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Synthesis of cyclic β-glucan using Laminarinase 16A glycosynthase mutant from the basidiomycete Phanerochaete chrysosporium
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
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2010 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 5, 1724-1730 p.Article in journal (Refereed) Published
Abstract [en]

Glycosynthases are precise molecular instruments for making specifically linked oligosaccharides. X-ray crystallography screening of ligands bound to the 1,3(4)-β-d-glucanase nucleophile mutant E115S of Phanerochaete chrysosporium Laminarinase 16A (Lam16A) showed that laminariheptaose (L7) bound in an arch with the reducing and nonreducing ends occupying either side of the catalytic cleft of the enzyme. The X-ray structure of Lam16A E115S in complex with α-laminariheptaosyl fluoride (αL7F) revealed how αL7F could make a nucleophilic attack upon itself. Indeed, when Lam16A E115S was allowed to react with αL7F the major product was a cyclic β-1,3-heptaglucan, as shown by mass spectrometry. NMR confirmed uniquely β-1,3-linkages and no reducing end. Molecular dynamics simulations indicate that the cyclic laminariheptaose molecule is not completely planar and that torsion angles at the glycosidic linkages fluctuate between two energy minima. This is the first report of a glycosynthase that joins the reducing and nonreducing ends of a single oligosaccharide and the first reported synthesis of cyclic β-glucan.

Place, publisher, year, edition, pages
American Chemical Society , 2010. Vol. 132, no 5, 1724-1730 p.
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-37223DOI: 10.1021/ja909129bISI: 000275084900063OAI: oai:DiVA.org:su-37223DiVA: diva2:295516
Available from: 2010-02-17 Created: 2010-02-17 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Exploring the structure of oligo- and polysaccharides: Synthesis and NMR spectroscopy studies
Open this publication in new window or tab >>Exploring the structure of oligo- and polysaccharides: Synthesis and NMR spectroscopy studies
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A deeper understanding of the diversity of carbohydrates and the many applications of oligo- and polysaccharides found in nature are of high interest. Many of the processes involving carbohydrates affect our everyday life. This thesis is based on six papers all contributing to an extended perspective of carbohydrate property and functionality. An introduction to carbohydrate chemistry together with a presentation of selected carbohydrate synthesis and analysis methods introduces the reader to the research field. The first paper is an NMR spectroscopy reinvestigation of the structures of the O-antigens from the lipopolysaccharides (LPS) of Shigella dysenteriae type 3 and Escherichia coli O124. The repeating units were concluded to be built of identical branched pentasaccharides now with the correct anomeric configurations. Paper II is a structural investigation of the O-antigen from the LPS of E. coli O74 which is built of branched tetrasaccharide repeating units including the uncommon monosaccharide d-Fuc3NAc. Paper III is a conformational study of a rhamnose derivative, using NMR spectroscopy and X-ray crystallography. The benzoyl ester group positioned at C4 prefers an “eclipsed” conformation in the crystal as well as in solution. The use of site-specifically 13C-labeled compounds in conformational studies is discussed in Papers IV and V. The disaccharide α-L-Rhap-(1→2)-α-L-Rhap-OMe was synthesized together with two 13C-isotopologues and studied with NMR spectroscopy to give seven J-couplings related to torsion angles φ and ψ. The trisaccharide α-L-Rhap-(1→2)[α-L-Rhap-(1→3)]-α-L-Rhap-OMe was synthesized with 13C-labeling at two positions which presented a solution to a problem of overlapping signals in the 1H NMR spectrum. The site-specific labeling also facilitated the measurement of two 3JCC and two 2JCH coupling constants. Finally, chapter 6 gives a short introduction to glycosynthase chemistry and discusses the synthesis of α-glycosyl fluorides. A novel cyclic heptasaccharide was synthesized from α-laminariheptaosyl fluoride using a mutant of the enzyme laminarase 16A and subsequently analyzed by NMR spectroscopy.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2010. 61 p.
Keyword
Carbohydrates, NMR spectroscopy, synthesis, lipopolysaccharides, conformational studies
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-37680 (URN)978-91-7447-041-3 (ISBN)
Public defence
2010-05-07, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.Available from: 2010-04-15 Created: 2010-03-19 Last updated: 2010-04-08Bibliographically approved

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