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Title: X-RAY STRUCTURE DETERMINATION AND MODELING OF THE CYCLIC TETRASACCHARIDE CYCLO{-6)-ALPHA-D-GLCP-(1-3)-ALPHA-D-GLCP-(1-6)-ALPHA-D-GLCP-(1-3)-ALPHA-D-GLCP-(1-}

Author
item BRADBROOK, GAIL - CNRS, BP
item GESSLER, KATRIN - CNRS, BP
item Cote, Gregory
item Momany, Frank
item BIELY, PETER - SLOVAK ACADEMY OF SCI
item PEREZ, SERGE - CNRS, BP
item IMBERTY, ANNE - CNRS, BP

Submitted to: Carbohydrate International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The cyclic tetrasaccharide cyclo{-6)-alpha-D-Glcp-(1-3)-alpha-D-Glcp- (1-6)-alpha-D-Glcp-(1-3)-alpha-D-Glcp-(1-} is the major compound obtained by activity of endo-alternases on the alternan polysaccharide. Crystals of this cyclo-tetra-glucose belong to the orthorhombic space group P212121 with a = 7.620(5), b = 12.450(5) and c = 34.800(5) Angstrom. The asymmetric unit contains one tetrasaccharide together with 5 water molecules. The tetrasaccharide adopts a plate-like overall shape with a very shallow depression on one side. The shape is not fully symmetrical and this appears very clearly when comparing the (Phi, Psi)torsion angles of the two alpha(1-6) linkages that have almost 10 deg differences in Phi and more than 20 deg differences in Psi. When analyzing the hydrogen bond network, it appears that its symmetry is indeed broken by an intramolecular hydrogen bond:O2 of glucose ring 1 being the donor to O2 of glucose ring 3. These two hydroxyl groups are located below the ring and their orientation, dictated by this hydrogen bond, makes the floor of the plate. Among the five water molecules, one has a very special position above the center of the plate and makes two three-centered hydrogen bonds that involves two ring and two glycosidic oxygens. This water molecule is seen to occupy perfectly the shallow depression in the plate shape of the tetrasaccharide. The influence of packing on the conformation has been analyzed by comparison with the conformation of the isolated molecule obtained by molecular modeling.