Imaging membrane protein helical wheels

Resonance patterns have been observed in 2D solid-state NMR spectra of the transmembrane segment of M2 protein from Influenza A virus in oriented samples reflecting the helical wheel of this alpha-helix. The center of this pattern uniquely defines the helical tilt with respect to the bilayer normal without a need for resonance assignments. The distribution of resonances from amino acid specific labels around the "PISA wheel" defines the rotational orientation of the helix and yields preliminary site-specific assignments. With assignments high-resolution structural detail, such as differences in tilt and rotational orientation along the helical axis leading to an assessment of helical coiling, can be obtained.

Inhibition of viral adhesion and infection by sialic-acid-conjugated dendritic polymers

Multiple sialic acid (SA) residues conjugated to a linear polyacrylamide backbone are more effective than monomeric SA at inhibiting influenza-induced agglutination of red blood cells. However, "polymeric inhibitors" based on polyacrylamide backbones are cytotoxic. Dendritic polymers offer a nontoxic alternative to polyacrylamide and may provide a variety of potential synthetic inhibitors of influenza virus adhesion due to the wide range of available polymer structures. We evaluated several dendritic polymeric inhibitors, including spheroidal, linear, linear-dendron copolymers, comb-branched, and dendrigraft polymers, for the ability to inhibit virus hemagglutination (HA) and to block infection of mammalian cells in vitro. Four viruses were tested: influenza A H2N2 (selectively propagated two ways), X-31 influenza A H3N2, and sendai. The most potent of the linear and spheroidal inhibitors were 32-256-fold more effective than monomeric SA at inhibiting HA by the H2N2 influenza virus. Linear-dendron copolymers were 1025-8200-fold more effective against H2N2 influenza, X-31 influenza, and sendai viruses. The most effective were the comb-branched and dendrigraft inhibitors, which showed up to 50000-fold increased activity against these viruses. We were able to demonstrate significant (p < 0.001) dose-dependent reduction of influenza infection in mammalian cells by polymeric inhibitors, the first such demonstration for multivalent SA inhibitors. Effective dendrimer polymers were not cytotoxic to mammalian cells at therapeutic levels. Of additional interest, variation in the inhibitory effect was observed with different viruses, suggesting possible differences due to specific growth conditions of virus. SA-conjugated dendritic polymers may provide a new therapeutic modality for viruses that employ SA as their target receptor.

Solid-state microstructures, thermal properties, and crystallization of biodegradable poly(butylene succinate) (PBS) and its copolyesters

Studies of solid-state structures under different crystallization conditions, melting behavior, and crystal growth kinetics are reported for biodegradable aliphatic poly(butylene succinate) (PBS) and its random copolyesters of poly(butylene succinate-co-14 mol %ethylene succinate) [P(BS-co-14 mol %ES)] and poly(butylene succinate-co-15 mol %hexamethylene succinate) [P(BS-co-15 mol %HS)]. The crystal structures of two copolyesters determined by wide-angle X-ray diffraction (WAXD) are the same as that of the PBS homopolymer, suggesting that the second comonomers ES or HS units are excluded from the crystalline core and are in an amorphous state. The further investigations on the crystalline and amorphous phase structures and sizes by small-angle X-ray scattering (SAXS) method have provided quantitative evidence that the existence of second comonomers increases the amorphous thickness of copolyesters but that the influences of comonomers on the lamellar crystal structure and size of copolyesters are complicated. The origin of the complexity and its influences on the equilibrium melting temperature T(m)(0) of copolyester are discussed in the present paper. Gibbs-Thomson and Hoffman-Weeks equations were applied for the determination of T(m)(0) of PBS, P(BS-co-14 mol %ES), and P(BS-co-15 mol %HS)-three samples. Two equations gave different T(m)(0) values for each sample. On the basis of the Gibbs-Thomson equation, the P(BS-co-15 mol %HS) copolyester has the same T(m)(0) value as that of the PBS homopolymer, while the P(BS-co-14 mol %ES) copolyester has a lower one. This is due to the different influences of the second comonomers on the crystalline phase structure indicated by SAXS results, and the Gibbs-Thomson equation has been suggested to be more reliable. The crystal growth kinetics of the three samples was analyzed by using the secondary nucleation theory, and the influences of various parameters on the regime transition and nucleation constant were studied. Meanwhile some interrelations between regime transition temperature and melting behavior were found for the three samples.

High-field high-speed MAS resolution enhancement in 1H NMR spectroscopy of solids

Resolution in 1H NMR spectra of solids can be significantly enhanced with fast magic-angle spinning and high magnetic fields. A variable field and spinning speed study up to 25 T and 40 kHz shows that the homogeneous line broadening is inversely proportional to the product of magnetic field strength and spinning speed. The combination of high field and fast speed yields a 1H linewidth approaching the intrinsic limit determined by anisotropy of magnetic susceptibility. An analysis of the anisotropic magnetic susceptibility line broadening is presented.

Crystallization, melting, and enzymatic degradation of biodegradable poly(butylene succinate-co-14 mol % ethylene succinate) copolyester

The crystal structure and growth kinetics of melt-crystallized poly(butylene succinate-co-14 mol % ethylene succinate) [P(BS-co-14 mol % ES)] copolyester have been investigated at a wide crystallization temperature range of 30 to 90 degrees C. By means of wide-angle X-ray diffraction (WAXD), the copolyester composed of BS and ES units has been identified to have the same crystal structure with that of poly(butylene succinate) (PBS) homopolymer, suggesting that only PBS sequences crystallize while that the ES units are in an amorphous form. On the basis of secondary nucleation theory, two regimes of II and III have been observed and their transition temperature is around 80 degrees C. The spherulitic morphologies of P(BS-co-14 mol % ES) copolyester developed from banded spherulites to the normal ones without banding extinction patterns as the crystallization temperature increased. The melting behavior of P(BS-co-14 mol % ES) copolyester under different conditions has been studied by differential scanning calorimetry (DSC). Four melting peaks and one exothermal peak on the melting curves were observed during heating process, and their origination is discussed. The enzymatic degradation was carried out on the melt-crystallized P(BS-co-14 mol % ES) thin film by an extracellar PHB depolymerase from Pseudomonas stutzeri and the morphologies of lamellar crystals before and after degradation have been examined by atomic force microscopy (AFM). The results have indicated that enzymatically degradable ES units exist on the surface of lamellar crystals and are hydrolyzed by the enzyme, while that the crystalline cores composed of PBS chains are not degraded.

Biodegradable poly(ethylene succinate) (PES). 1. Crystal growth kinetics and morphology

Crystal growth rates of melt-crystallized poly(ethylene succinate) (PES) with a number-average molecular weight Mn of 21,100 and polydispersity of 1.86, respectively, were studied in an extensive temperature range. On the basis of secondary nucleation theory, only one transition between regime III and regime II was found at around 71 degrees C, but no transition of regime II-->I was detected by kinetic analysis. The ratio of nucleation constants KgIII in regime III to KgII in regime II was influenced by the value of activation energy U*, and tended to 2 as predicted by the theory when U* was set as 3688 cal/mol. The morphological changes at spherulitic level and lamellar level in regime II and regime III were examined by using an optical microscope (OM) and atomic force microscope (AFM). Although spherulitic morphologies were found in both regime II and regime III by optical microscopy, further investigations made by following the crystallization process using OM and by checking the lamellar morphology using AFM revealed morphological changes during the crystal growth process and different crystal morphologies in regime II and regime III. Meanwhile by using ultrathin film (approximately 100 nm in thickness), the morphology of lamellar crystals of lozenge-shape outline and composed of single crystals has been studied by AFM technique. The results indicate that there is indeed a transition from regime II to regime III at around 71 degrees C for the isothermal crystallization of PES with an increasing degree of undercooling.

Through-space R3-HETCOR experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR

We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n/2 (n>1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up.

Ultra-wide bore 900 MHz high-resolution NMR at the National High Magnetic Field Laboratory

Access to an ultra-wide bore (105 mm) 21.1 T magnet makes possible numerous advances in NMR spectroscopy and MR imaging, as well as novel applications. This magnet was developed, designed, manufactured and tested at the National High Magnetic Field Laboratory and on July 21, 2004 it was energized to 21.1 T. Commercial and unique homebuilt probes, along with a standard commercial NMR console have been installed and tested with many science applications to develop this spectrometer as a user facility. Solution NMR of membrane proteins with enhanced resolution, new pulse sequences for solid state NMR taking advantage of narrowed proton linewidths, and enhanced spatial resolution and contrast leading to improved animal imaging have been documented. In addition, it is demonstrated that spectroscopy of single site (17)O labeled macromolecules in a hydrated lipid bilayer environment can be recorded in a remarkably short period of time. (17)O spectra of aligned samples show the potential for using this data for orientational restraints and for characterizing unique details of cation binding properties to ion channels. The success of this NHMFL magnet illustrates the potential for using a similar magnet design as an outsert for high temperature superconducting insert coils to achieve an NMR magnet with a field >25 T.

Biodegradable poly(ethylene succinate) (PES). 2. Crystal morphology of melt-crystallized ultrathin film and its change after enzymatic degradation

Poly(ethylene succinate) (PES) ultrathin films with an initial thickness of approximately 100 nm were prepared by the solution cast method on either cover glass or freshly cleaved mica as the substrate. The ultrathin films were then melt-crystallized at a given temperature for a certain period of time. The surface morphologies of these films on the substrates were observed by an atomic force microscope (AFM) and an optical microscope (OM) under ambient conditions. Two different crystal morphologies having fibril-like structure and flat-on lamellar crystals with a certain width were formed, and their growth mechanisms were discussed in association with previous kinetic data. It has been shown that at a higher crystallization temperature such as 85 degrees C (smaller degree of undercooling) the crystal aggregates tend to form lozenge-shaped hedrites which evolved from a single crystal. The enzymatic degradation of PES crystals on the ultrathin films was carried out by using a PHB depolymerase from Pseudomonas stutzeri at room temperature. The crystal morphologies before and after enzymatic degradation were examined by AFM. The lamellar crystals were hydrolyzed into many small fragments, and these fragments had the same thickness as that of the lamellar crystals before enzymatic degradation. The analysis of morphological results for PES lamellar crystals has revealed the existence of many defects on the surface of melt-crystallized lamellar crystals. These defects were preferentially attacked by the enzyme molecules. Hydrolysis starts from the chains folding in crystal defect area and proceeds along the lateral edges, i.e., along the direction perpendicular to the folding chain.

Spin dynamics of polarization inversion spin exchange at the magic angle in multiple spin systems

Polarization inversion spin exchange at the magic angle (PISEMA) [J. Magn. Reson. A 109, 270 (1994)] is an important experiment in NMR structural characterization of membrane proteins in oriented lipid bilayers. This paper presents a theoretical and experimental study of the spin dynamics in PISEMA to investigate the line-narrowing mechanism. The study focuses on the effect of neighboring protons on the spin exchange of a strongly coupled spin pair. The spin exchange is solved analytically for simple spin systems and is numerically simulated for many-spin systems. The results show that the dipolar couplings from the neighboring protons of a strongly coupled spin pair perturb the spin exchange only in the second order, therefore it has little contribution to the linewidth of PISEMA spectra in comparison to the separated-local-field spectra. The effects from proton resonance offset and the mismatch of the Hartmann-Hahn condition are also discussed along with experimental results using model single-crystal samples.

Structural characterization of MAO and related aluminum complexes. 1. Solid-state (27)Al NMR with comparison to EFG tensors from ab initio molecular orbital calculations

Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.

Frequency- and phase-modulated heteronuclear decoupling in rotating solids

The mechanism of heteronuclear dipolar decoupling by the TPPM sequences, proposed by Bennett et al. (J. Chem. Phys. 103 (1995) 6951) is investigated by comparison with a modified pulse sequence, called TPFM, that uses frequency instead of phase modulation. By combining frequency and phase modulations, circularly modulated sequences are designed. The fact that only the left-handed modulation sequence FMPML leads to improved proton decoupling, while the right-handed modulation sequence FMPMR is ineffective, proves that the efficient decoupling is caused by a secondary resonance effect.

Traditional Uses, Chemical Constituents, Biological Properties, Clinical Settings, and Toxicities of Abelmoschus manihot L.: A Comprehensive Review

Abelmoschus manihot, an annual herbal flowering plant, is widely distributed throughout eastern Europe and in temperate and subtropical regions of Asia. Its flowers have been traditionally used for the treatment of chronic kidney disease in China. Currently, more than 128 phytochemical ingredients have been obtained and identified from the flowers, seeds, stems, and leaves of A. manihot. The primary components are flavonoids, amino acids, nucleosides, polysaccharides, organic acids, steroids, and volatile oils. A. manihot and its bioactive constituents possess a plethora of biological properties, including antidiabetic nephropathy, antioxidant, antiadipogenic, anti-inflammatory, analgesic, anticonvulsant, antidepressant, antiviral, antitumor, cardioprotective, antiplatelet, neuroprotective, immunomodulatory, and hepatoprotective activities, and have effects on cerebral infarction, bone loss, etc. However, insufficient utilization and excessive waste have already led to a rapid reduction of resources, meaning that a study on the sustainable use of A. manihot is urgent and necessary. Moreover, the major biologically active constituents and the mechanisms of action of the flowers have yet to be elucidated. The present paper provides an early and comprehensive review of the traditional uses, chemical constituents, pharmacological activities, and pharmaceutical, quality control, toxicological, and clinical settings to emphasize the benefits of this plant and lays a solid foundation for further development of A. manihot.

Relationships among deoxynivalenol, ergosterol and Fusarium exoantigens in Canadian hard and soft wheat

Soluble extracellular components (exoantigens) from cultures of Fusarium graminearum and F. sporotrichioides were used to produce antisera from chickens for an indirect enzyme immunoassay. This immunoassay was used to estimate Fusarium exoantigen levels in 40 samples of fusarium head blight-infected hard red spring wheat from Manitoba, and in 50 samples of infected soft white winter wheat from Ontario. These wheat samples were also assayed for deoxynivalenol (DON), the predominant Fusarium mycotoxin, and for ergosterol, a metabolite reflecting fungal biomass. Using F. sporotrichioides antisera, the linear correlations between exoantigen level and DON content for the hard and soft wheats had coefficients of 0.80 and 0.76, respectively. With the same antisera, linear correlations between exoantigen level and total ergosterol concentration for the hard and soft wheats had coefficients of 0.66 and 0.81, respectively.

New pillared layered gallium phosphonates in the gallium/1,2-ethylenediphosphonic acid system

1,2-Ethylenediphosphonic acid reacts with gallium nitrate in water to give new pillared layered gallium phosphonates, the structure of which depends on the experimental conditions used for their preparation. Thus, Ga(4)(O(3)PC(2)H(4)PO(3))(3) (1) and Ga(2)(OH)(2)(O(3)PC(2)H(4)PO(3)) (2) were isolated and the structure of 1 was solved by single-crystal X-ray diffraction, while 2 was shown to have the same metal/PO(3) arrangement as the previously described Ga(OH)(O(3)PCH(3)). Ga(4)(O(3)PC(2)H(4)PO(3))(3) (1) is triclinic, with space group P1 with Z = 2, a = 5.1480(4), b = 8.0354(7), and c = 12.383(1) A; alpha = 91.34(1), beta = 101.40(1), and gamma = 90.86(1) degrees; V = 501.9(1) A(3). The structure of 1 is unusual with (i) mixed GaO(4) and GaO(5) sites while a 6-fold coordination is observed for gallium in (2) and (ii) the presence of the organic moiety within both the layers and the interlayer space. The two compounds were fully characterized using (31)P and (71)Ga solid-state NMR.

Active-latent glycosylation strategy toward Lewis X pentasaccharide in a form suitable for neoglycoconjugate syntheses

Glycosylation of 4-nitrophenyl 2-acetamido-6-O-tert-butyldiphenylsilyl-2-deoxy-1-thio-beta-D-gluc opyranoside with phenyl 2,3,4,6-tetra-O-benzoyl-1-thio-beta-D-galactopyranoside in the presence of NIS and TfOH as catalyst gave the lactosamine derivative regiospecifically in high yield. Further 3-O-fucosylation with phenyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside using DMTST as promoter afforded the Lex trisaccharide intermediate. The latent glycosyl donor was transformed into its active form (p-acetamidothiophenyl) by reduction with zinc in acetic acid and N-acetylation. Glycosidation with p-nitrothiophenyl lactoside acceptor in the presence of NIS/TfOH as catalyst gave the Lex pentasaccharide in 71% yield.

Colorimetric competitive inhibition method for the quantification of avidin, streptavidin and biotin

A colorimetric competitive inhibition assay for avidin, streptavidin and biotin was developed. The method for avidin or streptavidin was based on the competitive binding between avidin or streptavidin and a streptavidin-enzyme conjugate for biotinylated dextrin immobilized on the surface of a microtitre plate. For biotin quantitation the competition is between free biotin and the immobilized biotin for the streptavidin-enzyme conjugate. The limits of detection which was determined as the concentration of competitor required to give 90% of maximal absorbency (100% inhibition) was approximately 20 ng/100 microl per assay for avidin and streptavidin and 0.4 pg/100 microl per assay for biotin. The methods are simple, rapid, highly sensitive and adaptable to high throughput analysis.