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81.
The catalytic domains of murine Golgi alpha1,2-mannosidases IA and IB that
are involved in N-glycan processing were expressed as secreted proteins in
P.pastoris . Recombinant mannosidases IA and IB both required divalent
cations for activity, were inhibited by deoxymannojirimycin and
kifunensine, and exhibited similar catalytic constants using
Manalpha1,2Manalpha-O-CH3as substrate. Mannosidase IA was purified as a 50
kDa catalytically active soluble fragment and shown to be an inverting
glycosidase. Recombinant mannosidases IA and IB were used to cleave
Man9GlcNAc and the isomers produced were identified by high performance
liquid chromatography and proton-nuclear magnetic resonance spectroscopy.
Man9GlcNAc was rapidly cleaved by both enzymes to Man6GlcNAc, followed by a
much slower conversion to Man5GlcNAc. The same isomers of Man7GlcNAc and
Man6GlcNAc were produced by both enzymes but different isomers of
Man8GlcNAc were formed. When Man8GlcNAc (Man8B isomer) was used as
substrate, rapid conversion to Man5GlcNAc was observed, and the same
oligosaccharide isomer intermediates were formed by both enzymes. These
results combined with proton-nuclear magnetic resonance spectroscopy data
demonstrate that it is the terminal alpha1, 2-mannose residue missing in
the Man8B isomer that is cleaved from Man9GlcNAc at a much slower rate.
When rat liver endoplasmic reticulum membrane extracts were incubated with
Man9GlcNAc2, Man8GlcNAc2was the major product and Man8B was the major
isomer. In contrast, rat liver Golgi membranes rapidly cleaved
Man9GlcNAc2to Man6GlcNAc2and more slowly to Man5GlcNAc2. In this case all
three isomers of Man8GlcNAc2were formed as intermediates, but a distinctive
isomer, Man8A, was predominant. Antiserum to recombinant mannosidase IA
immunoprecipitated an enzyme from Golgi extracts with the same specificity
as recombinant mannosidase IA. These immunodepleted membranes were enriched
in a Man9GlcNAc2to Man8GlcNAc2- cleaving activity forming predominantly the
Man8B isomer. These results suggest that mannosidases IA and IB in Golgi
membranes prefer the Man8B isomer generated by a complementary mannosidase
that removes a single mannose from Man9GlcNAc2.
相似文献
82.
Small-angle neutron and X-ray scattering have been used to investigate various aspects of the structural organization of adenovirus type 2. Neutron scattering allows the determination of the radial distribution of DNA and protein, which because of the highly icosahedral form of the virus allows it to be described in terms of three icosahedral shells. X-ray scattering shows that the distance between the major coat proteins (hexons) in the capsid is 100 +/- A. Evidence was also observed for an organization in the nucleoprotein core that gives rise to a maximum in the X-ray scattering at 1/29 A-1. 相似文献
83.
O Coux H G Nothwang K Scherrer W Bergsma-Schutter A C Arnberg P A Timmins J Langowski C Cohen-Addad 《FEBS letters》1992,300(1):49-55
Duck erythroblasts prosomes were analysed by small angle neutron scattering (SANS), dynamic light scattering and (cryo-)electron microscopy. A molecular weight of approximately 720,000 +/- 50,000, a radius of gyration of 64 +/- 2 A and a hydrodynamic radius of approximately 86 A were obtained. Electron micrographs show a hollow cylinder-like particle with a diameter of 120 A, a height of 170 A and a diameter of 40 A for the cavity, built of four discs, the two outer ones being more pronounced than those in the center. Results from SANS indicate less then 5% of RNA in the purified prosomes, but nuclease protection assays confirm its presence. 相似文献
84.
David J.S. Hulmes Andrew Miller Stephen W. White Peter A. Timmins Carment Berthet-Colominas 《International journal of biological macromolecules》1980,2(6):338-346
Measurement of fully corrected, low angle meridional neutron diffraction intensities from native collagen fibres, in a full range of H2O/D2O contrasts, is described. The observed contrast dependence of the intensities of the first 12 orders of 670 A (D) axial periodicity is fitted to a general quadratic theory of contrast variation. The observed first order contrast dependence is compared to predictions based on the amino acid sequence, assuming different extents of chemical H/D exchange, and found to be consistent with complete non-carbon linked H/D exchange except for 1 to 1.6 hydrogen atoms per gly-X-Ytriplet involved in H-bonding. Both X-ray and neutron diffraction data in a variety of contrasts are consistent with a unique model for the axially projected structure of native collagen fibrils based on the amino acid sequence. This model if characterized by average axial residua translations in the NH2 and COOH terminal, non-triple helical telopeptides, expressed as multiples of the triple helical residue translation, of 0.85 ± 0.05 and 0.7 ± 01 respectively, with D = 235 ± 1 residues. 相似文献
85.
Gu JQ Eppler CM Montenegro G Timmins SD Timmermann BN 《Zeitschrift für Naturforschung. C, Journal of biosciences》2005,60(7-8):527-533
Nematicidal bioassay-guided fractionation of the n-hexane extract of the seeds of Jubaea chilensis led to the identification of eight known fatty acids and a mixture of triglycerides, reported for the first time for this species. In addition, their corresponding methyl esters were identified to be artifacts generated during the extraction and isolation procedures by using GC-EI-MS and chemical transformation methods. The fatty acid composition of the triglycerides was analyzed by GC-EI-MS and chemical transformation techniques. Among the 17 compounds, only lauric acid and myristic acid exhibited significant inhibitory effects on the movement of Caenorhabditis elegans with minimum inhibitory concentrations (MIC) of 75 microg/ml. 相似文献
86.
Method for the generation and cultivation of functional three-dimensional mammary constructs without exogenous extracellular matrix 总被引:1,自引:0,他引:1
During puberty, pregnancy, lactation and post-lactation, breast tissue undergoes extensive remodelling and the disruption of these events can lead to cancer. In vitro studies of mammary tissue and its malignant transformation regularly employ mammary epithelial cells cultivated on matrigel or floating collagen rafts. In these cultures, mammary epithelial cells assemble into three-dimensional structures resembling in vivo acini. We present a novel technique for generating functional mammary constructs without the use of matrix substitutes. 相似文献
87.
Requirements for nitric oxide generation from isoniazid activation in vitro and inhibition of mycobacterial respiration in vivo
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Isoniazid (INH), a front-line antituberculosis agent, is activated by mycobacterial catalase-peroxidase KatG, converting INH into bactericidal reactive species. Here we investigated the requirements and the pathway of nitric oxide (NO*) generation during oxidative activation of INH by Mycobacterium tuberculosis KatG in vitro. We also provide in vivo evidence that INH-derived NO* can inhibit key mycobacterial respiratory enzymes, which may contribute to the overall antimycobacterial action of INH. 相似文献
88.
Liu W Rosenberg GA Shi H Furuichi T Timmins GS Cunningham LA Liu KJ 《Archives of biochemistry and biophysics》2004,426(1):11-17
Reactive oxygen species (ROS) have been implicated in the regulation of matrix metalloproteinases (MMPs). The xanthine/xanthine oxidase (X/XO) reaction has been widely used as a source of exogenous ROS in studying MMPs, but commercial XO has also been known to be contaminated by proteolytic activity, and MMPs are protease sensitive substrate. We have investigated the activation of proMMP-2 by X/XO in cultured vascular smooth muscle cells (SMCs). SMCs were incubated with X/XO (unpurified or purified) or XO alone for 24h. X/XO activated proMMP-2 in a dose-dependent manner. A similar profile was observed using XO. Purified XO produced lower amounts of active MMP-2 compared to unpurified XO. EPR study showed that X/XO, not XO itself, produced superoxide anion, which was completely scavenged by SOD. However, X/XO-induced proMMP-2 activation could not be inhibited by combination of SOD and catalase. Incubation with XO either in cell-free conditioned media or in cells resulted in similar amounts of active MMP-2, suggesting that membrane-type-MMPs were not involved in proMMP-2 activation. This was further confirmed by the lack of inhibitory effect of hydroxamate MMP inhibitor, BB1101. Aprotinin blocked unpurified XO-induced proMMP-2 activation in a dose-dependent manner, demonstrating the proteolytic activity contained in XO is essential. We conclude that proteolytic activity contained in XO, rather the ROS derived from X/XO, is responsible for proMMP-2 activation in cultured SMCs. The results also suggest that caution needs to be taken when interpreting the reported results on activation of MMPs where X/XO had been used as an "authentic" source of superoxide anion. 相似文献
89.
Matrix proteins are the driving force of assembly of enveloped viruses. Their main function is to interact with and polymerize at cellular membranes and link other viral components to the matrix-membrane complex resulting in individual particle shapes and ensuring the integrity of the viral particle. Although matrix proteins of different virus families show functional analogy, they share no sequence or structural homology, Their diversity is also evident in that they use a variety of late domain motifs to commit the cellular vacuolar protein sorting machinery to virus budding. Here, we discuss the structural and functional aspects of teh filovirus matrix protein VP40 and compare them to other known matrix protein structures from vesicular stomatitis virus adn retroviral matrix protein. 相似文献
90.
Lee JY Timmins JM Mulya A Smith TL Zhu Y Rubin EM Chisholm JW Colvin PL Parks JS 《Journal of lipid research》2005,46(10):2233-2245
Patients homozygous for Tangier disease have a near absence of plasma HDL as a result of mutations in ABCA1 and hypercatabolize normal HDL particles. To determine the relationship between ABCA1 expression and HDL catabolism, we investigated intravascular remodeling, plasma clearance, and organ-specific uptake of HDL in mice expressing the human apolipoprotein A-I (apoA-I) transgene in the Abca1 knockout background. Small HDL particles (7.5 nm), radiolabeled with (125)I-tyramine cellobiose, were injected into recipient mice to quantify plasma turnover and the organ uptake of tracer. Small HDL tracer was remodeled to 8.2 nm diameter particles within 5 min in human apolipoprotein A-I transgenic (hA-I(Tg)) mice (control) and knockout mice. Decay of tracer from plasma was 1.6-fold more rapid in knockout mice (P < 0.05) and kidney uptake was twice that of controls, with no difference in liver uptake. We also observed 2-fold greater hepatic expression of ABCA1 protein in hA-I(Tg) mice compared with nontransgenic mice, suggesting that overexpression of human apoA-I stabilized hepatic ABCA1 protein in vivo. We conclude that ABCA1 is not required for in vivo remodeling of small HDLs to larger HDL subfractions and that the hypercatabolism of normal HDL particles in knockout mice is attributable to a selective catabolism of HDL apoA-I by the kidney. 相似文献