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| 2. |
- Griffiths, G, et al.
(författare)
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Characterization of the glycosyltransferase enzyme from the Escherichia coli K5 capsule gene cluster and identification and characterization of the glucuronyl active site.
- 1998
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 273:19, s. 11752-7
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial capsular polysaccharides play an important role in virulence and survival. The Escherichia coli K5 capsule consists of a repeat structure of -4)GlcA-beta(1,4)-GlcNAc alpha(1-, identical to N-acetylheparosan. A 60-kDa protein, KfiC, has been identified as a bifunctional glycosyltransferase, responsible for the alternating alpha and beta addition of each UDP-sugar to the nonreducing end of the polysaccharide chain. Using hydrophobic cluster analysis, a conserved secondary structure motif characteristic of beta-glycosyltransferases was identified along with two highly conserved aspartic acid residues at positions 301 and 352 within the KfiC protein. Site-directed mutagenesis was used to identify catalytically active amino acids within domain A of the KfiC protein. The conserved aspartic acid residues at 301 and 352 were shown to be critical for the beta addition of UDP-GlcA (uridine diphosphoglucuronic acid) to defined nonreducing end oligosaccharide acceptors, suggesting that these conserved aspartic acid residues are catalytically important for beta-glycosyltransferase activity. A deleted derivative of the kfiC gene was generated, which encoded for a truncated KfiC (kfiC') protein. This protein lacked 139 amino acids at the C terminus. This enzyme had no UDP-GlcA transferase activity but still retained UDP-GlcNAc transferase activity, indicating that two separate active sites are present within the KfiC protein.
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| 4. |
- Hodson, N, et al.
(författare)
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Identification that KfiA, a protein essential for the biosynthesis of the Escherichia coli K5 capsular polysaccharide, is an alpha -UDP-GlcNAcglycosyltransferase : The formation of a membrane-associated K5 biosynthetic complex requires KfiA, KfiB and KfiC.
- 2000
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 275:35, s. 27311-27315
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Tidskriftsartikel (refereegranskat)abstract
- The Escherichia coli K5 capsular polysaccharide consists of the repeat structure -4)GlcA-beta(1,4)-GlcNAc-alpha(1-and requires the KfiA, KfiB, KfiC, and KfiD proteins for its synthesis, Previously, the KfiC protein was shown to be a beta-UDP-GlcA glycosyltransferase, and KfiD was shown to be a UDP-Glc dehydrogenase. Here, we demonstrate that KfiA is an alpha-UDP-GlcNAc glycosyltransferase and that biosynthesis of the K5 polysaccharide involves the concerted action of the KfiA and KfiC proteins. By site-directed mutagenesis, we determined that the acidic motif of DDD, which is conserved between the C family of glycosyltransferases, is essential for the enzymatic activity of KfiA III addition, by Western blot analysis, we determined that association of KfiA with the cytoplasmic membrane requires KfiC but not KfiB, whereas the interaction of KfiC with the cytoplasmic membrane was dependent on both KfiA and KfiB. Likewise, KfiB was only detectable in cytoplasmic membrane fractions when both KfiA and KfiC were present. These data suggest that the interaction between the KfiA, KfiB, and KfiC proteins is essential for the stable association of these proteins with the cytoplasmic membrane and the biosynthesis of the K5 polysaccharide.
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| 5. |
- Lidholt, Kerstin, et al.
(författare)
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Biosynthesis of heparin : Modulation of polysaccharide chain length in a cell-free system
- 1988
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 254:2, s. 571-578
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Tidskriftsartikel (refereegranskat)abstract
- The formation of heparin-precursor polysaccharide (N-acetylheparosan) was studied with a mouse mastocytoma microsomal fraction. Incubation of this fraction with UDP-[3H]GlcA and UDP-GlcNAc yielded labelled macromolecules that could be depolymerized, apparently to single polysaccharide chains, by alkali treatment, and thus were assumed to be proteoglycans. Label from UDP-[3H]GlcA (approx. 3 microM) is transiently incorporated into microsomal polysaccharide even in the absence of added UDP-GlcNAc, probably owing to the presence of endogenous sugar nucleotide. When the concentration of exogenous UDP-GlcNAc was increased to 25 microM the rate of incorporation of 3H increased and proteoglycans carrying polysaccharide chains with an Mr of approx. 110,000 were produced. Increasing the UDP-GlcNAc concentration to 5 mM led to an approx. 4-fold decrease in the rate of 3H incorporation and a decrease in the Mr of the resulting polysaccharide chains to approx. 6000 (predominant component). When both UDP-GlcA and UDP-GlcNAc were present at high concentrations (5 mM) the rate of polymerization and the polysaccharide chain size were again increased. The results suggest that the inhibition of polymerization observed at grossly different concentrations of the two sugar nucleotides, UDP-GlcA and UDP-GlcNAc, may be due either to interference with the transport of one of these precursors across the Golgi membrane or to competitive inhibition of one of the glycosyltransferases. The maximal rate of chain elongation obtained, under the conditions employed, was about 40 disaccharide units/min. The final length of the polysaccharide chains was directly related to the rate of the polymerization reaction.
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