an easy to use interface to complex volumetric data as it only uses transparency in combination with a few specific shaders to convey focus and context information.

Algorithms↗
PubMed1991

Simple mucin-type carbohydrates in oral stratified squamous and salivary gland epithelia.

Simple mucin-type carbohydrate antigens, T, Tn, and sialosyl-Tn, have been found to be good markers of malignant transformation in several epithelial tissues as a result of incomplete synthesis with precursor accumulation. The T, Tn, and sialosyl-Tn antigens represent the initial, most immature glycosylation of serine and threonine amino acids of proteins. In normal adult cells these structures are generally masked by addition of further saccharides to form more complex structures. We analyzed simple mucin-type carbohydrates in human labial stratified squamous and minor salivary gland epithelia in order to define the glycosylation pattern in normal cells in relation to epithelial differentiation and maturation. A panel of monoclonal antibodies with well-characterized specificity for T, Tn, sialosyl-Tn and the histo-blood group H and A variants hereof were used in immunohistology of sections from 30 individuals with known ABO, Lewis, and secretor status. In stratified epithelium the sialylated T structure was confined to cell membranes of immature basal cells, whereas the H and A variants were observed on cell membranes of more mature parabasal and spinous cell layers. Furthermore, superficial spinous cells produced a fine granular cytoplasmic staining for Tn and sialosyl-Tn antigens. In minor salivary glands mucous cells expressed Tn and sialosyl-Tn as well as the H and A variants in the area of the nucleus, whereas T and the H variant were found in duct cells and unsubstituted T antigen in myoepithelial cells. These results indicate that incomplete synthesis, i.e., deletion of sialyltransferases and/or histo-blood group ABH transferases, may result in accumulation of T, Tn, and sialosyl-Tn antigens in oral epithelia, thus offering a baseline for further studies of changes in premalignant and malignant oral epithelia.

Antibodies, Monoclonal↗
PubMed2000

Seeing the herpesvirus capsid at 8.5 A.

Human herpesviruses are large and structurally complex viruses that cause a variety of diseases. The three-dimensional structure of the herpesvirus capsid has been determined at 8.5 angstrom resolution by electron cryomicroscopy. More than 30 putative alpha helices were identified in the four proteins that make up the 0.2 billion-dalton shell. Some of these helices are located at domains that undergo conformational changes during capsid assembly and DNA packaging. The unique spatial arrangement of the heterotrimer at the local threefold positions accounts for the asymmetric interactions with adjacent capsid components and the unusual co-dependent folding of its subunits.

Capsid↗
PubMed1996

Translation initiation in GB viruses A and C: evidence for internal ribosome entry and implications for genome organization.

GB viruses A and C (GBV-A and GBV-C) are two recently described RNA viruses which appear to be members of the Flaviviridae. Although both viruses appear to contain long 5' nontranslated regions, the sites of polyprotein initiation and the presence of core-like proteins remain to be determined. Translation studies were undertaken to determine the mechanism and sites of polyprotein initiation in GBV-A and GBV-C. Rabbit reticulocyte lysates programmed with monocistronic RNAs containing 5' ends of GBV-A or GBV-C fused in-frame with the chloramphenicol acetyltransferase (CAT) open reading frame generated GBV-CAT fusion proteins in vitro. Site-specific mutagenesis and N-terminal sequencing located the sites of translation initiation immediately upstream of the putative signal sequence for the GBV E1 envelope glycoproteins. Efficient translation of the monocistronic GBV-CAT RNAs required the inclusion of GBV coding sequences. This, coupled with the presence of at least 523 nucleotides of 5' nontranslated RNA containing multiple AUG codons, suggests that translation initiation of these RNAs did not utilize a ribosome scanning mechanism. Translation of bicistronic RNAs containing 5' nontranslated sequences within the intercistronic space was consistent with the presence of a weakly active internal ribosome entry site in both GBV-A and GBV-C. Secondary structure predictions indicate that the 5' ends of these viruses assume similar complex structures distinct from those identified in the internal ribosome entry site-containing picornaviruses, pestiviruses, and hepatitis C viruses. The data indicate that GBV-A and GBV-C are unique members of the Flaviviridae that do not contain core-like proteins at the N termini of their putative polyproteins.

Amino Acid Sequence↗
PubMed2003

Mapping of movement in the isometrically contracting human soleus muscle reveals details of its structural and functional complexity.

It is becoming increasingly apparent that precise knowledge of the anatomic features of muscle, aponeurosis, and tendons is necessary for understanding how a muscle-tendon complex generates force and accomplishes length changes. This report presents both anatomic and functional data from the human soleus muscle acquired by using magnetic resonance imaging. The results show a strong relationship between the complex three-dimensional structure of the muscle-tendon system and the intramuscular distribution of tissue velocities during in vivo isometric contractions. The proximal region of the muscle is unipennate, whereas the midregion has a radially bipennate hemicylindrical structure, and the distal region is quadripennate. Tissue velocity mapping shows that the highest velocity regions overlay the aponeuroses connected to the Achilles tendon. These are located on the anterior and posterior surfaces of the muscle. The lowest velocities overlay the aponeuroses connected to the origin of the muscle and are generally located intramuscularly.

Adult↗
PubMedDate not supplied

The role of professional networks in radiology services.

Recent developments in public health policy have high-lighted the central role of the clinical work force in the success of policy implementation, and thus the need for effective human resource policies. Given the high level of professionalism in health services, a number of special issues arise, including the organizational structures that best support professional work. Experiences from global industries that rely on a highly expert work force show that hierarchical control structures need to be supplemented by a variety of networks. Networks are complex structures that are very different from normal hierarchies, and they need to be effectively understood. While they usually develop spontaneously, they are often not optimally structured, adequately supported, or effectively exploited by health service organizations. It is important to understand the nature of networks and how they can be promoted in order to ensure that clinicians are appropriately supported in providing and enhancing services.

Delivery of Health Care↗
PubMedDate not supplied

[Epigenetic and synergistic types of inheritance of the reproductive characters in angiosperms].

The author considers three types of hereditary memory (structural, cell and signal), that are realized on different levels of biological organization. These three types of hereditary memory correspond to three types of reproduction: self-replication, cell division and reproduction s. str. Reproductive characters are exemplified with three essential characters in angiosperm plants: dimorphism in population by flower sex; mono-, di- and trystyly of flowers; uni- and biparental mode of seed reproduction. All these characters are considered as "supercharacters" that are controlled by gene ensembles. The correspondence between three types of reproduction and three types of hereditary memory are discussed. The authors reviews also the role of polyploidy (auto- and endoploidy) in the inheritance of reproductive condition. From the information theory point the increase in cell ploidy causes the growth of uncertainty in expression of genes and gene ensembles thus creating new type of variability--epigenetic variation. The change of reproductive strategy in plants is regulated by state of gene and gene ensembles and does not demand structural changes in genome. The reproductive characters of plants in spite its complex structure are inherited in number of generations as a discrete Mendel characters by mono-, di-, ot trihybrid schemas.

Biological Evolution↗
PubMed1990

Isolation and characterization of calcium binding glycoproteins of cardiac sarcolemmal vesicles.

Two major Ca2(+)-binding glycoproteins Mr 120,000 and 100,000 were isolated from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid -solubilized bovine heart sarcolemma membrane. Peroxidase-conjugated concanavalin A and wheat germ agglutinin lectins bind strongly to the isolated 120- and 100-kDa glycoproteins. Treatment with endoglycosidase F resulted in conversion of the 120-kDa glycoprotein to a form migrating at about 97 kDa. Treatment of the 100-kDa band with endoglycosidase F produced form of about 80 kDa. Endoglycosidase H digestion removes only 5% of the mass of both glycoproteins. the carbohydrate structure of both glycoproteins, is therefore, predicted to be at least 75% complex structure and 25% high mannose or hybrid structure. The 120- and 100-kDa glycoproteins are the major Ca2(+)-binding proteins in the sarcolemma membranes. Intact and endoglycosidase-treated glycoproteins bind 45Ca2+ as analyzed by a 45Ca2+ overlay technique. Using polyclonal antibodies, the 120- and 100-kDa glycoproteins were identified in muscle plasma membranes (ventricles, atria, and uterus smooth muscle). They were, however, not present in non-muscle tissues such as pancreas, liver, and kidney. The 120- and 100-kDa glycoproteins appear to be homologous molecules as judged by their similar V8 protease peptide maps, cross-reactivity with polyclonal antibody, and other physicochemical properties.

Acetylglucosaminidase↗