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11.
12.
Fucose is a major constituent of the protein- and lipid-linked glycans of
the various life-cycle stages of schistosomes. These fucosylated glycans
are highly antigenic and seem to play a role in the pathology of
schistosomiasis. In this article we describe the identification and
characterization of two fucosyltransferases (FucTs) in cercariae of the
avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1--
>4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R
alpha1-- >2-FucT. Triton X-100 extracts of cercariae were assayed for
FucT activity using a variety of acceptor substrates. Type 1 chain
(Galbeta1- ->3GlcNAc) based compounds were poor acceptors, whereas those
based on a type 2 chain (Galbeta1-->4GlcNAc), whether
alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether
present as oligosaccharide or contained in a glycopeptide or glycoprotein,
all served as acceptor substrates. In this respect the schistosomal alpha3-
FucT resembles human FucT V and VI rather than other known FucTs. N-
ethylmaleimide, an inhibitor of several human FucTs, had no effect on the
activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly
inhibitory. Large scale incubations were carried out with
Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and
Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the
products of the incubations were isolated using a sequence of
chromatographic techniques. By methylation analysis and 2D-TOCSY and
ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1--
>4[Fucalpha1-->2Fucalpha1-->3]GlcNAc,
GalNAcbeta1-->4[Fucalpha1-- >2Fucalpha1-->3]GlcNAcbe
ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1--
>3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-
FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric)
Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural
element that have been described on schistosomal glycoconjugates.
相似文献
13.
Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands 总被引:2,自引:2,他引:0
Britten CJ; van den Eijnden DH; McDowell W; Kelly VA; Witham SJ; Edbrooke MR; Bird MI; de Vries T; Smithers N 《Glycobiology》1998,8(4):321-327
The alpha3 fucosyltransferase, FucT-VII, is one of the key
glycosyltransferases involved in the biosynthesis of the sialyl Lewis X
(sLex) antigen on human leukocytes. The sialyl Lewis X antigen
(NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential
component of the recruitment of leukocytes to sites of inflammation,
mediating the primary interaction between circulating leukocytes and
activated endothelium. In order to characterize the enzymatic properties of
the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been
expressed in Trichoplusia ni insect cells. The enzyme is capable of
synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from
3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels
of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies
using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors
demonstrate that FucT-VII is able to synthesize both di-fucosylated and
tri-fucosylated structures from mono- fucosylated precursors, but
preferentially fucosylates the distal GlcNAc within a polylactosamine
chain. Furthermore, the rate of fucosylation of the internal GlcNAc
residues is reduced once fucose has been added to the distal GlcNAc. These
results indicate that FucT-VII is capable of generating complex selectin
ligands, in vitro , however the order of fucose addition to the lactosamine
chain affects the rate of selectin ligand synthesis.
相似文献
14.
We have identified a novel N -acetylgalactosaminyltransferase activity in
lactating bovine mammary gland membranes. Acceptor specificity studies and
analysis of products obtained in vitro by 400 MHz1H-NMR spectroscopy
revealed that the enzyme catalyses the transfer of N - acetylgalactosamine
(GalNAc) from UDP-GalNAc to acceptor substrates carrying a terminal,
beta-linked N -acetylglucosamine (GlcNAc) residue and establishes a
beta1-->4-linkage forming a GalNAcbeta1-->4GlcNAc ( N, N
'-diacetyllactosediamine, lacdiNAc) unit. Therefore, the enzyme can be
identified as a UDP-GalNAc:GlcNAcbeta-R beta1-->4-N-
acetylgalactosaminyltransferase (beta4-GalNAcT). This enzyme resembles
invertebrate beta4-GalNAcT as well as mammalian beta4-
galactosyltransferase (beta4-GalT) in acceptor specificity. It can,
however, be clearly distinguished from the pituitary hormone-specific
beta4-GalNAcT by its incapability of acting with an elevated activity on a
glycoprotein substrate carrying a hormone-specific peptide motif.
Furthermore, the GalNAcT activity appeared not to be due to a promiscuous
action of a beta4-GalT as could be demonstrated by comparing the
beta4-GalNAcT and beta4-GalT activities of the mammary gland, bovine
colostrum, and purified beta4-GalT, by competition studies with UDP-GalNAc
and UDP-Gal, and by use of an anti-beta4-GalT polyclonal inhibiting
antibody. Interestingly, under conditions where mammalian beta4-GalT forms
with alpha-lactalbumin (alpha-LA) the lactose synthase complex, the mammary
gland beta4-GalNAcT was similarly induced by alpha-LA to act on Glc with an
increased efficiency yielding the lactose analog GalNAcbeta1-->4Glc.
This enzyme thus forms the second example of a mammalian
glycosyltransferase the specificity of which can be modified by this milk
protein. It is proposed that the mammary gland beta4-GalNAcT functions in
the synthesis of lacdiNAc- based, complex-type glycans frequently occurring
on bovine milk glycoproteins. The action of this enzyme is to be considered
when aiming at the production of properly glycosylated protein
biopharmaceuticals in the milk of transgenic dairy animals.
相似文献
15.
16.
Michael Taschner Fruzsina Kotsis Philipp Braeuer E. Wolfgang Kuehn Esben Lorentzen 《The Journal of cell biology》2014,207(2):269-282
Cilia are microtubule-based organelles that assemble via intraflagellar transport (IFT) and function as signaling hubs on eukaryotic cells. IFT relies on molecular motors and IFT complexes that mediate the contacts with ciliary cargo. To elucidate the architecture of the IFT-B complex, we reconstituted and purified the nonameric IFT-B core from Chlamydomonas reinhardtii and determined the crystal structures of C. reinhardtii IFT70/52 and Tetrahymena IFT52/46 subcomplexes. The 2.5-Å resolution IFT70/52 structure shows that IFT52330–370 is buried deeply within the IFT70 tetratricopeptide repeat superhelix. Furthermore, the polycystic kidney disease protein IFT88 binds IFT52281–329 in a complex that interacts directly with IFT70/IFT52330–381 in trans. The structure of IFT52C/IFT46C was solved at 2.3 Å resolution, and we show that it is essential for IFT-B core integrity by mediating interaction between IFT88/70/52/46 and IFT81/74/27/25/22 subcomplexes. Consistent with this, overexpression of mammalian IFT52C in MDCK cells is dominant-negative and causes IFT protein mislocalization and disrupted ciliogenesis. These data further rationalize several ciliogenesis phenotypes of IFT mutant strains. 相似文献
17.
A covariotide model explains apparent phylogenetic structure of oxygenic photosynthetic lineages 总被引:17,自引:13,他引:4
Lockhart PJ; Steel MA; Barbrook AC; Huson DH; Charleston MA; Howe CJ 《Molecular biology and evolution》1998,15(9):1183-1188
The aims of the work were (1) to develop statistical tests to identify
whether substitution takes place under a covariotide model in sequences
used for phylogenetic inference and (2) to determine the influence of
covariotide substitution on phylogenetic trees inferred for photosynthetic
and other organisms. (Covariotide and covarion models are ones in which
sites that are variable in some parts of the underlying tree are invariable
in others and vice versa.) Two tests were developed. The first was a
contingency test, and the second was an inequality test comparing the
expected number of variable sites in two groups with the observed number.
Application of these tests to 16S rDNA and tufA sequences from a range of
nonphotosynthetic prokaryotes and oxygenic photosynthetic prokaryotes and
eukaryotes suggests the occurrence of a covariotide mechanism. The degree
of support for partitioning of taxa in reconstructed trees involving these
organisms was determined in the presence or absence of sites showing
particular substitution patterns. This analysis showed that the support for
splits between (1) photosynthetic eukaryotes and prokaryotes and (2)
photosynthetic and nonphotosynthetic organisms could be accounted for by
patterns arising from covariotide substitution. We show that the additional
problem of compositional bias in sequence data needs to be considered in
the context of patterns of covariotide/covarion substitution. We argue that
while covariotide or covarion substitution may give rise to
phylogenetically informative patterns in sequence data, this may not always
be so.
相似文献
18.
A Kourakis M Mouratidou G Kokkinos A Barbouti A Kotsis D Mourelatos J Dozi-Vassiliades 《Mutation research》1992,279(2):145-148
The frequency of chromosome aberrations was studied in peripheral blood lymphocytes of 29 workers occupationally exposed to a mixture of pesticides and in 14 age- and sex-matched healthy controls. There was a significant increase in chromosome aberrations in sprayers when compared to unexposed persons (2.39% compared to 0.54%). No positive correlation between the frequency of chromosome aberrations and the duration of exposure was observed. No significant difference between smokers and non-smokers was found. 相似文献
19.
20.
V G Tsakraklides E K Tsakraklides L K Kotsis S S Sotiropoulos G Patedakis T Grivas E Pektasides S Lykoudis 《BMJ (Clinical research ed.)》1980,281(6249):1194-1196
The interaction between speakers, audience, and chairmen was studied by 13 investigators during a medical meeting at which 356 free papers were given before a total audience of 2483 in 48 sessions. A protocol was used to score 21 questions relating to the presentation, 15 to the chairman of the session, and nine to the audience. Many speakers made technical faults in presentation and their use of slides. Most chairmen failed to comply with simple rules of procedure and with the expectations of speakers and audience. The interest of the audience was affected by the performance of speakers and chairman. Speakers should pay more attention to the technique of presentation, and organising committees of medical meetings should provide instructions to both speakers and chairmen. 相似文献