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.

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.

Isolation, affinity purification, and identification of piglet small intestine mucosa receptor for enterotoxigenic Escherichia coli k88ac+ fimbriae

An affinity chromatography technique was utilized to isolate and purify the receptors of Escherichia coli K88ac(+) fimbriae from the mucus of the small intestines of newborn piglets. Purified K88ac+ fimbriae were covalently immobilized onto a beaded agarose matrix (Sepharose 4B). The immobilized fimbriae were used for the affinity purification of the K88ac+ receptors. Only two major proteins were tightly and specifically bound to the immobilized fimbriae after the column containing bound receptor was washed exhaustively with a buffer containing a high concentration of salt and a detergent. The receptors were eluted as a single component at a low pH. The isolated proteins were then subjected to enzyme-linked immunosorbent assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western blot (immunoblot) analyses. The two proteins were of high purity, were responsible for nearly all of the fimbrial binding capacity of the crude mucus, and had molecular masses of 26 and 41 kDa. The method for isolation of E. coli binding proteins is simple and yields purified intestinal receptors in a single chromatographic run. The intestinal mucus of different piglets has different proportions of the two receptor proteins.

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.

[Detection of fungi from agricultural commodities with serological method]

The types of fungus antigen and the purification of fungus antigen, the purification of anti-fungus antibody, and the application of serology in detecting fungi from agricultural commodities are introduced. Fungi antigen are mainly from extra-cellular protein and extra-cellular polysaccharide. The method for antigen purification was the same as the common method used to separate and purify proteins and polysaccharides. The specificity of an antibody is the most important parameter for the quality of antibody. As long as the specificity of a antibody is high, the antibody could detect the target fungi from agricultural commodities.

Near-field mapping of the emission distribution in semiconductor microdiscs

We have used a scanning near-field optical microscope to study the fluorescent light distribution in the near- and far-fields with two types of microdiscs, InGaP and GaN, fabricated in our laboratory. The InGaP microdisc has a radius of 2.5-5.0 microm, a thickness of 0.15-0.2 microm and a circular shape and the GaN disc has a radius of 5-8 microm with a thickness of 0.5-2 microm. Spontaneous emission enhancement in these microdiscs has been observed with emitting wavelengths of 650 and 550 nm respectively In both types of microdisc, the whispering-gallery mode (WCM) has been observed on the top surface using near-field optical and far-field microscopic methods. However, due to the different disc structures and optical confinements, the light distributions of the type types of disc are quite different. In the case of the InGaP disc, WGM is the dominant mode with a mixture of other modes. Interference-like ring intensities have been observed both inside the disc surface and outside, with a period ratio of 1:2. In addition, the propagating waves emitted from the side of the disc have been collected for the first time by using near-field optical microscopy. A theoretical calculation based on the theory of optical modes in microdisc lasers confirmed this observation. It also predicted the behaviour of the electric field distribution (transverse electric) inside and outside the disc, as well as the period of the wave propagation. In contrast, the near-field mapping of the GaN fluorescence showed not only a ring-like emission intensity along the circumference of the disc, an indication of WGM, but also an even intensity distribution inside the disc. This can be explained as the combination of the WGM with the Fabry-Perot mode of multi-reflection between the GaN layer and the substrate. The results also demonstrate the potential application of near-field optics to explore the light emission mode of a microdisc on a nanometre scale.

Protease and protease inhibitor assays using biotinylated casein coated on a solid phase

A new type of solid-phase assay for proteases and protease inhibitors has been developed using biotinylated casein. The assay involves coating of titer plate wells with biotinylated casein, hydrolysis of this substrate with a protease such as trypsin, reaction of the biotin from the unhydrolyzed substrate with an alkaline phosphatase-streptavidin complex, and finally quantification of the amount of casein remaining on the plate using alkaline phosphatase activity as the indicator. The activity of the bound indicator enzyme is oppositely related to the protease activity of the sample. In addition, the assay can be modified for quantitating the corresponding amount of protease inhibitor in the sample. The assay is simple, sensitive, accurate, inexpensive, and amenable to automation.

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.

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.

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.

Biotinylated enzyme inhibitorsorbent assay: a specific method for quantitating enzyme and its inhibitor

A biotinylated enzyme inhibitorsorbent assay (BEISA) for quantitating enzyme and its inhibitor has been developed. The assay is based on the competition between unlabeled enzyme and biotin-labeled enzyme for binding by an immobilized inhibitor or between free inhibitor and the immobilized inhibitor for binding by a biotin-labeled enzyme followed by reaction of the biotin-bound complex with a streptavidin-alkaline phosphatase conjugate. The amount of enzyme or inhibitor can be determined from the intensity of color produced by the alkaline phosphatase acting on its substrate. Trypsin and its inhibitor from egg white (ovomucoid) were used as a model for the BEISA. The results indicated that the BEISA is a simple, sensitive, and specific method that can be used to quantitate the amount of an enzyme or its inhibitor and it is amenable to high-throughput analysis and automation. The BEISA can be also applied to any enzyme that has an appropriate inhibitor.

Radiofrequency-Driven and Slow-Magic-Angle-Sample-Spinning Polarization-Transfer Techniques: A Comparative Study

The rate constant of radiofrequency-driven (RF-driven) polarization transfer and that of polarization transfer under slow-magic-angle sample spinning (S-MAS) are compared using a model system, polycrystalline alpha-alpha'-13C2-phthalic acid. While the rate constant under RF irradiation in static samples strongly depends on the orientation of the internuclear vector, the rate constant under S-MAS is hardly sensitive to that orientation and, thus, depends almost exclusively on the internuclear distance. Consequently, polarization-transfer rate constants obtained under S-MAS can be interpreted more simply when used to study local order in polycrystalline or amorphous solids. Copyright 1998 Academic Press.

The characterization of chicken antibodies raised against Fusarium spp. by enzyme-linked immunosorbent assay and immunoblotting

Immunoassays for the detection of three Fusarium species have been developed. Chickens were immunized with the soluble antigens from within the mycelia (mycelia-soluble antigens) and the exoantigens of Fusarium sporotrichioides, Fusarium poae and Fusarium graminearum and the antigens were characterized using enzyme-linked immunosorbent assays, immunoblotting and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The cross-reactivities of antisera with eleven species of Fusarium, eleven species of fungi from other genera and the buffer-extracts of grain were determined. Antisera to the exoantigens and mycelia-soluble antigens did not cross-react with buffer-extracts of grain. The antisera against the mycelia-soluble antigens tended to cross-react with the antigens from other genera whereas the antisera against the exoantigens were genus specific. The antiserum raised against exoantigens from F. poae was species specific. The molecular weights of the immunodominant antigens from the Fusaria were above 28 kilodaltons. Antigens from Fusaria showed specific bands in SDS-PAGE gel that can be used to produce more specific antibodies. The results suggest that exoantigen immunoassay can be developed to identify Fusarium genus, whereas mycelia-soluble antigens are not suitable for immunoidentification among genus.

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.